Borut Marincek

Low-Dose CT Coronary Angiography in the Step-and-Shoot Mode: Diagnostic Performance

Objective: To investigate the performance of low-dose, dual-source computed tomography (DSCT) coronary angiography in the step-and-shoot (SAS) mode for the diagnosis of significant coronary artery stenoses in comparison with conventional coronary angiography (CCA). Design, setting and patients: Prospective, single-centre study conducted in a referral centre enrolling 120 patients (71 men, mean (SD) age 68 (9) years, mean (SD) body mass index 26.2 (3.2) kg/m2). All study participants underwent DSCT in the SAS mode and CCA within 14 days. Twenty-seven patients were given intravenous β blockers for heart rate reduction before CT. Patients were excluded if a target heart rate ⩽70 bpm could not be achieved by β blockers or when the patients were in non-sinus rhythm. Two blinded readers independently evaluated coronary artery segments for assessability and for the presence of significant (>50%) stenoses. Sensitivity, specificity, negative (NPV) and positive predictive values (PPV) were determined, with CCA being the standard of reference. Radiation dose values were calculated. Results: DSCT coronary angiography in the SAS mode was successfully performed in all 120 patients. Mean (SD) heart rate during scanning was 59 (6) bpm (range 44–69). 1773/1803 coronary segments (98%) were depicted with a diagnostic image quality in 109/120 patients (91%). The overall patient-based sensitivity, specificity, PPV and NPV for the diagnosis of significant stenoses were 100%, 93%, 94% and 100%, respectively. The mean (SD) effective dose of the CT protocol was 2.5 (0.8) mSv (range 1.2–4.4). Conclusions: DSCT coronary angiography in the SAS mode allows, in selected patients with a regular heart rate, the accurate diagnosis of significant coronary stenoses at a low radiation dose.

Dual-source CT in step-and-shoot mode: noninvasive coronary angiography with low radiation dose.

PURPOSE To prospectively investigate computed tomographic (CT) image quality parameters by using different protocols and to calculate radiation dose estimates for noninvasive coronary angiography performed with dual-source CT in the step-and-shoot (SAS) mode. MATERIALS AND METHODS This study was local ethics board approved; written informed consent was obtained from all patients. In the preliminary portion of the study, 40 patients underwent CT coronary angiography in the SAS mode: at 100 kV (protocol A) in 22 patients with a body mass index (BMI) of less than 25 kg/m(2) and at 120 kV (protocol B) in 18 patients with a BMI of 25-30 kg/m(2). Both protocols involved use of an attenuation-based tube current and 1 mL of contrast material per kilogram of body weight. The final portion of the study involved 50 additional patients: 21 patients with a BMI of 25-30 kg/cm(2) assigned to protocol B and 29 patients with a BMI of less than 25 kg/cm(2) assigned to protocol C, which was performed with 100 kV, an attenuation-based tube current, and a reduced contrast material dose of 0.8 mL/kg. Image quality was independently assessed. Attenuation in the aorta and coronary arteries and image noise were measured. Radiation dose was estimated. RESULTS Mean image noise was similar with protocols A and B. Mean attenuation in the aorta and coronary arteries with protocol A (444 HU) was significantly (P < .001) higher than that with protocol B (358 HU). The reduced contrast material dose in protocol C yielded attenuation similar to that with protocol B. Diagnostic image quality was achieved with all protocols in 1237 (97.9%) of 1264 coronary segments. No significant differences in image quality between the 100- and 120-kV protocols were found. Mean heart rate had a significant effect on motion artifacts (area under receiver operating characteristic curve [AUC] = 0.818; 95% confidence interval [CI]: 0.723, 0.892; P < .001), whereas heart rate variability had a significant effect on stair-step artifacts (AUC = 0.79; 95% CI: 0.687, 0.865; P < .001). The mean estimated effective dose was 1.2 mSv +/- 0.2 for protocols A and C and 2.6 mSv +/- 0.5 for protocol B. CONCLUSION Dual-source SAS-mode CT coronary angiography yielded diagnostic image quality for 97.9% of coronary segments at a low radiation dose.

Dual-Source CT Coronary Angiography: Image Quality, Mean Heart Rate, and Heart Rate Variability

OBJECTIVE The purpose of this study was to evaluate the effect of mean heart rate and heart rate variability on the image quality of dual-source CT coronary angiography. SUBJECTS AND METHODS Eighty patients underwent dual-source CT coronary angiography. Thirteen data sets were reconstructed in 5% steps from 20-80% of the R-R interval. Heart rate variability was calculated as SD of mean heart rate. Two independent blinded reviewers assessed the image quality of each segment. RESULTS Mean heart rate was 65.3 +/- 13.9 (SD) beats per minute (bpm) (range, 35-99 bpm) with a variability of 3.4 +/- 4.1 bpm (range, 0.4-17.5 bpm). Image quality was sufficient for diagnosis for 97.8% (1,043/1,066) of arterial segments. No significant correlation was found between mean heart rate and image quality in any segment or any coronary artery. No significant correlation was found between heart rate variability and image quality in any segment, the right coronary artery, or the left anterior descending artery, but there was a significant (p < 0.05) correlation in the left circumflex artery. A significant correlation (p < 0.05) between overall image quality was found for mean and variability of heart rate as shared predictors, the latter having a greater contribution. CONCLUSION The overall image quality of dual-source CT coronary angiography is sufficient for diagnosis within a wide range of mean heart rates and variability of heart rates. Only heart rates that are both high and variable significantly deteriorate image quality, but the quality remains adequate for diagnosis.

Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dual-source CT.

PURPOSE To assess the diagnostic performance of dual-energy dual-source computed tomography (CT) in the detection of endoleaks after endovascular abdominal aortic aneurysm (AAA) repair. MATERIALS AND METHODS This study was local ethics board approved, and written informed consent was obtained from all patients. One hundred eighteen patients (21 women, 97 men; mean age, 74 years +/- 8 [standard deviation]) underwent follow-up dual-energy dual-source CT during the nonenhanced, arterial, and delayed phases after AAA repair. Delayed phase CT images were acquired in the dual-energy mode for reconstruction of virtual nonenhanced images. Two blinded and independent readers evaluated the data for the presence or absence of endoleaks during three reading sessions: Standard nonenhanced, arterial phase, and delayed phase images were read during session A; virtual nonenhanced, arterial phase, and delayed phase images, during session B; and virtual nonenhanced and delayed phase images, during session C. Sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) were calculated, with the session A image data set as the reference standard. Radiation dose parameters were estimated. RESULTS Reading session A revealed that 52 (44%) of 118 patients had endoleaks. Overall sensitivity, specificity, NPV, and PPV for CT endoleak detection during sessions B and C were identical: 100%, 97%, 100%, and 96%, respectively. The accuracy of the session B and session C readings was not significantly different from that of the session A reading (P = .50). The effective radiation dose in the image acquisition protocol involving one dual-energy scan was significantly (P < .001) lower than the effective doses in the protocols involving standard triple-phase scanning (mean difference, 61%) and standard nonenhanced and delayed phase scanning (mean difference, 41%). CONCLUSION Compared with standard protocols, one dual-energy dual-source CT scan performed during the delayed phase with reconstruction of virtual nonenhanced images enables detection of endoleaks after endovascular AAA repair with high accuracy and a considerably lower radiation dose.

Image quality and reconstruction intervals of dual-source CT coronary angiography: recommendations for ECG-pulsing windowing.

Purpose:To evaluate reconstruction intervals and image quality in dual-source computed tomography (DSCT) coronary angiography for optimal placement of the ECG-pulsing window. Materials and Methods:DSCT coronary angiography was performed in 60 patients. Thirteen datasets were reconstructed in 5% increments from 20–80%. Two readers independently assessed image quality of each segment in each percentage-interval, using scores ranging from 1 (no motion artifacts) to 4 (nonevaluable). Results:Mean heart rate (HR) was 69.0 ± 18.9 beats per minute (bpm) (range, 35–117 bpm). Diagnostic image quality (scores 1–3) was found in 97.8% of all segments (763 of 780). The 70% RR-interval provided best image quality in all patients and all HRs. The narrowest reconstruction window providing diagnostic image quality was 60–70% for HR <60 bpm, 60–80% for 60–70 bpm, 55–80% for 70–80 bpm, and 30–80% for HR >80 bpm. Conclusions:DSCT coronary angiography provides best image quality for various HRs at 70%. The ECG-pulsing window can be adapted according to the HR while maintaining diagnostic image quality.

Dual-source computed tomography coronary angiography: influence of obesity, calcium load, and heart rate on diagnostic accuracy

AIMS To prospectively investigate the diagnostic accuracy of dual-source computed tomography coronary angiography (CTCA) to diagnose coronary stenoses in relation to body mass index (BMI), Agatston score (AS), and heart rate (HR) as compared with catheter coronary angiography (CCA). METHODS AND RESULTS Hundred and fifty consecutive patients (47 female, mean age 62.9 +/- 12.1 years) underwent dual-source CTCA without HR control. Patients were divided into subgroups depending on the median of their BMI (26.0 kg/m2), AS (194), and HR (66 b.p.m.). CCA was considered the standard of reference. Mean BMI was 26.5 +/- 4.2 kg/m2 (range 18.3-39.1 kg/m2), mean AS was 309 +/- 408 (range 0-4387), and HR was 68.5 +/- 12.6 b.p.m. (range 35-102 b.p.m.). Diagnostic image quality was found in 98.1% of all segments (2020/2059). Considering not-evaluative segments at CTCA as false-positive, overall per-patient sensitivity, specificity, positive, and negative predictive value were 96.6%, 86.8%, 82.6%, and 97.5%, respectively. High HR did not deteriorate diagnostic accuracy of CTCA. High BMI and AS were associated with a decrease in per-patient specificity to 84.1% and 77.8%, respectively, while sensitivity and negative predictive value remained high. CONCLUSION Dual-source CTCA provides high diagnostic accuracy irrespective of the HR and serves as a modality to rule-out coronary artery stenoses even in patients with high BMI and AS.

Low-dose, 128-slice, dual-source CT coronary angiography: accuracy and radiation dose of the high-pitch and the step-and-shoot mode

Objective To compare the diagnostic accuracy and radiation doses of two low-dose protocols for coronary artery imaging with second-generation, dual-source CT in comparison with catheter angiography (CA). Design, setting and patients Prospective, single-centre study conducted in a referral centre enrolling 100 patients with low-to-intermediate risk and suspicion of coronary artery disease. All patients underwent contrast-enhanced, 128-slice, dual-source CT coronary angiography and CA. Patients were randomly assigned to two different low-dose CT protocols (each 100 kV/320 mA): in group A (n=50), CT was performed using the prospectively electrocardiography (ECG)-gated step-and-shoot (SAS) mode; in group B (n=50), CT was performed using the prospectively ECG-gated high-pitch mode (pitch 3.4). The image quality and presence or absence of significant coronary stenosis in all coronary segments were evaluated by two blinded and independent observers. CA served as the standard of reference. Results Sixty-one significant stenoses were found in group A, and 69 in group B. There was no significant difference in age (group A, 62±8yrs; group B, 63±8yrs; p=0.72), body mass index (group A, 26.4±3.1kg/m2; group B, 25.9±2.8kg/m2; p=0.41) and heart rate (HR) (group A, 58±8bpm; group B, 56±10bpm; p=0.66) between the groups. Diagnostic image quality was obtained in 98.6% (651/660) of segments in group A and in 98.9% (642/649) in group B, with no significant differences between groups. Sensitivity, specificity and positive and negative predictive values were 94%, 91%, 85% and 97% per-patient in group A, and 93%, 94%, 89% and 97% per-patient in group B (no significant differences). The effective radiation dose in group B (0.9±0.1 mSv) was significantly (p<0.01) lower than that in group A (1.4±0.4 mSv). Conclusions Both the high-pitch and the SAS mode for low-dose CT coronary angiography provide high accuracy for the assessment of significant coronary stenoses, while the high-pitch mode further significantly lowers the radiation dose.

Radiation dose of cardiac dual-source CT: The effect of tailoring the protocol to patient-specific parameters

OBJECTIVE To determine the radiation doses and image quality of different dual-source computed tomography coronary angiography (CTCA) protocols tailored to the heart rate (HR) and body mass index (BMI) of the patients. MATERIALS AND METHODS Two hundred consecutive patients (68 women; mean age 61+/-9 years) underwent either helical CTCA with retrospective ECG-gating or sequential CT with prospective ECG-triggering: 50 patients (any BMI, any HR) were examined with a standard, non-tailored protocol (helical CTCA, 120 kV, 330 mAs), whereas the other 150 patients were examined with a tailored protocol: 40 patients (group A, BMI<or=25 kg/sqm, HR<or=70 bpm) with sequential CTCA (100 kV, 190 mAs(ref)), 43 patients (group B, BMI</=25 kg/sqm, HR>70 bpm) with helical CTCA (100 kV, 220 mAs), 28 patients (group C, BMI>25 kg/sqm, HR<or=70 bpm) with sequential CTCA (120 kV, 330 mAs(ref)), and 39 patients (group D, BMI>25 kg/sqm, HR>70 bpm) with helical CTCA (120 kV, 330 mAs). The effective radiation dose estimates were calculated from the dose-length-product for each patient. Image quality was classified as being diagnostic or non-diagnostic in each coronary segment. RESULTS Image quality was diagnostic in 2403/2460 (98%) and non-diagnostic in 57/2460 (2%) of all coronary segments. No significant differences in image quality were found among all five CTCA protocols (p=0.78). The non-tailored helical CTCA protocol was associated with a radiation dose of 9.0+/-1.0 mSv, being significantly higher compared to that using sequential CTCA (group A: 1.3+/-0.3 mSv, p<0.001; group C: 2.9+/-0.6 mSv, p<0.001), and helical CTCA at reduced tube voltage and tube current (group B: 4.2+/-0.6 mSv, p<0.01). No significant differences were found compared to the non-tailored CTCA protocol in patients with HR>70 bpm (group D: 8.5+/-0.9 mSv, p=0.51). CONCLUSIONS Dual-source CTCA is associated with radiation doses ranging between 1.3 and 9.0 mSv, depending on the protocol used. Tailoring of the CTCA protocol to the HR and BMI of the individual patient results in dose reductions of up to 86%, while maintaining a diagnostic image quality of the examination.

Dual-energy contrast-enhanced computed tomography for the detection of urinary stone disease

Objectives:To assess the value of dual-energy contrast-enhanced computed tomography (CT) imaging for the detection of urinary stone disease using dual-source CT. Materials and Methods:Forty consecutive patients (mean age 46.6 ± 16.2 years, range 27–85 years) suspected of having urinary stone disease underwent dual-source CT of the urinary tract. A 3-phasic CT scan protocol consisting of a standard unenhanced scan, a nephrographic, and an excretory phase of contrast enhancement was performed. The nephrographic phase scan was acquired in the dual-energy mode (80 kV/400 mA and 140 kV/95 mA) allowing reconstruction of virtual unenhanced images. Two blinded readers independently compared standard and virtual unenhanced CT for the number, size, and location of urinary stones. Measurements of anteroposterior abdominal diameters were performed to determine abdominal obesity. Results:Standard unenhanced CT revealed 35 uroliths in 18 of the 40 patients (18 of 40; 45%), virtual unenhanced CT demonstrated 26 uroliths in 15 of the 40 patients (15 of 40; 38%) ([kappa] value 0.89). Three false-negative and no false-positive ratings occurred using virtual unenhanced CT, and false-negative ratings solely occurred in obese patients. Sensitivity, specificity, positive predictive, and negative predictive values for virtual unenhanced CT for the diagnosis of urinary stone disease were 83%, 100%, 100%, and 88%, respectively. Conclusions:Virtual unenhanced CT images reconstructed from contrast-enhanced dual-energy CT allow detection of urinary stones with good sensitivity and excellent specificity, but sensitivity is decreased in abdominal obese patients.

How Does MRI Work? An Introduction to the Physics and Function of Magnetic Resonance Imaging

Spins and the Nuclear Magnetic Resonance Phenomenon * Relaxation * Image Contrast * Slice Selection and Spatial Encoding * Factors affecting the Signal-to-Noise Ratio * The MR Scanner * Basic Pulse Sequences * Fast Pulse-Sequences * Fat Suppression Techniques * Parallel Imaging * Cardiovascular Imaging * MR Contrast Agents * MR Artifacts * High-Field Cflinical MR Imaging * Bioeffects and Safety * Glossary * Subject Index.