Radiology Cardiac Imaging

[Cardiac Imaging] Tissue Sodium Concentration in Myocardial Infarction in Humans: A Quantitative 23Na MR Imaging Study

2008-06-19

Purpose: To prospectively determine whether the absolute tissue sodium concentration (TSC) increases in myocardial infarctions (MIs) in humans and whether TSC is related to infarct size, infarct age, ventricular dysfunction, and/or electrophysiologic inducibility of ventricular arrhythmias.

Materials and Methods: Delayed contrast material–enhanced 1.5-T hydrogen 1 (¹H) magnetic resonance (MR) imaging was used to measure the size and location of nonacute MIs in 20 patients (18 men, two women; mean age, 63 years ± 9 [standard deviation]; age range, 48–82 years) examined at least 90 days after MI. End-systolic and end-diastolic volumes, ejection fraction, and left ventricle (LV) mass were measured with cine MR imaging. The TSC in normal, infarcted, and adjacent myocardial tissue was measured on sodium 23 (²³Na) MR images coregistered with delayed contrast-enhanced ¹H MR images. Programmed electric stimulation to induce monomorphic ventricular tachycardia (MVT) was used to assess arrhythmic potential, and myocardial TSC was compared between the inducible MVT and noninducible MVT patient groups.

Results: The mean TSC for MIs (59 µmol/g wet weight ± 10) was 30% higher than that for noninfarcted (remote) LV regions (45 µmol/g wet weight ± 5, P < .001) and that for healthy control subjects, and TSC did not correlate with infarct age or functional and morphologic indices. The mean TSC for tissue adjacent to the MI (50 µmol/g wet weight ± 6) was intermediate between that for the MI and that for remote regions. The elevated TSC measured in the MI at ²³Na MR imaging lacked sufficient contrast and spatial resolution for routine visualization of MI. Cardiac TSC did not enable differentiation between patients in whom MVT was inducible and those in whom it was not.

Conclusion: Absolute TSC is measurable with ²³Na MR imaging and is significantly elevated in human MI; however, TSC increase is not related to infarct age, infarct size, or global ventricular function. In regions adjacent to the MI, TSC is slightly increased but not to levels in the MI.

[Cardiac Imaging] Right Atrial Cavotricuspid Isthmus: Anatomic Characterization with Multi-Detector Row CT

2008-05-16

Purpose: To retrospectively evaluate the anatomic characteristics of the right atrial cavotricuspid isthmus (CTI) by using 64-section multi–detector row computed tomography (CT).

Materials and Methods: Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. The anatomic region of the CTI was evaluated in 201 patients (116 men and 85 women; mean age, 58 years ± 11 [standard deviation]) who underwent coronary multi–detector row CT. CTI length was assessed along three parallel isthmic levels (paraseptal, central, and inferolateral). Central isthmus depth was classified as straight (3 mm), concave (>3 to ≤5 mm), or pouchlike (>5 mm). Measurements were obtained during three cardiac phases: midsystole, middiastole, and atrial contraction. Subthebesian recess dimensions and eustachian ridge width were measured. Distances from the atrioventricular node artery to the coronary sinus, from the right coronary artery (RCA) to the inferior vena cava, and from the RCA to the tricuspid valve annulus were measured. Software was used for statistical analysis.

Results: At middiastole, the paraseptal isthmus (mean length, 20 mm ± 3.5; range, 11–34 mm) was significantly shorter than the central isthmus (24 mm ± 4.3; range, 12–43 mm) and the central isthmus was shorter than the inferolateral isthmus (27 mm ± 4.8; range, 13–45 mm) (P < .001). The longest CTI measurements were obtained during midsystole, and the shortest were obtained during atrial contraction (40% variation per cardiac cycle). Isthmus contraction occurred primarily in the posterior segment of the central isthmus (RCA to inferior vena cava distance). At middiastole, the central isthmus was straight in 8% of patients, concave in 47% of patients, and pouchlike (>5 mm) in 45% of patients. The mean depth was greater during atrial contraction (6.3 mm ± 2.1) than in midsystole (4.3 mm ± 1.5) and middiastole (5.1 mm ± 1.8) (32% variation during cardiac cycle). A subthebesian recess greater than 5 mm deep was identified in 45% of patients. In 24% of patients, a thick eustachian ridge greater than 4 mm was seen. The atrioventricular node artery passed close to the coronary sinus wall (mean distance, 2.1 mm ± 0.7; range, 1–6 mm).

Conclusion: Cardiac multi–detector row CT provides extensive information regarding the size and morphology of the CTI and its related structures.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/247/3/658/DC1

[Cardiac Imaging] Coronary Calcium Coverage Score: Determination, Correlates, and Predictive Accuracy in the Multi-Ethnic Study of Atherosclerosis

2008-05-16

Purpose: To develop a new calcium score for use with unenhanced cardiac computed tomography (CT) that can be used to define the percentage of coronary arteries affected by calcium and to correlate this score with risk factors and cardiovascular events.

Materials and Methods: Institutional review boards at all participating centers approved this HIPAA-compliant study, and all participants gave written informed consent. Calcium coverage score (CCS), which represents the percentage of coronary arteries affected by calcific plaque, was calculated for 3252 participants in the Multi-Ethnic Study of Atherosclerosis in whom calcific plaque was detected with CT. Quasi-Poisson models were used to estimate associations (assessed by using t tests with robust standard errors) between CCS and risk factors. Associations between the CCS, Agatston, and calcium mass scores (hereafter, mass scores) and outcomes were estimated and assessed by using Cox proportional hazards models with Wald tests. The predictive ability of these models was assessed by using area under the receiver operating characteristic curves and bootstrap t tests.

Results: After adjustments were made for age, race, ethnicity, and sex in the quasi-Poisson model, CCS was associated with hypertension, dyslipidemia, and diabetes (P < .001 for all diseases). After adjustments for age and sex, a twofold increase in CCS was associated with a 52% (95% confidence interval: 34%, 72%) increase in risk for any coronary heart disease (CHD) event. When Agatston or mass scores were included with CCS in a Cox model for prediction of CHD events, neither Agatston score nor mass score was a significant predictor, whereas CCS remained significantly associated with CHD events. Although receiver operating characteristic curves suggested that there was a difference between CCS score and Agatston and mass scores in prediction of a cardiac event, no differences in prediction of hard cardiac events (myocardial infarction, death) were found.

Conclusion: Both spatial distribution and amount of calcified plaque contribute to risk for CHD.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2473071469/DC1

[Cardiac Imaging] Dual-Source CT: Effect of Heart Rate, Heart Rate Variability, and Calcification on Image Quality and Diagnostic Accuracy

2008-04-22

Purpose: To prospectively evaluate the effect of heart rate, heart rate variability, and calcification on dual-source computed tomography (CT) image quality and to prospectively assess diagnostic accuracy of dual-source CT for coronary artery stenosis, by using invasive coronary angiography as the reference standard.

Materials and Methods: This study had local Ethics Committee approval; all patients gave informed consent. Patients who underwent bypass surgery were excluded; patients with coronary artery stent-grafts were included. One hundred patients (20 women, 80 men; mean age, 62 years ± 10 [standard deviation]) known to have or suspected of having coronary artery disease underwent dual-source CT and invasive coronary angiography. Image quality was assessed. Accuracy of dual-source CT in depiction or exclusion of significant stenosis (≥50%) was evaluated on a per-segment and per-patient basis. Effects of heart rate, heart rate variability, and calcification on image quality and accuracy were analyzed by using multivariate regression and were analyzed between subgroups of predictor variables. Simple regression was performed to calculate thresholds for adequate image quality.

Results: Mean heart rate was 64.9 beats per minute ± 13.2, mean variability was 23.6 beats per CT examination ± 36.2, and mean Agatston score was 786.5 ± 965.9. Diagnostic image quality was obtained in 90.2% of segments. Sensitivity, specificity, and positive and negative predictive values for the presence of significant stenosis were, respectively, 91.1%, 92.0%, 75.4%, and 97.5% by segment and 100%, 81.5%, 93.6%, and 100% by patient. Image quality was significantly related to heart rate variability (P = .015) and calcification (P < .001); the number of nondiagnostic segments was significantly affected by calcification only. Calcification was the single factor with significant impact on diagnostic accuracy (P = .001).

Conclusion: While dual-source CT resulted in heart-rate independent image quality, image quality remained prone to heart rate variability and calcification.

[Cardiac Imaging] Right Heart: Split-Bolus Injection of Diluted Contrast Medium for Visualization at Coronary CT Angiography

2008-04-22

Purpose: To retrospectively compare a split-bolus contrast medium injection protocol with a biphasic and a monophasic protocol in terms of visualization of the right and left heart, contrast medium–related streak artifacts, and level of attenuation in the cardiac chambers and coronary arteries at coronary computed tomographic (CT) angiography.

Materials and Methods: The human research committee approved this HIPAA-compliant study and waived informed consent. Seventy-five patients had undergone 64-section coronary CT angiography: 25 were injected by using a monophasic, contrast-medium-only protocol with a single-syringe injector; 25 were injected by using a biphasic protocol with a dual-syringe injector; and 25 were injected by using a split-bolus protocol with a dual-syringe injector and an initial bolus of contrast medium followed by 50 mL of a 70%:30% saline-to–contrast medium mixture and a 30-mL saline chaser. Two radiologists rated the visualization of right and left heart structures and the degree of streak artifacts. One observer performed attenuation measurements of the cardiac chambers and of the coronary arteries. Data were analyzed with one-way analysis of variance and Duncan post-hoc multiple comparison procedures.

Results: Data for 27 women and 48 men (mean age, 62 years) were included. Mean contrast medium attenuation in the right heart was significantly (P < .001) higher in the split-bolus group than in the biphasic injection group but was significantly (P < .001) lower than in the monophasic injection group. For the left heart and the coronary arteries, there were no significant differences among the three groups. Artifacts occurred less frequently (P < .001) in the biphasic and split-bolus groups than in the monophasic group. Visualization of right heart structures was rated significantly (P < .05) better in the split-bolus group than in the two other groups, while there was no difference for visualization of left heart structures.

Conclusion: Split-bolus injection provides sufficient attenuation for visualization of the right heart, while streak artifacts from high-attenuation contrast material can generally be avoided and arterial attenuation is maintained.

[Cardiac Imaging] Reperfused Myocardial Infarction: Contrast-enhanced 64-Section CT in Comparison to MR Imaging

2008-03-27

Purpose: To prospectively compare 64-section multidetector computed tomography (CT) and cardiac magnetic resonance (MR) imaging for the early assessment of myocardial enhancement and infarct size after acute reperfused myocardial infarction (MI).

Materials and Methods: The study was HIPAA compliant and was approved by the institutional review board. All participants gave written informed consent. Twenty-one patients (18 men; mean age, 60 years ± 13 [standard deviation]) were examined with 64-section multidetector CT and cardiac MR imaging 5 days or fewer after a first reperfused MI. Multidetector CT was performed during the first pass of contrast material to assess myocardial perfusion and detect microvascular obstruction (no reflow). In 15 patients, a second scan was performed 7 minutes later to assess total infarct size by using delayed hyperenhancement. Early hypoenhancement and delayed hyperenhancement were compared between multidetector CT and cardiac MR imaging with Pearson correlation coefficient and Bland-Altman analysis.

Results: Early hypoenhancement was recognized on all multidetector CT and cardiac MR images. Delayed hyperenhancement was observed with cardiac MR imaging at all examinations and with multidetector CT at 11 of 15 examinations. While signal intensity differences between hypoperfused and normal myocardium were comparable for first-pass multidetector CT and cardiac MR imaging, cardiac MR imaging had a far better contrast-to-noise ratio (CNR) for delayed acquisitions than did CT (P < .001). Hypoenhanced areas (as a percentage of left ventricular mass) at first-pass multidetector CT (11% ± 6) correlated well with those at first-pass cardiac MR imaging (7% ± 4, R² = 0.72). Delayed-enhancement multidetector CT (13% ± 9) correlated well with delayed-enhancement cardiac MR imaging (15% ± 7, R² = 0.55). Quantification of delayed hypoenhancement (n = 12) had very good correlation between multidetector CT (4% ± 4) and cardiac MR imaging (3% ± 2) (R² = 0.85).

Conclusion: Early and late hypoenhancement showed good CNR and correlated well between multidetector CT and cardiac MR imaging.

[Cardiac Imaging] Diagnostic Performance of Myocardial Perfusion MR at 3 T in Patients with Coronary Artery Disease

2008-03-27

Purpose: To prospectively determine the diagnostic performance of myocardial perfusion magnetic resonance (MR) imaging at 3 T for helping depict clinically relevant coronary artery stenosis (≥50% diameter) in patients with suspected or known coronary artery disease (CAD), with coronary angiography as the reference standard.

Materials and Methods: The study was approved by the local ethics committee; written informed consent was obtained. Vasodilator stress perfusion imaging by using a turbo field-echo sequence was obtained in 101 patients (71 men, 30 women; mean age, 62 years ± 7.7 [standard deviation]) scheduled for coronary angiography. Myocardial ischemia was defined as stress-inducible perfusion deficit in arterial territories without delayed enhancement (DE) or additional stress-inducible perfusion deficit in territories with nontransmural DE. Images were evaluated in consensus by two blinded readers. Diagnostic performance was determined on per-patient and per–coronary artery territory bases. The number of dark rim artifacts in patients without DE was determined in a second read. Interobserver variability was assessed in 40 randomly selected patients.

Results: One hundred one patients underwent MR examinations. Coronary angiography depicted relevant stenosis in 70 (69%) patients. Patient-based sensitivity and specificity were 90% and 71%, respectively. Sensitivity, specificity, and diagnostic accuracy for the detection of coronary stenosis in a specific territory were 76%, 89%, and 86%, respectively. In 24% of patients without DE, dark rim artifacts were detected, mostly in the left anterior descending artery territory (56%). In 40 randomly selected patients, there was agreement in the determination of myocardial perfusion deficits in 37 (93%, = 0.79) patients.

Conclusion: Myocardial perfusion MR imaging by using saturation-recovery spoiled gradient-echo imaging at 3 T has an accuracy of 84% for depicting hemodynamically relevant coronary artery stenosis in patients with suspected and known CAD.