DOI: 10.1148/radiol.2453061953
(Radiology 2008;246:110-115.)
© RSNA, 2008
Saline Flush Effect for Enhancement of Aorta and Coronary Arteries at Multidetector CT Coronary Angiography1
Dae Jung Kim, MD,
Tae Hoon Kim, MD,
Sang Jin Kim, MD,
Dong Phil Kim, RT,
Chi Suk Oh, RT,
Young Hoon Ryu, MD,
Young Jin Kim, MD, and
Byoung Wook Choi, MD
1 From the Department of Radiology, Yonsei University College of Medicine, Seoul, South Korea. Received November 16, 2006; revision requested January 18, 2007; revision received February 4; accepted March 7; final version accepted May 22.
Address correspondence to T.H.K., Department of Radiology, Yongdong Severance Hospital, 146-92 Dogok-Dong, Kangnam-Gu, Seoul 135-720, South Korea (e-mail: thkim1{at}yumc.yonsei.ac.kr).
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ABSTRACT
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Purpose: To prospectively investigate the effect of the injection rate of a saline solution as a bolus chaser for the enhancement of the aorta and coronary arteries at multidetector computed tomographic (CT) coronary angiography.
Materials and Methods: Institutional review board approved this study, and all patients gave informed consent. One hundred consecutive patients (59 men, 41 women; mean age, 58 years ± 11 [standard deviation]) underwent 64-section CT coronary angiography for coronary artery disease. They were divided into five groups (each group, n = 20) according to the injection rate of saline solution (3, 4, 5, 6, and 7 mL/sec). Iodinated contrast medium (60 mL) was injected intravenously at a rate of 4 mL/sec, followed by 60 mL saline solution administered intravenously at a rate of 3–7 mL/sec, depending on the groups. Attenuation values of the aortic root, right coronary artery, left anterior descending artery, and left circumflex artery were measured. Analysis of variance with the Scheffé method was used to evaluate statistical significance of the differences in attenuation according to the injection rate of saline solution.
Results: The degree of contrast enhancement was affected by the injection rate of saline solution, and the attenuation values were higher as the injection rate increased up to 4–5 mL/sec (P < .05). The values plateaued at rates over 5 mL/sec in the aorta and over 4 mL/sec in the coronary arteries.
Conclusion: An injection rate of 4–5 mL/sec as a saline solution chaser is optimal for achieving maximum attenuation values of the aorta or coronary arteries by using 64-section CT with 60 mL contrast material.
© RSNA, 2008
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INTRODUCTION
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The use of a saline solution injected intravenously immediately after bolus injection of contrast material, also known as a bolus chaser, has been reported to allow a substantial reduction of contrast media volume with vascular attenuation comparable to that obtained with larger volumes of contrast media (1,2). It is expected that the use of a bolus chaser would also allow volume reduction of contrast material at multidetector computed tomography (CT) coronary angiography (3,4). However, to the best of our knowledge, the effect of the injection rate of saline solution as a bolus chaser on vascular enhancement during multidetector CT coronary angiography has not been previously studied. Thus, the objective of this study was to prospectively investigate the effect of the injection rate of a saline solution as a bolus chaser for the enhancement of the aorta and coronary arteries at multidetector CT coronary angiography.
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MATERIALS AND METHODS
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Patients
In August and September 2005, 100 consecutive patients undergoing multidetector CT coronary angiography for suspected coronary artery disease were prospectively enrolled in this study. This study was approved by the institutional review boards of the Yonsei University Medical Center, Korea; informed consent was obtained. Of 100 patients, 59 were men and 41 were women. Their mean age at the time of examination was 58 years (age range, 37–82 years). Body weight ranged from 51 to 83 kg (mean, 64 kg).
Patients were consecutively divided into five groups, with different protocols for intravenous administration of 60 mL saline solution: group 1 at a rate of 3 mL/sec (n = 20), group 2 at a rate of 4 mL/sec (n = 20), group 3 at a rate of 5 mL/sec (n = 20), group 4 at a rate of 6 mL/sec (n = 20), and group 5 at a rate of 7 mL/sec (n = 20).
Multidetector CT
Multidetector CT coronary angiography was performed by using a 64-section helical scanner (Somatom Sensation 64; Siemens Medical Solutions, Forchheim, Germany). Prior to the examination, the patients' heart rates were measured. A β-blocker (40 mg propranolol hydrochloride; Pranol, Dae Woong, Seoul, Korea) was administered orally 1–2 hours before the examination to reduce the heart rate in patients with a heart rate greater than 65 beats per minute. In all patients, electrocardiographic traces were recorded simultaneously. The study was performed in some patients (n = 18) with continued rate greater than 65 beats per minute despite administration of a β-blocker. The mean heart rate during the scan was 41–79 beats per minute (mean, 58 beats per minute; median, 57 beats per minute).
Imaging was performed during suspended full inspiration by using a real-time bolus-tracking technique (CARE; Siemens Medical Solutions). A region of interest (ROI) was drawn (D.P.K. or C.S.O.) eccentrically apart from the superior vena cava on the ascending aorta to avoid streak artifacts caused by high concentration of contrast material. Sixty milliliters of iodinated contrast medium (Xenetix 350; Guerbet, France) was administrated intravenously with a dual-head injector (Envision CT; Medrad, Warrendale, Pa) at a rate of 4 mL/sec for 15 seconds. Sixty milliliters of saline solution was injected at a rate of 3–7 mL/sec, according to the groups, immediately after the injection of contrast medium was completed. The scans were started 5 seconds after a threshold trigger of 100 HU was reached. Scan delay ranged from 20 to 27 seconds (mean, 23 seconds). Mean scan time was 12 seconds (time range, 11–14 seconds). The following scan parameters were used: 370-msec gantry rotation, 120 kVp, 700 mAs, 0.6-mm section collimation, 3-mm section width, and 4.6-mm table feed per rotation. Scans and bolus timing procedures were successfully completed in all patients. There was no extravasation of contrast material or saline solution.
Image reconstruction was performed on the scanner's workstation by using commercially available software (Syngo CT2006A-W, Somaris/5; Siemens Medical Solutions). We used the partial scan algorithm, which provided a heart rate–dependent temporal resolution between 94 and 185 msec from a 370-msec gantry rotation. To acquire images of least motion, we reconstructed the image set at the selected phase, where the right coronary artery (RCA) was conspicuously visualized without a motion artifact at its middle segment. This was selected on the basis of retrospective electrocardiographic triggering after review of the preview image series by one of two technologists (D.P.K. and C.S.O.) who had 4 years of experience in cardiac CT. The reconstruction parameters were as follows: 0.6-mm section thickness, 0.4-mm increment, 512 x 512-pixel image matrix, medium smooth kernel (B25f), and 18–20-cm field of view.
CT Data Analysis
The images were evaluated by two reviewers (D.J.K. and T.H.K., with 2 and 13 years of experience in cardiac imaging interpretation, respectively) in consensus at a workstation. Transverse and oblique coronal or sagittal sections in the dataset were selected to measure the attenuation value, in Hounsfield units, of the aorta near the aortic annulus and the proximal and middle segments of three coronary arteries: RCA, left anterior descending artery (LAD), and left circumflex artery (LCX) (Figs 1, 2). The ROI was drawn with a circle as large as possible in the coronary arteries, and calcifications, plaques, and stenosis were avoided. We used the mean values based on two measurements obtained from two ROIs in each segment. The size of each coronary artery was also measured in the ROI drawing sites on the transverse, oblique coronal, or sagittal images.
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Figure 1a: Assessment of mean attenuation in aorta and proximal and middle segments of three coronary arteries at coronary CT angiography in a 63-year-old woman. (a) Oblique transverse maximum intensity projection shows ROIs to assess mean attenuation at the aorta (ROI1) and proximal segment of RCA (ROI2). (b) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI2 and ROI4) and distal (ROI3 and ROI5) segments of RAD and LCX. (c) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI6) and distal (ROI7) segments of LAD.
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Figure 1b: Assessment of mean attenuation in aorta and proximal and middle segments of three coronary arteries at coronary CT angiography in a 63-year-old woman. (a) Oblique transverse maximum intensity projection shows ROIs to assess mean attenuation at the aorta (ROI1) and proximal segment of RCA (ROI2). (b) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI2 and ROI4) and distal (ROI3 and ROI5) segments of RAD and LCX. (c) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI6) and distal (ROI7) segments of LAD.
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Figure 1c: Assessment of mean attenuation in aorta and proximal and middle segments of three coronary arteries at coronary CT angiography in a 63-year-old woman. (a) Oblique transverse maximum intensity projection shows ROIs to assess mean attenuation at the aorta (ROI1) and proximal segment of RCA (ROI2). (b) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI2 and ROI4) and distal (ROI3 and ROI5) segments of RAD and LCX. (c) Oblique coronal maximum intensity projection shows ROIs to assess mean attenuation at proximal (ROI6) and distal (ROI7) segments of LAD.
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Figure 2: Diagram with right anterior oblique projection shows areas measured for attenuation values at the aorta (Ao) and proximal and middle segments of coronary arteries. ROI is drawn with a circle as large as possible. Calcifications, plaques, and stenosis are avoided. The size of each coronary artery is also measured at ROI drawing sites.
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Statistical Analysis
Analysis of variance with the Scheffé method was used to evaluate the statistical significance of the differences in the patients' data among the groups for the enhancement degree of the aorta and coronary arteries, according to the injection rate of saline solution, mean scan delay and mean scan time, and the size of the coronary arteries among the RCA, LAD and LCX. Linear regression was used to determine the correlation between the enhancement degree and the size of coronary arteries. A P value less than .05 was considered to indicate a significant difference. The SPSS software (version 12.0; Statistical Package for the Social Science, Chicago, IL) was used for the statistical evaluations.
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RESULTS
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Age, weight, mean heart rate during the scan, mean scan delay, and mean scan time were not significantly different among the groups (P > .05) (Table 1).
The mean attenuation values (Table 2) of the aorta (Fig 3a) were significantly different in groups 1 and 2 and those of the RCA (Fig 3b), LAD (Fig 3c), and LCX (Fig 3c) were significantly different in group 1 compared with other groups, according to the injection rate of saline solution (P < .05). There was a significant difference in mean attenuation between the LAD and the aorta. A statistically significant difference in mean attenuation was noted between the LCX and the aorta and RCA (P < .05) (Fig 4).
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Figure 3a: Graphs show mean attenuation values in aorta and coronary arteries according to injection rate of saline solution in 100 patients. (a) Mean attenuation is significantly different in groups 1 (3 mL/sec of saline solution) and 2 (4 mL/sec of saline solution) at the aorta (P < .05). (b–d) Mean attenuation is significantly different in group 1 (3 mL/sec of saline solution) at (b) RCA, (c) LAD, and (d) LCX (P < .05). Bars represent 2 standard deviations.
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Figure 3b: Graphs show mean attenuation values in aorta and coronary arteries according to injection rate of saline solution in 100 patients. (a) Mean attenuation is significantly different in groups 1 (3 mL/sec of saline solution) and 2 (4 mL/sec of saline solution) at the aorta (P < .05). (b–d) Mean attenuation is significantly different in group 1 (3 mL/sec of saline solution) at (b) RCA, (c) LAD, and (d) LCX (P < .05). Bars represent 2 standard deviations.
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Figure 3c: Graphs show mean attenuation values in aorta and coronary arteries according to injection rate of saline solution in 100 patients. (a) Mean attenuation is significantly different in groups 1 (3 mL/sec of saline solution) and 2 (4 mL/sec of saline solution) at the aorta (P < .05). (b–d) Mean attenuation is significantly different in group 1 (3 mL/sec of saline solution) at (b) RCA, (c) LAD, and (d) LCX (P < .05). Bars represent 2 standard deviations.
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Figure 3d: Graphs show mean attenuation values in aorta and coronary arteries according to injection rate of saline solution in 100 patients. (a) Mean attenuation is significantly different in groups 1 (3 mL/sec of saline solution) and 2 (4 mL/sec of saline solution) at the aorta (P < .05). (b–d) Mean attenuation is significantly different in group 1 (3 mL/sec of saline solution) at (b) RCA, (c) LAD, and (d) LCX (P < .05). Bars represent 2 standard deviations.
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Figure 4: Graph shows mean attenuation values at the aorta and each coronary artery in 100 patients. Mean attenuation at LAD is significantly lower than that at the aorta (P < .05). Mean attenuation at LCX is significantly lower than that at the aorta and RCA (P < .05). Bars represent 2 standard deviations.
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LCX was significantly smaller than the RCA and LAD (P < .05) (Table 3). The mean attenuation of the coronary arteries showed moderate correlation with the size of the arteries at the same sites (r = 0.369) (P < .01) (Fig 5).
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Figure 5: Linear regression between mean attenuation values and sizes of coronary arteries (slope, 32.936; correlation, 0.369; P < .01) (y = 237.164 + 32.936x, r = 0.369). Parallel lines represent 95% probability for values of the dependent variable.
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DISCUSSION
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To decrease the volume of contrast material during the shorter scan time, many researchers have studied saline chaser techniques. These techniques allow a substantial reduction of contrast material volume with vascular attenuation comparable to that obtained with a larger volume of contrast material (1,2,5–7). However, the studies have focused on the use of saline chaser immediately after injection of the contrast material by using a single- or dual-head power injector. Irie et al (6) described how varied amounts of saline solution were used to evaluate the time to peak aortic enhancement and the volume of contrast material saved.
In our study, we used variable injection rates of saline solution chaser. Our results showed that higher injection rates increased attenuation values of the aorta and coronary arteries. However, the attenuation values reached a plateau at rates over 5 mL/sec in the aorta and over 4 mL/sec in the coronary arteries. These findings suggest that injection rates greater than 5 mL/sec as a saline solution chaser are not helpful to increase the attenuation values of the aorta or coronary arteries. Therefore, with a fixed 60 mL amount of contrast material for a 64-section CT scanner, the proper injection rate as a saline solution chaser was 4–5 mL/sec to reach the maximum attenuation values of the aorta or coronary arteries. Higher injection rates of saline solution might cause poor opacification of the aorta or coronary arteries because the fixed contrast material passes too quickly. In our study, some patients had lower attenuation values at rates of 6 or 7 mL/sec.
Each coronary artery was measured at the proximal and middle segments. The LCX was significantly smaller than both the RCA and the LAD. In the evaluation of coronary artery disease, the small-sized vessels, such as branches or distal segments, were less enhanced. Possible explanations for the causes of lower enhancement were partial volume effect from the small-vessel sizes and poor opacification of the arteries due to small contrast material amount. In our study, the attenuation values measured in the coronary arteries showed moderate correlation with the size of the coronary arteries at the same sites. The size of the LCX was significantly smaller than that of the RCA and the LAD. However, the mean attenuation at the LCX was significantly lower than that at the RCA but not lower than that at the LAD. This finding suggests that, although we selected the least-motion phase for the RCA, the mean attenuation of the RCA may be increased due to more prominent motion artifacts than at the LAD.
A limitation of this study was that we did not perform the evaluation of attenuation values in the distal segments or small sizes of the coronary artery. Furthermore, we did not perform the evaluation of vessels with atherosclerotic disease, such as soft and calcified plaques, vessel stenosis, and vessel occlusions. These factors may affect the visualization capability of the vessels or the attenuation evaluation inside the vessels.
In conclusion, although the attenuation values are augmented as the injection rate of saline solution increases up to 4–5 mL/sec, the attenuation values plateau at injection rates over 5 mL/sec in the aorta and over 4 mL/sec in the coronary arteries. Therefore, by using 60 mL of 350 mg/mL iodinated contrast material at a rate of 4 mL/sec, the injection rate of 4–5 mL/sec as a saline solution chaser is optimal for achieving maximum attenuation values at the aorta or coronary arteries with a 64-section CT.
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ADVANCES IN KNOWLEDGE
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- The mean attenuation values in the coronary arteries and aorta were higher as the injection rate of saline solution increased up to 4–5 mL/sec, but the attenuation values plateaued at rates over 4 mL/sec in the coronary arteries and over 5 mL/sec in the aorta.
- The injection rate of 4–5 mL/sec as a saline solution chaser is optimal for achieving the maximum attenuation values in the coronary arteries or aorta.
- The mean attenuation values in the coronary arteries showed moderate correlation (r = 0.369) (P < .01) with the size of the arteries at the same sites.
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IMPLICATIONS FOR PATIENT CARE
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- An optimal flush rate of saline solution can reduce the required amount of contrast media.
- Achievement of maximum attenuation in the coronary arteries can improve image quality, which can provide more accurate diagnosis for suspected coronary disease.
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FOOTNOTES
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Abbreviations: LAD = left anterior descending artery • LCX = left circumflex artery • RCA = right coronary artery • ROI = region of interest
Guarantor of integrity of entire study, T.H.K.; 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, D.J.K., Y.J.K.; clinical studies, D.J.K., T.H.K., S.J.K., D.P.K., C.S.O.; statistical analysis, T.H.K.; and manuscript editing, T.H.K., S.J.K., Y.H.R., Y.J.K., B.W.C.
Authors stated no financial relationship to disclose.
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References
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- Haage P, Schmitz-Rode T, Hubner D, Piroth W, Gunther RW. Reduction of contrast material dose and artifacts by a saline flush using a double power injector in helical CT of the thorax. AJR Am J Roentgenol 2000;174:1049–1053. [Abstract/Free Full Text]
- Hopper KD, Mosher TJ, Kasales CJ, TenHave TR, Tully DA, Weaver JS. Thoracic spiral CT: delivery of contrast material pushed with injectable saline solution in a power injector. Radiology 1997;205:269–271. [Abstract/Free Full Text]
- Han JK, Kim AY, Lee KY, et al. Factors influencing vascular and hepatic enhancement at CT: experimental study on injection protocol using a canine model. J Comput Assist Tomogr 2000;24:400–406. [CrossRef][Medline]
- Yamashita Y, Komohara Y, Takahashi M, et al. Abdominal helical CT: evaluation of optimal doses of intravenous contrast material—a prospective randomized study. Radiology 2000;216:718–723. [Abstract/Free Full Text]
- Cademartiri F, Mollet N, van der Lugt A, et al. Non-invasive 16-row multislice CT coronary angiography: usefulness of saline chaser. Eur Radiol 2004;14:178–183. [CrossRef][Medline]
- Irie T, Kajitani M, Yamaguchi M, Itai Y. Contrast-enhanced CT with saline flush technique using two automated injectors: how much contrast medium does it save? J Comput Assist Tomogr 2002;26:287–291. [CrossRef][Medline]
- Dorio PJ, Lee FT Jr, Henseler KP, et al. Using a saline chaser to decrease contrast media in abdominal CT. AJR Am J Roentgenol 2003;180:929–934. [Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
