Quantitative parameters of image quality in 64-slice computed tomography angiography of the coronary arteries

We explored quantitative parameters of image quality in consecutive patients undergoing 64-slice multi-detector computed tomography (MDCT) coronary angiography for clinical reasons. Forty-two patients (36 men, mean age 61 +/- 11 years, mean heart rate 63 +/- 10 bpm) underwent contrast-enhanced MDCT coronary angiography with a 64-slice scanner (Siemens Sensation 64, 64 mm x 0.6 mm collimation, 330 ms tube rotation, 850 mAs, 120 kV). Two independent observers measured the overall visualized vessel length and the length of the coronary arteries visualized without motion artifacts in curved multiplanar reformatted images. Contrast-to-noise ratio was measured in the proximal and distal segments of the coronary arteries. The mean length of visualized coronary arteries was: left main 12 +/- 6 mm, left anterior descending 149 +/- 25 mm, left circumflex 89 +/- 30 mm, and right coronary artery 161 +/- 38 mm. On average, 97 +/- 5% of the total visualized vessel length was depicted without motion artifacts (left main 100 +/- 0%, left anterior descending 97 +/- 6%, left circumflex 98 +/- 5%, and right coronary artery 95 +/- 6%). In 27 patients with a heart rate < or = 65 bpm, 98 +/- 4% of the overall visualized vessel length was imaged without motion artifacts, whereas 96+/-6% of the overall visualized vessel length was imaged without motion artifacts in 15 patients with a heart rate > 65 bpm (p < 0.001). The mean contrast-to-noise ratio in all measured coronary arteries was 14.6 +/- 4.7 (proximal coronary segments: range 15.1 +/- 4.4 to 16.1 +/- 5.0, distal coronary segments: range 11.4 +/- 4.2 to 15.9 +/- 4.9). In conclusion, 64-slice MDCT permits reliable visualization of the coronary arteries with minimal motion artifacts and high CNR in consecutive patients referred for non-invasive MDCT coronary angiography. Low heart rate is an important prerequisite for excellent image quality.     

Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multi-detector row CT.

The authors compared prospective (n = 20) and retrospective (n = 20) electrocardiography (ECG)-assisted multi-detector row computed tomography (CT) with non-ECG-assisted multi-detector row CT (n = 20) of the thoracic aorta with regard to reduction of motion-related artifacts. Image quality was rated for transverse source and sagittal oblique images of the thoracic aorta, including the aortic valve. ECG-assisted multi-detector row CT compared with non-ECG-assisted multi-detector row CT showed a significant reduction in motion artifacts for the entire thoracic aorta.     

The impact of motion artifacts on the reproducibility of repeated coronary artery calcium measurements

The purpose of this study is, using a 16-section multidetector-row helical computed tomography (MDCT) scanner with retrospective reconstruction, to compare variability in repeated coronary calcium scoring and qualitative scores of the motion artifacts. One hundred forty-four patients underwent two subsequent scans using MDCT. According to Agatston and volume algorithms, the coronary calcium scores during mid-diastole (the center corresponding to 70% of the R-R cycle) were calculated and the inter-scan variability was obtained. Motion artifacts from coronary artery calcium were subjectively evaluated and classified using a 5-point scale: 1, excellent; no motion artifacts; 2, fine, minor motion artifacts; 3, moderate, mild motion artifacts; 4, bad, severe motion artifacts; 5, poor, doubling or discontinuity. Each reading was done by vessels (left main, left descending, left circumflex and right coronary arteries) and the motion artifact score (mean of the scales) was determined per patient. The variability in the low (1.2+/-0.2) and high (2.4+/-0.6) motion artifact score groups was 7+/-6 (median, 6)% and 19+/-15 (16)% on the Agatston score (P<0.01) and 7+/-7 (6)% and 16+/-13 (14)% on the volume score (P<0.01), respectively. In conclusion, motion has a significant impact on the reproducibility of coronary calcium scoring.     

Report on the 86th Scientific Assembly and Annual Meeting of the Radiological Society of North America: motion artifact caused by heart pulsation observed on an electron beam and a multidetector-row CT

Recently developed technologies in CT imaging have allowed higher temporal resolution and less motion artifacts caused by heart pulsation. However, complete deletion of motion artifacts has not altogether been accomplished. In interpreting images, differentiation of motion artifacts and true lesion is essential. In this exhibition, the ascending aorta, outer contour of the heart, valve, lung adjacent to the heart, and other structures in the mediastinum are demonstrated focusing on the characteristics of motion artifact. Images obtained with an electron beam CT (Imatron 150XL) and a MDCT (LightSpeed QX/i, GEMS) are comparatively demonstrated. In electron beam CT, the temporal resolution ranged from 50 msec to 2,000 msec. In multidetector-row CT, half reconstruction algorithm (500 msec) and newly developed algorithm (130 msec) can be applied to reduce temporal resolution, although temporal resolution (800msec) of a full scan is fixed. Degree, shape, and site at which motion artifacts arise are analyzed with respect to the temporal resolution on two different CT systems. Learning objectives: Motion artifacts are correlated with the temporal resolution of the CT scanner. Electron beam and multidetector row CT provides different kinds of solutions to reduce motion artifacts.     

Evaluation of coronary stents and stenoses at different heart rates with dual source spiral CT (DSCT)

OBJECTIVES: Evaluation of coronary arteries at higher heart rates and in the presence of coronary stents remains problematic. The utilization of dual source computed tomography (DSCT) might improve the visualization of the coronary arteries under these conditions by imaging at a temporal resolution of 83 milliseconds, independent of heart rate. MATERIALS AND METHODS: Vessel phantoms (diameter 2-4 mm) were attached to a robotic device to simulate cardiac motion and scanned with a DSCT system. The phantoms had either inserts leading to 50% stenosis or carried stents. Images were evaluated for motion artifacts and measurements of the normal, stenotic, and in-stent lumen at different heart rates (50-120 bpm) were performed. Quantile regression analysis was performed to investigate heart rate dependence of the measurement errors. RESULTS: Visualization of the stenoses and stents was possible without motion artifacts at heart rates of up to 120 bpm. Image quality was similar for the static (0 bpm) and the dynamic (50-120 bpm) scans. Errors for diameter measurements of the vessel lumen and the stenotic lumen were low (3-mm vessel: 1-2%), but considerable for in-stent diameter measurements (3-mm stent: 27-32%). A window/level setting of 1500/300 Hounsfield units was more favorable for stent evaluation. No heart rate dependence was found. CONCLUSIONS: Depiction of coronary stents with DSCT is possible across a large range of simulated heart rates without motion artifacts and with image quality superior to that of previous generations of CT scanners.     

Malignant right coronary artery anomaly simulated by motion artifacts on MDCT

OBJECTIVE: The aim of our study was to determine the prevalence of anomalous right coronary artery imitation due to motion artifacts in MDCT. Routine chest MDCT for reasons other than cardiac or vascular imaging is usually performed using breath-hold technique but without retrospective ECG gating and consequently yields pulsating motion artifacts. A possible artifact in front of the aortic root imitates an anomalous right coronary artery originating from the left posterior sinus. This course of the right coronary artery is considered a malignant variant and raises the question of far-reaching consequences such as a bypass operation. SUBJECTS AND METHODS: We performed a prospective study involving 355 patients undergoing routine chest CT examinations. To determine the prevalence of anomalous right coronary artery imitation caused by this motion artifact, all images were evaluated prospectively by an experienced radiologist. RESULTS: Twenty-one patients (5.9%) were suspected of having a malignant variant of the right coronary artery. However, in all patients prior chest CT or additional coronary MR angiography showed a normal origin of the right coronary artery. CONCLUSION: Routine chest MDCT without retrospective ECG gating may produce artifacts around the aorta simulating a malignant variant of the right coronary artery. Considering the low incidence of this malignant interarterial variant, the need for routine chest CT examinations combined with ECG gating and further workup can be disputed from an economic point of view. This artifact should be known to avoid unnecessary further examinations.     

Noninvasive visualization of coronary arteries using contrast-enhanced multidetector CT: influence of heart rate on image quality and stenosis detection

OBJECTIVE: Although multidetector CT (MDCT) with retrospectively ECG-gated image reconstruction has been shown to permit noninvasive visualization of the coronary arteries, the 125-250 msec required for image acquisition frequently causes motion artifacts. We investigated the influence of a patient's heart rate on the presence of motion artifacts and on accuracy of stenosis detection on contrast-enhanced MDCT. MATERIALS AND METHODS: In 100 patients, MDCT was performed, and ECG-gated cross-sectional images were retrospectively reconstructed. From the 10 data sets obtained for each patient (reconstructed at 0-90% of the cardiac cycle in increments of 10%), we chose the best data set for every coronary artery. The images of the arteries were evaluated for occurrence of artifacts and the presence of high-grade stenosis (diameter reduction exceeding 70%) or occlusions. MDCT results were compared with coronary angiographic findings. RESULTS: Of the 400 coronary arteries, 115 (29%) could not be evaluated because of motion artifacts (n = 84) or other reasons (n = 31). Overall, 51 (49%) of 104 stenoses were revealed on MDCT. For detecting stenosis in those arteries that we could evaluate, MDCT had a sensitivity of 91% (51 of 56 stenoses detected) and a specificity of 89%. As the heart rate increased, the number of arteries that could be evaluated decreased, and overall sensitivity for stenosis detection decreased from 62% (heart rate < or = 70 beats per minute) to 33% (heart rate > 70 beats per minute). CONCLUSION: MDCT can reveal coronary stenoses, but the usefulness of MDCT as an aid in accurately evaluating stenoses decreases as a patient's heart rate increases.     

64层螺旋CT冠状动脉图像质量控制研究:最佳重组时相与心率关系

目的量化评估64层螺旋CT冠状动脉各分支不同重组时相图像质量,探讨冠状动脉CT成像最佳重组时相与心率关系。资料与方法102例患者均采用64层螺旋CT回顾性心电门控冠状动脉成像,男68例,女34例,平均年龄(58.1±9.7)岁,平均心率(66.4±11.5)次/min。心率<65次/min(n=43)为Ⅰ组,65～75次/min(n=34)为Ⅱ组,>75次/min(n=25)为Ⅲ组,每例患者的4支冠状动脉(左主干、左前降支、左回旋支、右冠状动脉)共分为12个节段用于图像质量分析。扫描原始数据以间隔5%在20%～80%时相分别回顾性重组冠状动脉图像,采用横断位、曲面重组、容积再现等方法对图像质量综合评分。结果Ⅰ组60%、65%和70%为最佳时相,Ⅱ组60%、65%时相为最佳时相,Ⅲ组右冠状动脉较优时相为35%、40%,左冠状动脉较优时相为60%、65%。结论心率和重组时相的选择是决定冠状动脉图像质量的重要因素。平均心率≤75次/min,冠状动脉各分支图像质量在心脏运动的舒张中期(60%、65%)最佳;>75次/min时,左右冠状动脉分别进行重组能明显提高冠状动脉的成像质量。     

Efficacy of pre-scan beta-blockade and impact of heart rate on image quality in patients undergoing coronary multidetector computed tomography angiography

OBJECTIVE: While beta-blockers are routinely administered to patients prior to coronary computed tomography angiography (CTA), their effectiveness is unknown. We therefore assessed the efficacy of beta-blockade with regards to heart rate (HR) control and image quality in an unselected patient cohort. METHODS: We studied 150 consecutive patients (104 men/46 female; mean age, 56+/-13 years) referred for coronary CTA. Intravenous metoprolol (5-20mg) was administered to patients with a HR >65 beats per minute (bpm). The goal HR was defined as an average HR <65 bpm without a single measurement above 68 bpm. RESULTS: Overall, 45% (68/150) of patients met the HR criteria for beta-blocker administration of which 76% (52/68) received metoprolol (mean dose 12+/-10mg). Of the 52 patients who received beta-blocker versus the 98 who did not, 18 (35%) versus 62 (64%) patients achieved the goal HR, respectively. All patients who achieved the target HR had an evaluable CTA while five patients who did not achieve the target HR had at least one non-evaluable coronary artery due to motion artifact. There was also a significant reduction in any motion artifact among those who achieved the goal HR as compared to those who did not (p=0.001). Logistic regression revealed an increase in the odds of stair step artifact of 11.6% (95% CI: 2.4% decrease, 27.5% increase) per 1 bpm increase in the standard deviation of scan HR. CONCLUSION: Overall, efficacy of beta-blocker administration to reach target HR is limited. Improvements in CT scanner temporal resolution are mandatory to achieve consistently high image quality independent of HR and beta-blocker administration.     

Optimal image reconstruction intervals for non-invasive coronary angiography with 64-slice CT

The reconstruction intervals providing best image quality for non-invasive coronary angiography with 64-slice computed tomography (CT) were evaluated. Contrast-enhanced, retrospectively electrocardiography (ECG)-gated 64-slice CT coronary angiography was performed in 80 patients (47 male, 33 female; mean age 62.1±10.6 years). Thirteen data sets were reconstructed in 5% increments from 20 to 80% of the R-R interval. Depending on the average heart rate during scanning, patients were grouped as <65 bpm (n=49) and ≥65 bpm (n=31). Two blinded and independent readers assessed the image quality of each coronary segment with a diameter ≥1.5 mm using the following scores: 1, no motion artifacts; 2, minor artifacts; 3, moderate artifacts; 4, severe artifacts; and 5, not evaluative. The average heart rate was 63.3±13.1 bpm (range 38–102). Acceptable image quality (scores 1–3) was achieved in 99.1% of all coronary segments (1,162/1,172; mean image quality score 1.55±0.77) in the best reconstruction interval. Best image quality was found at 60% and 65% of the R-R interval for all patients and for each heart rate subgroup, whereas motion artifacts occurred significantly more often (P<0.01) at other reconstruction intervals. At heart rates <65 bpm, acceptable image quality was found in all coronary segments at 60%. At heart rates ≥65 bpm, the whole coronary artery tree could be visualized with acceptable image quality in 87% (27/31) of the patients at 60%, while ten segments in four patients were rated as non-diagnostic (scores 4–5) at any reconstruction interval. In conclusion, 64-slice CT coronary angiography provides best overall image quality in mid-diastole. At heart rates <65 bpm, diagnostic image quality of all coronary segments can be obtained at a single reconstruction interval of 60%.     

Optimal ECG Trigger Point in Electron-Beam CT Studies: Three Methods for Minimizing Motion Artifacts

RATIONALE AND OBJECTIVES: The authors hypothesized that electrocardiographic triggering near end systole could minimize motion artifacts in electron-beam computed tomography (CT) of the coronary artery. MATERIALS AND METHODS: The study included 2,660 patients who underwent coronary artery calcium scanning with electron-beam CT. Trigger times were as follows: end of T wave, 120 to 25 msec before end of T wave, 25-50 msec after end of T wave, 40%, 45%, 50%, 55%, 60%, 70%, 75%, 80%, 90%, and 100% of R-R interval. The authors divided each group into seven subgroups according to heart rate. The percentages of cases with motion artifact in the right coronary artery were computed. Optimal trigger times were defined for each group, as well as for scan acquisitions of 250 and 200 msec. RESULTS: The optimal trigger times were as follows for heart rates of less than 50, 51-60, 61-70, 71-80, 81-90, 91-100, and more than 100 beats per minute, respectively: for 100-msec scans, 359 (27% of the R-R interval), 228 (31%), 314 (34%), 304 (38%), 289 (41%), 283 (45%), and 274 msec (48%) after the R wave; for 250-msec scans, 840 (63%), 654 (60%), 240 (26%), 224 (28%), 219 (31%), 208 (33%), and 200 msec (35%) after the R wave; and for 200-msec scans, 722 (65%), 687 (63%), 249 (27%), 248 (31%), 244 (35%), 233 (37%), and 223 msec (39%) after the R wave. CONCLUSION: The use of these new electrocardiographic triggers before end systole yielded the lowest percentage of motion artifacts (<3% across all heart rates), much lower than for conventional triggers (51% of cases with motion artifact for 80% trigger, P < .001).     

Single-detector helical CT in PET-CT: assessment of image quality

OBJECTIVE: CT in positron emission tomography (PET)-CT imaging is often performed as a single scan from the base of the skull to the groin, potentially resulting in degradation of the quality of CT scans depending on the position of the patient's arms and mode of breathing and the use and timing of IV contrast injection. The aim of our study was to assess the impact of artifacts on the diagnostic quality of CT scans using a single-detector helical CT scanner in PET-CT imaging. MATERIALS AND METHODS: Two radiologists retrospectively evaluated the diagnostic image quality of CT scans obtained with PET-CT in 81 patients with lymphoma. The severity of the artifacts related to the position of the patient's arms beside the body, the influence of breathing motion, and the presence of contrast material in the upper thoracic veins were ranked using a 4-point scale. RESULTS: Performing CT with the patient's arms positioned beside the body resulted in streak artifacts, predominantly in the upper abdomen, that were graded as mild in 22%, moderate in 40%, and severe in 38% of the scans. A patient's weight significantly correlated with the degree of severity of the artifacts (p < 0.05). Shallow breathing by the patient during scanning caused blurring and double-imaging, again predominantly in the upper abdomen, that were graded as mild in 23%, moderate in 49%, or severe in 28% of the scans. In 84% of the CT scans obtained with IV contrast material, the image quality of the upper thoracic region was moderately (27%) or severely (57%) degraded by streak artifacts from highly concentrated contrast material in the upper thoracic veins. CONCLUSION: The use of a single-detector CT scanner in whole-body PET-CT decreases the image quality of CT scans because of streak artifacts that occur predominantly in scans of the upper abdomen. Scanning with the patient's arms raised eliminates the streak artifacts in scans of the abdominal region. With the new generation of PET-CT devices equipped with MDCT scanners, breathing motion artifacts can be expected to be eliminated if protocols for breath-hold CT are applied. Reversing the direction of CT scanning allows one to avoid imaging the thoracic region at a time when undiluted IV contrast material is still present in the upper thoracic veins.     

Comparison of artifacts on coronal reformation and axial CT pulmonary angiography images using single-detector and 4- and 8-detector multidetector-row helical CT scanners

RATIONALE AND OBJECTIVES: The aim of this study is to compare the degree of stair-step artifact on coronal reformation computed tomographic (CT) pulmonary angiography images obtained using single-detector helical CT (SDCT), four-detector (4-MDCT), and eight-detector multidetector-row CT (8-MDCT) and compare the degree of motion artifact on the corresponding axial CT images. MATERIALS AND METHODS: Three groups of consecutive patients imaged by means of CT angiography for suspected pulmonary embolus were retrospectively identified by using CT records at our institution: (1) group A (n = 38), SDCT; (2) group B (n = 36), 4-MDCT; and (3) group C (n = 74), 8-MDCT. For each case, coronal multiplanar volume reformation maximal intensity projection images were created by using a standard technique. All images were reviewed in a randomized fashion by two thoracic radiologists who were blinded to the type of CT scanner. Stair-step artifact of pulmonary arteries on coronal reformation images was graded by consensus agreement using a four-point scale (0 = no artifact to 3 = severe artifact). Axial images were assessed for six parameters of motion artifact. The sum of these grades resulted in a total motion score, with a potential range of 0 (no motion) to 12 (severe motion). Statistical analysis was performed using the Mann-Whitney test. RESULTS: Stair-step artifacts were significantly higher for SDCT (mean, 2.9; median, 3) compared with 4-MDCT (mean, 2.2; median, 2; P < .0001) and 8-MDCT (mean, 1.5; median, 1; P < .0001). Total motion scores were significantly higher for SDCT (mean, 9.3) compared with 4-MDCT (mean, 8.4; P = .03) and 8-MDCT (mean, 6.8; P < .0001). CONCLUSION: Stair-step artifacts are significantly higher with SDCT compared with MDCT. For MDCT, eight-detector scanners produce images with significantly less artifact than four-detector scanners.     

Image quality, motion artifacts, and reconstruction timing of 64-slice coronary computed tomography angiography with 0.33-second rotation speed

OBJECTIVES: We sought to evaluate the impact of patients' heart rate (HR) on coronary CTA image quality (IQ) and motion artifacts using a 64-slice scanner with 0.33/360 degrees rotation. MATERIALS AND METHODS: Coronary CTA data sets of 32 patients (HR 65 bpm to 75 bpm, n = 7) examined on a 64-slice scanner (Sensation 64, Siemens Medical Solutions, Forchheim, Germany) with 0.33s/360 degrees gantry rotation speed were analyzed. All patients had suspicion of coronary artery disease. Data acquisition was performed using 64 x 0.6-mm collimation, and contrast enhancement was provided by injection of 80 mL of iopromide (5 mL/s + NaCl). Images were reconstructed throughout the RR interval using half-scan and dual-segment reconstruction. IQ was rated by 2 observers using a 3-point scale from excellent (1) to nondiagnostic (3) for coronary segments. Quality was correlated to the HR, time point of optimal IQ analyzed, and the benefit of dual-segment reconstruction evaluated. RESULTS: Overall mean IQ was 1.31 +/- 0.32 for all HR, with IQ being 1.08 +/- 0.12 for HR 65 bpm 75 bpm (P = 0.0003). Dual-segment reconstruction did not significantly improve IQ in any HR group (P = NS). Mean IQ was significantly better for LAD than for RCA (P < 0.0001) and LCX (P < 0.01). A total of 3.5% (11/318) of coronary artery segments were rated nondiagnostic by at least one reader based on motion artifacts. Although in HR < 65 bpm, the best IQ was predominately in diastole (93%), in HR > 75 bpm, the best IQ shifted to systole in most cases (86%). CONCLUSIONS: Temporal resolution at 0.33-second rotation allows for diagnostic IQ within a wide range of HR using half-scan reconstruction. With increasing HR the time point of best IQ shifts from mid-diastole to systole.     

Frequency of common bile duct motion artifacts caused by inferior vena cava pulsation on magnetic resonance cholangiopancreatography.

PURPOSE: We assessed the frequency of common bile duct (CBD) motion artifacts caused by inferior vena cava (IVC) pulsation on magnetic resonance cholangiopancreatography (MRCP). METHODS: We retrospectively evaluated CBD motion artifacts in 4 MRCP sequences from each of 115 consecutive patients. RESULTS: We observed 37 (32.2%) ghost artifacts at the ventral and dorsal aspects of the CBD on transaxial, half-Fourier acquisition single-shot turbo spin-echo (HASTE-ax) images; no such artifacts were observed on transaxial T(2)-weighted turbo spin-echo images. In 10 patients, we observed 9 (7.8%) pseudo-defects of the CBD on 3-dimensional T(2)-weighted turbo spin-echo with navigator-triggered prospective acquisition correction technique MRCP and 6 (5.2%) pseudo-defects on single-shot rapid acquisition with relaxation enhancement MRCP. Pseudo-defects were significantly more frequent in patients with ghost artifacts than without (9 of 37 [24.3%] versus one of 78 [1.3%]; P<0.01, McNemar test). CONCLUSION: Although uncommon, pseudo-defects of the CBD caused by IVC pulsation are observed on MRCP. MRCP interpretation that includes comparison with HASTE-ax images can diminish the potential misinterpretation of such CBD motion artifact as bile duct tumor or biliary stone.     

Effect of artifacts due to flowing blood on the reproducibility of phase-contrast measurements of myocardial motion

The reproducibility of myocardial motion trajectories calculated from cine phase-contrast (PC) velocity data is reduced by artifacts due to the inconsistent motion of intracardiac blood. Spatial presaturation reduces these artifacts but requires a longer sequence TR, with a potentially negative effect on trajectory accuracy and reproducibility. We investigated the effect of spatial presaturation on trajectory reproducibility. A midventricular transaxial slice was imaged in five normal volunteers. The same slice was imaged three times each with sequences using spatial presaturation or not. Because the most serious artifacts originate in the heart chambers and propagate in the phase-encoded direction, myocardial regions that were in line with the heart chambers (in the phase-encode direction) had the highest artifact level in the scans without spatial presaturation. The reproducibility of trajectories for regions placed in these areas (the anterior wall, septum and posterior wall in the transaxial scans with phase encoding in the anterior-posterior direction) improved by a factor of two when presaturation was used (P < .001). In areas that were not in line with the heart chambers (eg, the anterior aspect of the lateral wall in the transaxial scans), the effect of presaturation was not significant. These results correlate well with the measured reduction in artifact level. The reproducibility of myocardial motion trajectories over large areas of the heart is improved to approximately 1 mm when presaturation is used. Therefore, use of presaturation is recommended for myocardial motion studies using cine PC velocity data.     

Study on motion artifacts in coronary arteries with an anthropomorphic moving heart phantom on an ECG-gated multidetector computed tomography unit

Acquisition time plays a key role in the quality of cardiac multidetector computed tomography (MDCT) and is directly related to the rotation time of the scanner. The purpose of this study is to examine the influence of heart rate and a multisector reconstruction algorithm on the image quality of coronary arteries of an anthropomorphic adjustable moving heart phantom on an ECG-gated MDCT unit. The heart phantom and a coronary artery phantom were used on a MDCT unit with a rotation time of 500 ms. The movement of the heart was determined by analysis of the images taken at different phases. The results indicate that the movement of the coronary arteries on the heart phantom is comparable to that in a clinical setting. The influence of the heart rate on image quality and artifacts was determined by analysis of several heart rates between 40 and 80 bpm where the movement of the heart was synchronized using a retrospective ECG-gated acquisition protocol. The resulting reformatted volume rendering images of the moving heart and the coronary arteries were qualitatively compared as a result of the heart rate. The evaluation was performed on three independent series by two independent radiologists for the image quality of the coronary arteries and the presence of artifacts. The evaluation shows that at heart rates above 50 bpm the influence of motion artifacts in the coronary arteries becomes apparent. In addition the influence of a dedicated multisector reconstruction technique on image quality was determined. The results show that the image quality of the coronary arteries is not only related to the heart rate and that the influence of the multisector reconstruction technique becomes significant above 70 bpm. Therefore, this study proves that from the actual acquisition time per heart cycle one cannot determine an actual acquisition time, but only a mathematical acquisition time.     

Patient-specific contrast injection protocols for cardiovascular multidetector row computed tomography

OBJECTIVE: To develop patient-specific contrast injections for uniform enhancement of cardiovascular multidetector row computed tomography (MDCT) images. METHODS: Sixty-two patients were imaged using electrocardiogram (ECG)-gated spiral MDCT. Thirty patients (group 1) received a uniphasic injection; the remaining 32 patients (group 2) received patient-specific multiphasic injections. For group 2 patients, the vasculature between injection and imaging sites was considered a "gray box" whose transfer function was determined from a test bolus injection and the resulting enhancement in the left side of the heart. This transfer function was used to determine the injection necessary to achieve 250 Hounsfield units in the left side of the heart. Intraindividual and interindividual variation of enhancement were determined for both groups. Superior vena cava (SVC) artifacts were graded on a 4-point scale. RESULTS: The measured indices of intraindividual variation were significantly smaller in group 2 than in group 1 (P < 0.05), indicating improved uniformity with patient-specific injections. The interindividual variation of mean enhancement in group 2 was smaller than in group 1, but the difference was not significant. The severity of SVC artifacts was significantly reduced (P < 0.05) for thinner patients (<83 kg) in group 2 compared with similar patients in group 1. CONCLUSIONS: Patient-specific multiphasic contrast injections yielded more uniform enhancement in the left side of the heart on MDCT images with reduced intraindividual variation of enhancement compared with standard uniphasic injections. Patient-specific injections also reduced SVC artifacts in patients <83 kg.     

Thin-section CT of the lung: influence of 0.5-s gantry rotation and ECG triggering on image quality

The aim of this study was to determine if ECG triggering and a shorter acquisition time of 0.5-s rotation decrease cardiac motion artifacts of thin-section CT of the lung. In 25 patients referred for thin-section thoracic CT, 1-mm thin-section slices were performed with a scanning time of 0.5 s with ECG gating, 0.5 s and 1 s during the diastolic phase of the heart at five identical anatomical levels from the aortic arch to lung basis. At each anatomical level and for each lung, cardiac motion artifacts were graded independently on a four-point scale by three readers. Patients were divided into two groups according to their heart rate. A four-way analysis of variance was used to assess differences between the three modalities. Mean cardiac motion artifacts scores were rated 1.23+/-0.02, 1.47+/-0.02, and 1.79+/-0.02, at 0.5 s with ECG gating, 0.5 s without ECG gating, and 1 s, respectively (F=139, p<0.0001). At the four anatomical levels below the aortic arch, the left lung scores were greater than the right lung score for the three modalities. For the modality 0.5 s with ECG gating no difference of scores was found between patients grouped according to their cardiac frequency. The 0.5-s gantry rotation with or without ECG gating scans reduces cardiac motion artifacts on pulmonary thin-section CT images and is mainly beneficial for the lower part of the left lung.     

When, why, and how to examine the heart during thoracic CT: Part 1, basic principles

OBJECTIVE: MDCT systems with fast scanning capabilities can acquire images of the thorax with reduced cardiac motion artifacts, enabling improved evaluation of the heart and surrounding structures in the course of routine thoracic CT. This article describes the principles of including an evaluation of the heart in the course of a chest CT examination in terms of both examination technique and image interpretation. In addition, both the normal appearances and some of the most common abnormal appearances of the cardiac structures will be described. CONCLUSION: Details concerning the cardiac structures can inform interpretation of thoracic CT studies and can influence the patient's clinical management. Both unenhanced and contrast-enhanced scans can detect significant cardiac disorders that may otherwise go undetected. In certain situations, a CT examination of the entire chest, complemented by cardiac gating, can provide a more dedicated analysis of the heart and coronary arteries, providing both morphologic and functional information.