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Published online before print December 21, 2005, 10.1148/radiol.2381042216

(Radiology 2005;238:454.)

A more recent version of this article appeared on December 1, 2005
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© RSNA, 2005

Cardiac Imaging

Mitral Regurgitation: Quantification with 16–Detector Row CT—Initial Experience1

Hatem Alkadhi, MD, Simon Wildermuth, MD, Dominique A. Bettex, MD, André Plass, MD, Bernhard Baumert, MD, Sebastian Leschka, MD, Lotus M. Desbiolles, MD, Borut Marincek, MD and Thomas Boehm, MD

1 From the Institute of Diagnostic Radiology (H.A., S.W., B.B., S.L., L.M.D., B.M., T.B.), Institute of Anesthesia, Division of Cardiovascular Anesthesia (D.A.B.), and Clinic for Cardiovascular Surgery (A.P.), University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland. Received December 31, 2004; revision requested March 3, 2005; revision received March 15; final version accepted April 15. Supported by the National Center of Competence in Research, Computer Aided and Image Guided Medical Interventions, of the Swiss National Science Foundation. Address correspondence to H.A. (e-mail: hatem.alkadhi{at}usz.ch).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Purpose: To prospectively determine if retrospectively electrocardiographic (ECG)-gated multi–detector row computed tomography (CT) with a 16–detector row CT scanner can depict mitral regurgitation and enable quantification of the severity of the disease.

Materials and Methods: The study had institutional review board approval, and patients gave informed consent. Nineteen patients with mitral regurgitation (10 men, nine women; mean age, 66 years ± 9 [standard deviation]; range, 41–83 years) and 25 patients without mitral regurgitation (14 men, 11 women; mean age, 68 years ± 9; range, 43–83 years) as determined with transesophageal color Doppler echocardiography and ventriculography underwent retrospectively ECG-gated 16–detector row CT. Twenty CT data sets covering the entire mitral valve apparatus were reconstructed in 5% steps of the R-R interval for each patient, and data analysis was performed with four-dimensional software. Using planimetry, two readers measured in consensus the area of the regurgitant orifice during systole. These measurements were compared with semiquantitative data from transesophageal echocardiography and ventriculography by using Spearman rank order correlation coefficients.

Results: In the 25 patients without mitral regurgitation, no regurgitant orifice during systole could be detected with multi–detector row CT. In the 19 patients with mitral regurgitation, a regurgitant orifice could be visualized in all cases. The mean regurgitant orifice area at CT—45 mm2 ± 34 (range, 10–148 mm2)—correlated significantly with the results at transesophageal echocardiography (r = 0.807, P < .001) and ventriculography (r = 0.922, P < .001).

Conclusion: Planimetric measurements of the regurgitant orifice area at retrospectively ECG-gated 16–detector row CT enable quantification of mitral regurgitation.

Supplemental material: radiology.rsnajnls.org/cgi/content/full/2381042216/DC1

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Mitral regurgitation is the most commonly encountered valve lesion in modern clinical practice (1). Regurgitant mitral valve lesions may progress insidiously, causing left ventricular (LV) damage before symptoms have developed. Therefore, mitral valve surgery has been advocated even for asymptomatic patients (2). Although physical examination can alert the clinician to the presence of clinically important regurgitation, diagnostic methods are usually needed to assess the severity of the disease (3).

Echocardiography is routinely used to examine patients suspected of having or known to have mitral regurgitation (4). Echocardiography is used to evaluate valve morphologic features in the assessment of the cause and mechanism of mitral regurgitation, to assess LV and left atrial (LA) function, and to grade the severity of mitral regurgitation. Although echocardiography is an excellent technique for detecting the presence of mitral regurgitation and defining the underlying pathologic cause, assessing and quantifying the severity of the leak can at times be difficult (5–7), and, to date, no reference standard for judging the relative accuracy of echocardiography is available (8). Nevertheless, echocardiography can enable a semiquantitative estimate of the severity of mitral regurgitation that is, in general, sufficient for clinical purposes (5).

Ventriculography is an invasive procedure that has long been used in routine practice to assess mitral regurgitation, and a clinical perception of the various grades of the disease at ventriculography is now widely shared and comprehended (9,10). Contrast material–enhanced ventriculography of the LV enables the assessment of end-diastolic and end-systolic volumes, stroke volume, and ejection fraction from biplane or single-plane silhouettes (11). Notwithstanding the pitfalls of ventriculography (12) and the fact that ventriculographic grading is not considered to be the reference standard (11), it can be used as a method for calibrating newly developed methods (7).

Multi–detector row computed tomography (CT) can enable the evaluation of both cardiac structure and function by permitting the assessment of coronary artery stenoses (13) and the quantification of ventricular ejection fractions (14). Moreover, results of a study of retrospectively electrocardiographic (ECG)-gated four–detector row CT (15) indicates that it depicts, with good quality, the morphologic and some structural pathologic features of the mitral valve. However, because only a single static CT image was acquired during mid-diastole in that study, it did not evaluate functional aspects of mitral valve disease such as regurgitation, stenosis, or valve prolapse. Thus, the purpose of our study was to prospectively determine if retrospectively ECG-gated multi–detector row CT with a 16–detector row CT unit can depict mitral regurgitation and enable quantification of the severity of the disease.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Patient Population
The study protocol was approved by the local ethics committee, and written informed consent was obtained from all patients. Informed consent included information about the potential risk of radiation from multi–detector row CT.

Within a 12-month period (between August 2003 and July 2004), we prospectively enrolled 92 patients with known coronary artery disease who were referred for a multi–detector row CT examination of their coronary arteries as part of another study. Exclusion criteria included renal insufficiency (creatinine level, >120 µmol/L), a history of adverse reaction to iodinated contrast medium, and arrhythmia. Eleven patients were excluded because of an elevated serum creatinine level (n = 7), a previous allergic reaction to iodine-based contrast medium (n = 3), or arrhythmia (n = 1). Among the remaining 81 patients, all 19 who had mitral regurgitation (10 men, nine women; mean age, 66 years ± 9 [standard deviation]; age range, 41–83 years) were included in our study. For comparison, 25 randomly selected patients without mitral regurgitation (14 men, 11 women; mean age, 68 years ± 9; age range, 43–83 years) from among the same group of 81 patients were included as a control group. No significant difference with regard to age or sex (P = .72 and P = .70, respectively; Mann-Whitney U test) was present between the group of patients with mitral regurgitation and the group without mitral regurgitation. Similarly, LV ejection fractions were not significantly different between the group of patients with mitral regurgitation (median LV ejection fraction, 68; range, 46–84) and the group without mitral regurgitation (median, 60; range, 35–82) (P = .42, Mann-Whitney U test).

Presence or absence of mitral regurgitation had been determined with transesophageal echocardiography (TEE) and ventriculography in all 44 patients. All 44 patients had coronary artery disease, 16 patients also had aortic regurgitation (nine of these patients had mitral regurgitation and seven did not), 19 patients also had aortic stenosis (13 of these patients had mitral regurgitation and six did not), and one patient without mitral regurgitation had a patent foramen ovale. Sixteen patients had a recent history of myocardial infarction (eight of these patients had mitral regurgitation and eight did not). Multi–detector row CT, TEE, and ventriculography were performed within 3 days of each other. All patients underwent cardiac bypass graft surgery, and nine patients also underwent mitral valve surgery.

Ventriculography and Interpretation
Ventriculography was performed with a cardiac angiography unit (Bicor C; Siemens Medical Solutions, Forchheim, Germany) in biplane 30° right anterior oblique and 60° left anterior oblique standard projections and a 15° craniocaudal angulation as part of diagnostic coronary angiography. A 6-F pigtail catheter was used, and 35–45 mL of iopromide (Ultravist 300, 300 mg of iodine per milliliter; Schering, Berlin, Germany) was administered at a flow rate of 12 mL/sec. The severity of mitral regurgitation was rated according to the classic grading scheme (9–11): In mild (grade 1) mitral regurgitation, the regurgitant volume essentially clears with each heartbeat and never opacifies the entire LA; in moderate (grade 2) mitral regurgitation, the regurgitant volume does not clear with one heartbeat and does not opacify the entire LA after several heartbeats—however, opacification of the LA does not equal that of the LV; in moderately severe (grade 3) mitral regurgitation, the LA is completely opacified and achieves opacification that is equal to that of the LV; and in severe (grade 4) mitral regurgitation, LA opacification occurs within one heartbeat and becomes progressively more dense with each heartbeat and contrast material can be seen refluxing into the pulmonary veins during LV systole. Ventriculographic results were interpreted at the time of catheterization by the same angiographer who performed the examination. This angiographer had 7 years of experience in ventriculography and was blinded to the results of the other imaging modalities.

TEE and Interpretation
Intraoperative TEE was performed by using a standardized database and reporting system (16); results were recorded on videotape. A multiplanar 5-MHz TEE probe (Sonos 5500; Philips, Andover, Mass) equipped with pulsed wave, continuous wave, and color Doppler capabilities was used. All TEE examinations included B- and M-mode echocardiography combined with color Doppler examination and were performed according to the guidelines of the American Society of Echocardiography (17). The mitral valve was examined with bidimensional echocardiography, as well as with color and spectral Doppler, in four midesophageal (0°, 60°, 90°, and 120°) and two transgastric (0° and 90°) views.

The severity of mitral regurgitation was graded according to the following combined criteria (5,8,11,18–20): Mitral regurgitation was considered mild (grade 1) when there was a central color flow jet that extended less than halfway back into the body of the LA and an incomplete spectral envelope and the vena contracta (ie, the narrowest central flow region of the regurgitant jet) measured less than 3.0 cm in width; moderate (grade 2) when the color flow jet extended more than halfway back into the LA, there was a complete spectral envelope, the severity of the regurgitant jet was less than the inflow, and the width of the vena contracta ranged from 0.3 to 0.5 cm; and severe (grade 3) when the color flow jet filled more than two-thirds of the LA and extended to the posterior LA wall, there was a complete spectral envelope, the density equaled the inflow, and the width of the vena contracta was greater than 0.5 cm. The same experienced echocardiographer (D.A.B.), who was blinded to the results of the other imaging modalities, performed all TEE examinations and interpreted the results. The echocardiographer assessed the results of the TEE examinations by using the same classification system used at CT (see below).

Multi–Detector Row CT
All 44 patients had a sinus rhythm (mean heart rate, 69 beats per minute ± 8; range, 44–84 beats per minute), and no ß-receptor–blocking medication was administered before the CT examination. Multi–detector row CT was performed with a 16–detector row CT scanner (Sensation 16; Siemens Medical Solutions) with a gantry rotation time of 0.375 second. One hundred milliliters of iodixanol (Visipaque 320, 320 mg of iodine per milliliter; Amersham Health, Buckinghamshire, England) was administered through a 20–22-gauge needle, which was placed into a superficial vein in the antecubital fossa. The contrast medium was administered by using a power injector (CT Injector; Ulrich Medical, Ulm-Jungingen, Germany) at a rate of 4 mL/sec.

For optimal intraluminal contrast enhancement, the delay time between the start of contrast medium administration and the start of imaging was determined for each patient by using a bolus-tracking technique (CARE-Bolus; Siemens). The region of measurement was placed in the ascending aorta, and the threshold was set at 150 HU. The contrast medium bolus was followed by a 30-mL saline chaser bolus administered at the same flow rate. Repetitive low-dose monitoring examinations (120 kV, 10 mA, 0.5-second scanning time, 1-second interscan delay) were performed 10 seconds after contrast medium injection began. After the preset contrast enhancement level of 150 HU was reached, the multi–detector row CT examination was automatically initiated. Data acquisition was performed in a craniocaudal direction with a section thickness of 0.75 mm, a table feed of 3 mm per rotation, and a gantry rotation of 0.375 second (pitch, 0.25). The x-ray tube potential was 120 kV, and the effective tube current was 550 mA.

Postprocessing of CT Data
For image reconstruction, a segmented adaptive cardiac reconstruction algorithm was used (21). This algorithm uses raw data from one subsegment of consecutive multisection spiral CT data from the same heart cycle at heart rates of less than 65 beats per minute. At higher heart rates, two subsegments from adjacent heart cycles contribute to the partial scan data segment. Transverse CT images were reconstructed by using a section thickness of 1 mm and an increment of 0.5 mm. The reconstructed field of view was individually fitted to the actual cardiac size in each patient (mean field of view, 209 mm ± 17; range, 175–255 mm; image matrix, 512 x 512 pixels). Twenty data sets of transverse images at 5% steps of the R-R interval were reconstructed for each patient by using a Bf30 medium soft-tissue kernel. These data sets were then loaded into an interactive image-processing software (Syngo InSpace4D; Siemens) that is capable of three-dimensional processing in real time and can thus display the beating heart in any desired plane. The velocity of video presentation could be individually determined, and the readers (see below) were allowed to pause the cine-mode videos and scroll through the volume and phases until they found the best image for visualizing a particular structure or pathologic feature. The readers were also allowed to individually adjust window width and level settings for image analysis.

CT Image Analysis
The multi–detector row CT data sets were presented in a random order to two blinded readers (T.B. and S.W., each with 5 years of experience with cardiac CT) who analyzed all data in consensus. They were blinded to the clinical data and to the results of TEE and ventriculography—that is, they were not aware of whether the patient had mitral regurgitation, nor did they know the degree of possible mitral regurgitation. First, the readers visually inspected (on long-axis planes in the orientation of the LV) the entire mitral valve apparatus on the cine-mode videos with regard to the presence or absence of mitral regurgitation—that is, incompetent mitral valve closure during systole. If mitral regurgitation was present, the readers froze the cine-mode video during the phase in systole at which the incomplete regurgitant orifice area (ROA) was maximal. Then, the readers reconstructed an image perpendicular to this plane and parallel to the regurgitant orifice on which the regurgitant orifice had the smallest diameter. Finally, by using an electronic caliper, the inner contour of the regurgitant orifice was manually outlined, thus enabling calculation of the ROA in square millimeters.

The same two blinded readers systematically assessed the morphologic features of the valve apparatus at multi–detector row CT in consensus. The following morphologic abnormalities were assessed: calcification of the mitral annulus, thickening and calcification of the leaflets, valve prolapse (defined as billowing of one or both leaflets ≥ 2 mm beyond the mitral annulus plane during systole [11]), and rupture or thickening of tendinous cords and papillary muscles. If thickening of valve leaflets or mitral annulus calcification was present, the degree was classified according to the following criteria (15,22): A grade of I indicated that the free edges of the valve leaflets and the mitral annulus were thicker than 2 but thinner than or equal to 5 mm; and a grade of II, that the free edges of the valve leaflets and the mitral annulus were thicker than 5 mm. All measurements at multi–detector row CT and TEE were performed with electronic calipers.

Mitral Valve Surgery and Histopathologic Examination
Nine patients underwent mitral valve surgery, and histopathologic analysis of surgical specimens was performed. The indication for valve surgery was based on clinical, TEE, and ventriculographic findings, and the decision to perform valve repair and reconstruction or valve replacement was based on the extent of valve calcifications. Intraoperatively, the surgeon evaluated mitral valve abnormalities (ie, thickening and calcification of valve leaflets or annulus calcification) by direct visualization and digital inspection. Because visualization and digital inspection do not allow quantitative assessment of valve pathologic features, the data from surgery could not be used for statistical comparison with multi–detector row CT and TEE data.

Statistical Analysis
Statistical analysis was performed by using commercially available software (SSPS, version 11.5 for Windows; SPSS, Chicago, Ill). Quantitative variables are expressed as mean values ± standard deviations. The relationship between the semiquantitative severity of mitral regurgitation at ventriculography and TEE and the quantitative ROA measurements at multi–detector row CT was examined by using Spearman rank order correlation coefficients. Analysis of variance with the Fisher least significant difference procedure was performed to compare ROA values at multi–detector row CT after they were graded according to echocardiographic and ventriculographic definitions. Intermodality agreement between multi–detector row CT and echocardiography regarding morphologic valve abnormalities were expressed as Cohen {kappa} statistics (23). The Cohen {kappa} results were interpreted according to the method of Landis and Koch (24) as follows: A {kappa} value of 0.20 or less indicated poor agreement; a {kappa} value of 0.21–0.40, fair agreement; a {kappa} value of 0.41–0.60, moderate agreement; a {kappa} value of 0.61–0.80, good agreement; and a {kappa} value of 0.81–1.00, excellent agreement. P < .05 was considered to indicate a statistically significant difference.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Multi–detector row CT, TEE, and ventriculography were performed successfully in all 44 patients with no complications. Mitral regurgitation was considered to be organic (defined as intrinsic valve disease [11]) in all 19 patients. No patient had functional mitral regurgitation (a structurally normal valve with leakage caused by an extravalvular abnormality). The cause of mitral regurgitation was degenerative disease in 18 patients and endocarditis in one patient.

Grading of Mitral Regurgitation and Assessment of Morphologic Valve Abnormalities
On the basis of the ventriculography results, five patients had mild (grade 1) mitral regurgitation, four had moderate (grade 2) mitral regurgitation, five had moderately severe (grade 3) mitral regurgitation, and five had severe (grade 4) mitral regurgitation (median mitral regurgitation grade, 3; range, 1–4).

On the basis of the TEE results, six patients had mild (grade 1) mitral regurgitation, five had moderate (grade 2) mitral regurgitation, and eight had severe (grade 3) mitral regurgitation (median mitral regurgitation grade, 2; range, 1–3).

Multi–detector row CT revealed normal and complete coaptation of the valve leaflets during systole in all 25 patients who did not have mitral regurgitation (as known from TEE and ventriculographic results)—that is, no false-positive judgment regarding mitral regurgitation was made. In all 19 patients with mitral regurgitation, incompetent valve closure during systole was detected with multi–detector row CT. The planimetric measurements of the ROA ranged from 10 to 148 mm2, with a mean of 45 mm2 ± 34. Nonparametric Spearman rank order correlation between ROA measurements at multi–detector row CT and semiquantitative assessments of mitral regurgitation with TEE (Fig 1) was significant: r = 0.807 and P < .001. A significant correlation was also found between the ROA measurements at multi–detector row CT and the semiquantitative assessments of mitral regurgitation with ventriculography: r = 0.922 and P < .001.



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  		Figure 1a: (a) Scatterplot of data regarding severity of mitral regurgitation at TEE and planimetric ROA measurements at multi–detector row CT (MDCT) shows the high degree of correlation between the two variables. (b) Scatterplot of data regarding severity of mitral regurgitation at ventriculography and planimetric ROA measurements at multi–detector row CT shows the high degree of correlation between the two variables. n = Number of patients with mitral regurgitation.

 


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  		Figure 1b: (a) Scatterplot of data regarding severity of mitral regurgitation at TEE and planimetric ROA measurements at multi–detector row CT (MDCT) shows the high degree of correlation between the two variables. (b) Scatterplot of data regarding severity of mitral regurgitation at ventriculography and planimetric ROA measurements at multi–detector row CT shows the high degree of correlation between the two variables. n = Number of patients with mitral regurgitation.

 
When the ventriculography results were applied to the ROA measurements, the five patients with mild (grade 1) mitral regurgitation were found to have a mean ROA of 15 mm2 ± 5, the four patients with moderate (grade 2) mitral regurgitation were found to have a mean ROA of 29 mm2 ± 7, the five patients with moderately severe (grade 3) mitral regurgitation were found to have a mean ROA of 47 mm2 ± 9, and the five patients with severe (grade 4) mitral regurgitation were found to have a mean ROA of 88 mm2 ± 44. With this grading system, ROA values for mild mitral regurgitation were significantly different from those for moderately severe and severe mitral regurgitation (P < .049 and P < .001, respectively), and ROA values for moderate mitral regurgitation were significantly different from those for severe mitral regurgitation (P < .002). Nonsignificant differences were present between mild and moderate mitral regurgitation (P = .383) and between moderate and moderately severe mitral regurgitation (P = .280). Figures 2–4 show examples of the multi–detector row CT appearance and the corresponding TEE and ventriculographic appearance in patients with mild, moderate, and severe mitral regurgitation. Movie 1 (radiology.rsnajnls.org/cgi/content/full/2381042216/DC1) shows cine-loop CT images of a regurgitant mitral valve.



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  		Figure 2a: (a) Oblique CT image through long axis of LV and LA during systole (at 5% of the R-R interval) in 53-year-old man shows incomplete coaptation of the anterior and posterior mitral valve leaflets that creates a regurgitant orifice (arrowheads). Inset: Reconstruction perpendicular to the regurgitant orifice shows the ROA (arrowheads); planimetric measurements indicated that the ROA was 15 mm2. (b) Corresponding TEE image in two-chamber view at 90° similarly shows the incompetent valve closure (arrowheads) during systole. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered mild (grade 1) in this patient. (c) Ventriculogram in 60° left anterior oblique projection shows flow of contrast medium (arrowheads) into the LA during systole; this mitral regurgitation was considered mild (grade 1).

 


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  		Figure 2b: (a) Oblique CT image through long axis of LV and LA during systole (at 5% of the R-R interval) in 53-year-old man shows incomplete coaptation of the anterior and posterior mitral valve leaflets that creates a regurgitant orifice (arrowheads). Inset: Reconstruction perpendicular to the regurgitant orifice shows the ROA (arrowheads); planimetric measurements indicated that the ROA was 15 mm2. (b) Corresponding TEE image in two-chamber view at 90° similarly shows the incompetent valve closure (arrowheads) during systole. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered mild (grade 1) in this patient. (c) Ventriculogram in 60° left anterior oblique projection shows flow of contrast medium (arrowheads) into the LA during systole; this mitral regurgitation was considered mild (grade 1).

 


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  		Figure 2c: (a) Oblique CT image through long axis of LV and LA during systole (at 5% of the R-R interval) in 53-year-old man shows incomplete coaptation of the anterior and posterior mitral valve leaflets that creates a regurgitant orifice (arrowheads). Inset: Reconstruction perpendicular to the regurgitant orifice shows the ROA (arrowheads); planimetric measurements indicated that the ROA was 15 mm2. (b) Corresponding TEE image in two-chamber view at 90° similarly shows the incompetent valve closure (arrowheads) during systole. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered mild (grade 1) in this patient. (c) Ventriculogram in 60° left anterior oblique projection shows flow of contrast medium (arrowheads) into the LA during systole; this mitral regurgitation was considered mild (grade 1).

 


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  		Figure 3a: (a) Oblique CT image through long axis of LV and LA in 66-year-old man shows incompetent mitral valve closure during systole (at 10% of the R-R interval); the leaflets create a regurgitant orifice (arrowheads). Note the thickened tendinous cords (arrows) and the thickened free margin of the anterior leaflet. Inset: Perpendicular reconstruction clearly shows the regurgitant orifice (arrowheads); planimetric measurements indicated that the ROA was 46 mm2. (b) TEE image in four-chamber view at 0° similarly shows the incomplete coaptation (arrowheads), thickened tendinous cords (arrows), and thickened leaflets. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered moderate (grade 2) in this patient. (c) Ventriculogram obtained in 60° left anterior oblique projection shows contrast medium backflow (arrowheads) from the LV into the LA during systole; this mitral regurgitation was considered moderately severe (grade 3).

 


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  		Figure 3b: (a) Oblique CT image through long axis of LV and LA in 66-year-old man shows incompetent mitral valve closure during systole (at 10% of the R-R interval); the leaflets create a regurgitant orifice (arrowheads). Note the thickened tendinous cords (arrows) and the thickened free margin of the anterior leaflet. Inset: Perpendicular reconstruction clearly shows the regurgitant orifice (arrowheads); planimetric measurements indicated that the ROA was 46 mm2. (b) TEE image in four-chamber view at 0° similarly shows the incomplete coaptation (arrowheads), thickened tendinous cords (arrows), and thickened leaflets. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered moderate (grade 2) in this patient. (c) Ventriculogram obtained in 60° left anterior oblique projection shows contrast medium backflow (arrowheads) from the LV into the LA during systole; this mitral regurgitation was considered moderately severe (grade 3).

 


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  		Figure 3c: (a) Oblique CT image through long axis of LV and LA in 66-year-old man shows incompetent mitral valve closure during systole (at 10% of the R-R interval); the leaflets create a regurgitant orifice (arrowheads). Note the thickened tendinous cords (arrows) and the thickened free margin of the anterior leaflet. Inset: Perpendicular reconstruction clearly shows the regurgitant orifice (arrowheads); planimetric measurements indicated that the ROA was 46 mm2. (b) TEE image in four-chamber view at 0° similarly shows the incomplete coaptation (arrowheads), thickened tendinous cords (arrows), and thickened leaflets. Inset: Color Doppler echocardiogram shows a jet (arrowheads) regurgitating into the LA; mitral regurgitation was considered moderate (grade 2) in this patient. (c) Ventriculogram obtained in 60° left anterior oblique projection shows contrast medium backflow (arrowheads) from the LV into the LA during systole; this mitral regurgitation was considered moderately severe (grade 3).

 


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  		Figure 4a: (a) Oblique CT image through long axis of LV and LA during systole (at 10% of the R-R interval) in 58-year-old woman shows incompetent coaptation (arrowheads) and billowing of both leaflets (arrows); this appearance defines valve prolapse. Inset: Perpendicular reconstruction shows the 65-mm2 regurgitant orifice (arrowheads). (b) TEE image in commissural view at 60° similarly shows the incomplete valve closure (arrowheads) and prolapse of both leaflets (arrows). Inset: Color Doppler echocardiogram shows a substantial regurgitant jet (arrowheads) that creates turbulent flow in the LA; mitral regurgitation was consequently considered severe (grade 3). (c) Ventriculogram in 60° left anterior oblique projection shows contrast material backflow during systole into the LA (white arrowheads) and pulmonary veins (black arrowheads)—findings consistent with severe (grade 4) regurgitation.

 


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  		Figure 4b: (a) Oblique CT image through long axis of LV and LA during systole (at 10% of the R-R interval) in 58-year-old woman shows incompetent coaptation (arrowheads) and billowing of both leaflets (arrows); this appearance defines valve prolapse. Inset: Perpendicular reconstruction shows the 65-mm2 regurgitant orifice (arrowheads). (b) TEE image in commissural view at 60° similarly shows the incomplete valve closure (arrowheads) and prolapse of both leaflets (arrows). Inset: Color Doppler echocardiogram shows a substantial regurgitant jet (arrowheads) that creates turbulent flow in the LA; mitral regurgitation was consequently considered severe (grade 3). (c) Ventriculogram in 60° left anterior oblique projection shows contrast material backflow during systole into the LA (white arrowheads) and pulmonary veins (black arrowheads)—findings consistent with severe (grade 4) regurgitation.

 


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  		Figure 4c: (a) Oblique CT image through long axis of LV and LA during systole (at 10% of the R-R interval) in 58-year-old woman shows incompetent coaptation (arrowheads) and billowing of both leaflets (arrows); this appearance defines valve prolapse. Inset: Perpendicular reconstruction shows the 65-mm2 regurgitant orifice (arrowheads). (b) TEE image in commissural view at 60° similarly shows the incomplete valve closure (arrowheads) and prolapse of both leaflets (arrows). Inset: Color Doppler echocardiogram shows a substantial regurgitant jet (arrowheads) that creates turbulent flow in the LA; mitral regurgitation was consequently considered severe (grade 3). (c) Ventriculogram in 60° left anterior oblique projection shows contrast material backflow during systole into the LA (white arrowheads) and pulmonary veins (black arrowheads)—findings consistent with severe (grade 4) regurgitation.

 
When the TEE results were applied to the ROA measurements, the six patients with mild (grade 1) mitral regurgitation were found to have a mean ROA of 21 mm2 ± 9, the five patients with moderate (grade 2) mitral regurgitation were found to have a mean ROA of 32 mm2 ± 16, and the eight patients with severe (grade 3) mitral regurgitation were found to have a mean ROA of 72 mm2 ± 37. With this grading system, ROA values for mild mitral regurgitation were not significantly different from those for moderate mitral regurgitation (P = .493). ROA values were significantly different between mild and severe mitral regurgitation (P < .002) and between moderate and severe mitral regurgitation (P < .017).

Mitral annulus calcification and leaflet thickening, respectively, were detected with both TEE and multi–detector row CT in seven and 11 of the 25 patients without mitral regurgitation. In this patient group, intermodality agreement between TEE and multi–detector row CT regarding the grading of the thickness of mitral annulus calcification and valve leaflets was excellent ({kappa} = 1.00). Rupture or thickening of tendinous cords and valve prolapse were not depicted in this patient group with either modality.

In the 19 patients with mitral regurgitation, the findings at multi–detector row CT regarding mitral annulus calcification and thickening of the leaflets and tendinous cords correlated exactly with the findings at TEE (Table). Similarly, intermodality agreement regarding the grading of the thickness of mitral annulus calcification and valve leaflets was excellent ({kappa} = 1.00). Similarly, valve prolapse was diagnosed in 10 patients with both TEE and multi–detector row CT ({kappa} = 1.00). In two patients, both the anterior and the posterior leaflets were affected, whereas only the posterior leaflet was affected in six patients and only the anterior leaflet was affected in two patients. Rupture of tendinous cords was depicted preoperatively with TEE in three patients and was not seen at multi–detector row CT in any patient (poor intermodality agreement). Thickening of tendinous cords was revealed in the same two patients with both TEE and multi–detector row CT ({kappa} = 1.00). Figure 5 shows example multi–detector row CT and TEE images of typical morphologic abnormalities of the valve apparatus associated with mitral regurgitation.


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  		Number of Morphologic Abnormalities of Mitral Valve Apparatus in 19 Patients with Mitral Regurgitation Diagnosed with TEE and CT

 


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  		Figure 5a: (a) Oblique CT image through long axis of LV and LA (at 5% of the R-R interval) shows grade I (>2 but ≤5 mm) calcification of the anterior leaflet (white arrowhead) and grade II (>5 mm) calcification of the posterior mitral annulus (black arrowhead). (b) Corresponding TEE image (two-chamber view at 0°) similarly shows both foci of calcification (white and black arrowheads), which cause acoustic shadowing. (c) Oblique CT reconstruction through long axis of LV and LA shows posterior leaflet prolapse (arrowhead). (d) TEE image (two-chamber view at 0°) similarly shows a flail posterior leaflet (arrowhead) with cordal rupture. A rupture of tendinous cords (as verified during surgery) was suspected but could not be directly demonstrated with CT.

 


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  		Figure 5b: (a) Oblique CT image through long axis of LV and LA (at 5% of the R-R interval) shows grade I (>2 but ≤5 mm) calcification of the anterior leaflet (white arrowhead) and grade II (>5 mm) calcification of the posterior mitral annulus (black arrowhead). (b) Corresponding TEE image (two-chamber view at 0°) similarly shows both foci of calcification (white and black arrowheads), which cause acoustic shadowing. (c) Oblique CT reconstruction through long axis of LV and LA shows posterior leaflet prolapse (arrowhead). (d) TEE image (two-chamber view at 0°) similarly shows a flail posterior leaflet (arrowhead) with cordal rupture. A rupture of tendinous cords (as verified during surgery) was suspected but could not be directly demonstrated with CT.

 


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  		Figure 5c: (a) Oblique CT image through long axis of LV and LA (at 5% of the R-R interval) shows grade I (>2 but ≤5 mm) calcification of the anterior leaflet (white arrowhead) and grade II (>5 mm) calcification of the posterior mitral annulus (black arrowhead). (b) Corresponding TEE image (two-chamber view at 0°) similarly shows both foci of calcification (white and black arrowheads), which cause acoustic shadowing. (c) Oblique CT reconstruction through long axis of LV and LA shows posterior leaflet prolapse (arrowhead). (d) TEE image (two-chamber view at 0°) similarly shows a flail posterior leaflet (arrowhead) with cordal rupture. A rupture of tendinous cords (as verified during surgery) was suspected but could not be directly demonstrated with CT.

 


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  		Figure 5d: (a) Oblique CT image through long axis of LV and LA (at 5% of the R-R interval) shows grade I (>2 but ≤5 mm) calcification of the anterior leaflet (white arrowhead) and grade II (>5 mm) calcification of the posterior mitral annulus (black arrowhead). (b) Corresponding TEE image (two-chamber view at 0°) similarly shows both foci of calcification (white and black arrowheads), which cause acoustic shadowing. (c) Oblique CT reconstruction through long axis of LV and LA shows posterior leaflet prolapse (arrowhead). (d) TEE image (two-chamber view at 0°) similarly shows a flail posterior leaflet (arrowhead) with cordal rupture. A rupture of tendinous cords (as verified during surgery) was suspected but could not be directly demonstrated with CT.

 
Mitral Valve Surgery and Pathologic Results
Mitral valve repair techniques included ring annuloplasty in eight of nine patients. Five of these eight patients additionally underwent partial resection of the posterior leaflet. One patient underwent mechanical valve replacement. Ruptured tendinous cords were detected intraoperatively in four patients, including the three patients in whom cord rupture was detected preoperatively with TEE. Leaflet thickening that corresponded to preoperative findings at TEE and multi–detector row CT was demonstrated intraoperatively in all nine patients. Of the five patients who were observed to have annulus calcification intraoperatively, one had severe calcification and underwent mechanical valve replacement. These findings corresponded exactly to the preoperative findings at TEE and multi–detector row CT. Similarly, valve prolapse, as demonstrated preoperatively with TEE and multi–detector row CT, was found intraoperatively in eight patients. Histopathologic examination of the resected posterior leaflet segments in five patients revealed myxoid degeneration with focal fibrosis and necrosis and some areas of dystrophic calcification. The mitral valve that was replaced in one patient showed extensive areas of myxoid degeneration and fibrosis on the anterior and posterior leaflet and severe calcification of the mitral annulus, similar to the findings at TEE and multi–detector row CT.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
Three entities describing the degree of mitral regurgitation can be quantified with echocardiography: regurgitant volume, regurgitant fraction, and effective regurgitant orifice. The latter of these entities is the most important echocardiographic marker of lesion severity (5,25). Direct visualization of the ROA with transthoracic echocardiography or TEE is, however, almost impossible (19); therefore, indirect estimations of the effective regurgitant orifice are derived from calculations of regurgitant flow rates and peak flow velocities (11). To the best of our knowledge, our study results demonstrate for the first time that retrospectively ECG-gated 16–detector row CT is feasible for directly visualizing and measuring the ROA, enabling a grading of mitral regurgitation severity similar to that enabled by echocardiography and ventriculography. Moreover, multi–detector row CT can provide detailed information about underlying morphologic abnormalities such as annulus calcification, leaflet thickening, and valve prolapse and can thus indicate the possible cause and mechanism of mitral regurgitation.

Grading of Mitral Regurgitation
Several echocardiographic techniques have been applied for grading mitral regurgitation. These techniques include assessment of the area and direction of color Doppler jets (11), assessment of the continuous-wave Doppler envelope of the mitral regurgitation signal (26), assessment of alterations in pulmonary venous flow (20), quantitative measurement of the LV inflow and outflow volume and the velocity time integral of the regurgitant flow (11), the flow convergence method (18), calculations performed by using the continuity equation (11), and measurement of the vena contracta (19). This considerable number of methods partly reflects the inherent complexity of echocardiographic mitral regurgitation grading, which requires considerable operator skills, exact geometric alignment, and repetitive measurements to minimize errors and depends on patient morphologic characteristics, instrumental settings, and transducer position. Any of these factors may combine to lead the unwary to the wrong conclusion regarding lesion severity (11).

Magnetic resonance imaging has been shown to be useful in quantifying mitral regurgitation by enabling a calculation of LV inflow minus LV outflow; however, this method is limited by the difficulty inherent in correcting the position of the control volume for mitral valve motion (27).

Cardiac catheterization is the traditional method for assessing the severity of mitral regurgitation on the basis and persistence of LA opacification. Although this method is time honored, it has limitations, such as leading to a false estimation of stroke volumes and fractions (11) and being subject to a wide variation in regurgitant flow within each ventriculographic grade and a substantial overlap of regurgitant volume indexes between grades (12).

In the present study, a strong correlation between ROA size at multi–detector row CT and the degree of mitral regurgitation was found; this indicates that CT is valuable for assessing the severity of the disease. In contrast to echocardiography, with multi–detector row CT, the regurgitant orifice can be directly visualized and measured because multiplanar reconstructions can be created in any desired plane. The observed nonsignificant differences between some ROA values when either TEE or ventriculography was used as a standard of reference may have resulted from the fact that hemodynamic parameters cannot be assessed with CT. Another explanation could be that the optimal phase during systole that showed the largest ROA at CT was missed. Also, the sample size of 19 patients may have been too small to yield statistically significant differences between grades.

Morphologic Valve Abnormalities
When mitral regurgitation is detected, it is important not only to make an assessment of its severity but also to make a judgment regarding the underlying cause. In our study, multi–detector row CT was shown to accurately depict the common morphologic abnormalities of the valvular apparatus associated with mitral regurgitation, to enable an analysis of the possible underlying mechanism of regurgitation, and to have the potential to clarify the cause of regurgitation (degenerative lesions with leaflet prolapse, rheumatic lesions with thickened valves, or endocarditis with leaflet vegetations). Excellent agreement as to the presence and degree of mitral annulus calcification and leaflet thickening was achieved between multi–detector row CT, TEE, and surgery. Additionally, prolapse of one or both valve leaflets was correctly diagnosed with multi–detector row CT in all patients. The only morphologic abnormality that was missed at multi–detector row CT was rupture of the tendinous cords in four patients. The presently insufficient visualization of tendinous cords with multi–detector row CT will hopefully be overcome with recent scanner developments that result in higher temporal and spatial resolution (28).

To assess additional clinical applications of multi–detector row CT, future studies should include patients with restricted valve motion and systolic anterior movement and patients with functional mitral regurgitation caused by annulus dilatation. However, assessment of patients with the latter condition would first require a definition of normal annulus physiology and motion throughout the cardiac cycle because considerable variations and discordant results regarding true mitral annulus dimensions in human subjects exist (29).

The following limitations of our study must be acknowledged. Only patients with coronary artery disease were included, which potentially could have led to an inclusion bias. Furthermore, the number of patients with mitral regurgitation (particularly considering the grade subgroups) was low, and the number of patients with morphologic valve abnormalities was small. Therefore, the statistical power of our results is limited, and data from a larger patient population with mitral regurgitation are needed to determine if use of this technique has the potential to become a clinical reality. Another drawback was the applied radiation dose inherent with the CT technique. However, the CT data set in this study was not used just for mitral valve imaging but was primarily used for assessing coronary arteries, and the same data may be used to quantify ventricular ejection fraction. Finally, results of TEE and ventriculographic assessment of mitral regurgitation were semiquantitative, which enabled only nonparametric statistical comparisons between the CT data and the TEE and ventriculographic data. Further prospective studies should aim at a direct comparison of quantitative data from both echocardiography and multi–detector row CT.

In conclusion, planimetric measurement of the ROA with 16–detector row CT enables a grading of mitral regurgitation that is similar to the grading of mitral regurgitation at TEE and ventriculography. Multi–detector row CT is further able to depict morphologic valve abnormalities, thus yielding information about the possible underlying cause and mechanism of regurgitation. The results of our study expand the role of multi–detector row CT; it can now be considered a modality that can enable evaluation of not only coronary arteries and ventricular functional parameters but also mitral valve disease.


   FOOTNOTES
 

Abbreviations: ECG = electrocardiography • LA = left atrium • LV = left ventricle • ROA = regurgitant orifice area • TEE = transesophageal echocardiography

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, H.A., S.W., B.M., T.B.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, H.A., S.L.; clinical studies, all authors; statistical analysis, H.A.; and manuscript editing, H.A., S.W., D.A.B., A.P., B.B., L.M.D., B.M., T.B.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Jones EC, Devereux RB, Roman MJ, et al. Prevalence and correlates of mitral regurgitation in a population-based sample (the Strong Heart Study). Am J Cardiol 2001;87:298–304.[CrossRef][Medline]
  2. Carabello BA, Crawford FA Jr. Valvular heart disease. N Engl J Med 1997;337:32–41.[Free Full Text]
  3. Zoghbi WA, Enriquez-Sarano M, Foster E, et al. Recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography. J Am Soc Echocardiogr 2003;16:777–802.[CrossRef][Medline]
  4. Cheitlin MD, Alpert JS, Armstrong WF, et al. ACC/AHA Guidelines for the Clinical Application of Echocardiography: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Clinical Application of Echocardiography)—developed in collaboration with the American Society of Echocardiography. Circulation 1997;95:1686–1744.[Free Full Text]
  5. Irvine T, Li XK, Sahn DJ, Kenny A. Assessment of mitral regurgitation. Heart 2002;88(suppl 4):iv11–iv19.[Free Full Text]
  6. Enriquez-Sarano M, Seward JB, Bailey KR, Tajik AJ. Effective regurgitant orifice area: a noninvasive Doppler development of an old hemodynamic concept. J Am Coll Cardiol 1994;23:443–451.[Abstract]
  7. Dujardin KS, Enriquez-Sarano M, Bailey KR, Nishimura RA, Seward JB, Tajik AJ. Grading of mitral regurgitation by quantitative Doppler echocardiography: calibration by left ventricular angiography in routine clinical practice. Circulation 1997;96:3409–3415.[Abstract/Free Full Text]
  8. Smith MD. Evaluation of valvular regurgitation by Doppler echocardiography. Cardiol Clin 1991;9:193–228.[Medline]
  9. Sellers RD, Levy MJ, Amplatz K, Lillehei CW. Left retrograde cardioangiography in acquired cardiac disease. Am J Cardiol 1964;14:437–447.[CrossRef][Medline]
  10. Grossman W. Profiles in valvular heart disease. In: Baim DS, Grossman W, eds. Cardiac catheterization, angiography, and intervention. 4th ed. Philadelphia, Pa: Lea & Febiger, 1991; 557–581.
  11. Wiegers SE, Herrmann HC, Plappert T, Sutton MG. Valvular heart disease. In: Sutton MGSJ, Rutherford JD, eds. Clinical cardiovascular imaging: a companion to Braunwald's heart disease. Philadelphia, Pa: Elsevier-Saunders, 2004; 280–338.
  12. Croft CH, Lipscomb K, Mathis K, et al. Limitations of qualitative angiographic grading in aortic or mitral regurgitation. Am J Cardiol 1984;53:1593–1598.[CrossRef][Medline]
  13. Achenbach S, Ulzheimer S, Baum U, et al. Noninvasive coronary angiography by retrospectively ECG-gated multislice spiral CT. Circulation 2000;102:2823–2828.[Abstract/Free Full Text]
  14. Boehm T, Alkadhi H, Roffi M, et al. Time-effectiveness, observer-dependence, and accuracy of measurements of left ventricular ejection fraction using 4-channel MDCT. Rofo 2004;176:529–537.[Medline]
  15. Willmann JK, Kobza R, Roos JE, et al. ECG-gated multi–detector row CT for assessment of mitral valve disease: initial experience. Eur Radiol 2002;12:2662–2669.[Medline]
  16. Schmidlin D, Bettex D, Bernard E, et al. Transoesophageal echocardiography in cardiac and vascular surgery: implications and observer variability. Br J Anaesth 2001;86:497–505.[Abstract/Free Full Text]
  17. Shanewise JS, Cheung AT, Aronson S, et al. ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesth Analg 1999;89:870–884.[Free Full Text]
  18. Recusani F, Bargiggia GS, Yoganathan AP, et al. A new method for quantification of regurgitant flow rate using color Doppler flow imaging of the flow convergence region proximal to a discrete orifice: an in vitro study. Circulation 1991;83:594–604.[Abstract/Free Full Text]
  19. Hall SA, Brickner ME, Willett DL, Irani WN, Afridi I, Grayburn PA. Assessment of mitral regurgitation severity by Doppler color flow mapping of the vena contracta. Circulation 1997;95:636–642.[Abstract/Free Full Text]
  20. Kamp O, Huitink H, van Eenige MJ, Visser CA, Roos JP. Value of pulmonary venous flow characteristics in the assessment of severity of native mitral valve regurgitation: an angiographic correlated study. J Am Soc Echocardiogr 1992;5:239–246.[Medline]
  21. Flohr T, Bruder H, Stierstorfer K, Simon J, Schaller S, Ohnesorge B. New technical developments in multislice CT. II. Sub-millimeter 16-slice scanning and increased gantry rotation speed for cardiac imaging. Rofo 2002;174:1022–1027.
  22. Adler Y, Fink N, Spector D, Wiser I, Sagie A. Mitral annulus calcification: a window to diffuse atherosclerosis of the vascular system. Atherosclerosis 2001;155:1–8.[CrossRef][Medline]
  23. Cohen J. A coefficient of agreement for nominal scales. Educ Psychol Meas 1960;20:37–46.[CrossRef]
  24. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159–174.[CrossRef][Medline]
  25. Reimold SC, Ganz P, Bittl JA, et al. Effective aortic regurgitant orifice area: description of a method based on the conservation of mass. J Am Coll Cardiol 1991;18:761–768.[Abstract]
  26. Utsunomiya T, Patel D, Doshi R, Quan M, Gardin JM. Can signal intensity of the continuous wave Doppler regurgitant jet estimate severity of mitral regurgitation? Am Heart J 1992;123:166–171.[CrossRef][Medline]
  27. Fujita N, Chazouilleres AF, Hartiala JJ, et al. Quantification of mitral regurgitation by velocity-encoded cine nuclear magnetic resonance imaging. J Am Coll Cardiol 1994;23:951–958.[Abstract]
  28. Flohr T, Stierstorfer K, Raupach R, Ulzheimer S, Bruder H. Performance evaluation of a 64-slice CT system with z-flying focal spot. Rofo 2004;176:1803–1810.[Medline]
  29. Timek TA, Miller DC. Experimental and clinical assessment of mitral annular area and dynamics: what are we actually measuring? Ann Thorac Surg 2001;72:966–974.[Abstract/Free Full Text]




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