Thomas Henzler

Evaluation of Heavily Calcified Vessels with Coronary CT Angiography: Comparison of Iterative and Filtered Back Projection Image Reconstruction

PURPOSE To prospectively compare traditional filtered back projection (FBP) and iterative image reconstruction for the evaluation of heavily calcified arteries with coronary computed tomography (CT) angiography. MATERIALS AND METHODS The study had institutional review board approval and was HIPAA compliant. Written informed consent was obtained from all patients. Fifty-five consecutive patients (35 men, 20 women; mean age, 58 years ± 12 [standard deviation]) with Agatston scores of at least 400 underwent coronary CT angiography and cardiac catheterization. Image data were reconstructed with both FBP and iterative reconstruction techniques with corresponding cardiac algorithms. Image noise and subjective image quality were compared. To objectively assess the effect of FBP and iterative reconstruction on blooming artifacts, volumes of circumscribed calcifications were measured with dedicated volume analysis software. FBP and iterative reconstruction series were independently evaluated for coronary artery stenosis greater than 50%, and their diagnostic accuracy was compared, with cardiac catheterization as the reference standard. Statistical analyses included paired t tests, Kruskal-Wallis analysis of variance, and a modified McNemar test. RESULTS Image noise measured significantly lower (P = .011-.035) with iterative reconstruction instead of FBP. Image quality was rated significantly higher (P = .031 and .042) with iterative reconstruction series than with FBP. Calcification volumes measured significantly lower (P = .019 and .026) with iterative reconstruction (44.3 mm(3) ± 64.7 and 46.2 mm(3) ± 68.8) than with FBP (54.5 mm(3) ± 69.5 and 56.3 mm(3) ± 72.5). Iterative reconstruction significantly improved some measures of per-segment diagnostic accuracy of coronary CT angiography for the detection of significant stenosis compared with FBP (accuracy: 95.9% vs 91.8%, P = .0001; specificity: 95.8% vs 91.2%, P = .0001; positive predictive value: 76.9% vs 61.1%, P = .0001). CONCLUSION Iterative reconstruction reduces image noise and blooming artifacts from calcifications, leading to improved diagnostic accuracy of coronary CT angiography in patients with heavily calcified coronary arteries.

Closing in on the K Edge: Coronary CT Angiography at 100, 80, and 70 kV—Initial Comparison of a Second- versus a Third-Generation Dual-Source CT System

PURPOSE To prospectively evaluate radiation and contrast medium requirements for performing high-pitch coronary computed tomographic (CT) angiography at 70 kV using a third-generation dual-source CT system in comparison to a second-generation dual-source CT system. MATERIALS AND METHODS All patients gave informed consent for this institutional review board-approved study. Forty-five patients (median age, 52 years; 27 men) were imaged in high-pitch mode with a third-generation dual-source CT system at 70 kV (n = 15) or with a second-generation dual-source CT system at 80 or 100 kV (n = 15 for each). Tube voltage was based on body mass index: 80 or 70 kV for less than 26 kg/m(2) versus 100 kV for 26-30 kg/m(2). For the 80- and 100-kV protocols, 80 mL of contrast material was injected, versus 45 mL for the 70-kV protocol. Data were reconstructed by using a second-generation iterative reconstruction algorithm for second-generation dual-source CT and a recently introduced third-generation iterative reconstruction algorithm for third-generation dual-source CT. Objective image quality was measured for various regions of interest, and subjective image quality was evaluated with a five-point Likert scale. RESULTS The signal-to-noise ratio of the coronary CT angiography studies acquired with 70 kV was significantly higher (70 kV: 14.3-17.6 vs 80 kV: 7.1-12.9 vs 100 kV: 9.8-12.9; P < .0497) than those acquired with the other two protocols for all coronary arteries. Qualitative image quality analyses revealed no significant differences between the three CT angiography protocols (median score, 5; P > .05). The mean effective dose was 75% and 108% higher (0.92 mSv ± 0.3 [standard deviation] and 0.78 mSv ± 0.2 vs 0.44 mSv ± 0.1; P < .0001), respectively, for the 80- and 100-kV CT angiography protocols than for the 70-kV CT angiography protocol. CONCLUSION In nonobese patients, third-generation high-pitch coronary dual-source CT angiography at 70 kV results in robust image quality for studying the coronary arteries, at significantly reduced radiation dose (0.44 mSv) and contrast medium volume (45 mL), thus enabling substantial radiation dose and contrast medium savings as compared with second-generation dual-source CT.

Dual-Energy CT: Radiation Dose Aspects

OBJECTIVE Various applications for dual-energy CT (DECT) have been investigated and have shown substantial clinical benefits. However, only limited data are available regarding the radiation dose associated with DECT imaging. The purpose of this article is to review the available literature regarding the radiation dose associated with DECT imaging applications in comparison with conventional single-energy CT techniques. CONCLUSION The rediscovery of DECT and the increasing availability of this technique on clinical CT systems have opened new dimensions for CT. The advanced spectral differentiation of materials within the human body as well as the selective visualization or subtraction of iodinated contrast material or xenon provides both advanced visualization of disease-specific molecular substrates as well as additional functional information within a single scan.

Contrast-enhanced dual-energy CT of gastrointestinal stromal tumors: is iodine-related attenuation a potential indicator of tumor response?

Objectives:To assess the correlation of true nonenhanced (TNE) and virtually nonenhanced (VNE) images of abdominal dual-energy computed tomography (DECT) in patients with metastatic gastrointestinal stromal tumors (GIST), and further to investigate the correlation of iodine-related attenuation (IRA) of DECT with the Choi criteria. Material and Methods:Twenty-four consecutive patients (5 women aged 61 ± 10 years) with metastatic GIST underwent DECT of the abdomen (80 kV, 140 kV) using first-generation dual-source computed tomography (CT). All patients had at least one or more liver lesions (median, 4; maximum, 9). Image data were processed with a dedicated DECT software algorithm designed for evaluation of iodine distribution in soft tissue lesions, and VNE CT images were generated. The tumor density (according to Choi criteria) and the maximum transverse diameter of the lesions (according to Response Evaluation Criteria in Solid Tumors [RECIST]) were determined. TNE and VNE lesion attenuation and Choi criteria and IRA were correlated with each other. Results:A total of 291 liver lesions were evaluated, of which 220 were cystic and 71 were solid. The mean lesion size was 4.5 ± 3.2 cm (1.1–18.7 cm). The mean attenuation of all lesions was significantly higher in the TNE images than in the VNE images (P=0.0001). Pearson statistics revealed an excellent correlation of r=0.843 (P=0.0001) between IRA and Choi criteria for all lesions. DECT showed significantly higher IRA in progressive (23.3 ± 9.5 HU) lesions compared with stable or regressive (17.8 ± 9.1 HU) lesions (P=0.0185). Similarly, the Choi criteria differed significantly between progressive (39.9 ± 12.8 HU) and stable/regressive (31.1 ± 10.3 HU) lesions (P=0.0003). Conclusions:DECT is a promising imaging method for the assessment of treatment response in GIST, as IRA might be a more robust response parameter than the Choi criteria. VNE CT data calculated from DECT may eliminate the need for acquisition of a separate unenhanced data set.

Value of monoenergetic low-kV dual energy CT datasets for improved image quality of CT pulmonary angiography

PURPOSE High vessel attenuation and high contrast-to-noise ratio (CNR) are prerequisites for high diagnostic confidence in CT pulmonary angiography (CTPA). This study evaluated the impact of calculated monoenergetic dual-energy (DE) CTPA datasets on vessel attenuation and CNR. MATERIALS AND METHODS 50 Patients (24 men, mean age 68 ± 14 years) who underwent DE-CTPA were retrospectively included in this study. The 80 and 140-kV DE polyenergetic image data were used to calculate virtual monoenergetic image datasets in 10 kiloelectron volt (keV) increments from 40 to 120 keV. Vessel and soft tissue attenuation and image noise were measured in various regions of interest and the CNR was subsequently calculated. Differences in vessel attenuation and CNR were compared between the different monoenergetic datasets. The best monoenergetic dataset was then compared to the standard 120-kV polyenergetic dataset. RESULTS Vessel attenuation and CNR of 70-keV CTPA datasets were superior to all other monoenergetic image datasets (all p<0.05). 70-keV monoenergetic datasets provided a statistically significant 12% increase in mean vessel attenuation compared to standard 120-kV polyenergetic datasets (384 ± 117 HU vs. 342 ± 106 HU, respectively; p<0.0001) and a statistically significant 18% increase in mean CNR (29 ± 13 vs. 24 ± 11 respectively; p<0.0001). CONCLUSION Virtual 70-keV monoenergetic CTPA image datasets significantly increase vessel attenuation and CNR of DE-CTPA studies, suggesting that clinical application of low-keV monoenergetic reconstructions may allow a decrease in the amount of iodinated contrast required for adequate image quality in DE-CTPA examinations.

Optimization of keV-settings in abdominal and lower extremity dual-source dual-energy CT angiography determined with virtual monoenergetic imaging

OBJECTIVES To compare objective image quality indices in dual-energy CT angiography (DE-CTA) studies of the abdomen and lower extremity using conventional polyenergetic images (PEIs) and virtual monoenergetic images (MEIs) at different kiloelectron volt (keV) levels. METHODS We retrospectively evaluated 68 dual-source DE-CTA studies. 50 patients (42 men, 71 ± 10 years) underwent abdominal DE-CTA. 18 patients (13 men, 67 ± 10 years) underwent lower extremity DE-CTA. MEIs from 40 to 120 keV were reconstructed. Signal intensity, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed in infrarenal aorta, superior mesenteric, external iliac, femoral, popliteal, and lower leg arteries. Comparisons between MEIs and PEIs were performed with Dunnetts test. RESULTS 222 arteries were evaluated. In abdominal arteries 70 keV MEIs showed statistically equal signal intensity, noise and CNR levels (+13%; +31%, -14% on average; all p>0.05) compared to PEIs; SNR was equal or slightly impaired (-7% on average; p<0.001-1.00). In lower extremity arteries 60 keV MEIs resulted in significantly higher signal intensity and CNR (+54%; +54% on average; all p<0.05) compared to PEIs at equal noise levels (+18% on average; all p>0.05) and equal or higher SNR (+49% on average; p<0.01-0.35). CONCLUSIONS Low-keV MEIs lead to equal or higher signal intensity and CNR compared to PEIs. In lower extremity DE-CTA, additional reconstruction of low-keV MEIs at 60 keV might increase diagnostic confidence.

Pulmonary embolism: CT signs and cardiac biomarkers for predicting right ventricular dysfunction

The aim of this study was to prospectively evaluate the accuracy of quantitative cardiac computed tomography (CT) parameters and two cardiac biomarkers (N-terminal-pro-brain natriuretic peptide (NT-pro-BNP) and troponin I), alone and in combination, for predicting right ventricular dysfunction (RVD) in patients with acute pulmonary embolism. 557 consecutive patients with suspected pulmonary embolism underwent pulmonary CT angiography. Patients with pulmonary embolism also underwent echocardiography and NT-pro-BNP/troponin I serum level measurements. Three different CT measurements were obtained (right ventricular (RV)/left ventricular (LV)axial, RV/LV4-CH and RV/LVvolume). CT measurements and NT-pro-BNP/troponin I serum levels were correlated with RVD at echocardiography. 77 patients with RVD showed significantly higher RV/LV ratios and NT-pro-BNP/troponin I levels compared to those without RVD (RV/LVaxial 1.68±0.84 versus 1.00±0.21; RV/LV4-CH 1.52±0.45 versus 1.01±0.21; RV/LVvolume 1.97±0.53 versus 1.07±0.52; serum NT-pro-BNP 6,372±2,319 versus 1,032±1,559 ng·L−1; troponin I 0.18±0.41 versus 0.06±0.18 g·L−1). The area under the curve for the detection of RVD of RV/LVaxial, RV/LV4-CH, RV/LVvolume, NT-pro-BNP and troponin I were 0.84, 0.87, 0.93, 0.83 and 0.70 respectively. The combination of biomarkers and RV/LVvolume increased the AUC to 0.95 (RV/LVvolume with NT-pro-BNP) and 0.93 (RV/LVvolume with troponin I). RV/LVvolume is the most accurate CT parameter for identifying patients with RVD. A combination of RV/LVvolume with NT-pro-BNP or troponin I measurements improves the diagnostic accuracy of either test alone.

First–Arterial-Pass Dual-Energy CT for Assessment of Myocardial Blood Supply: Do We Need Rest, Stress, and Delayed Acquisition? Comparison with SPECT

PURPOSE To compare the relative contributions of rest, stress, and delayed acquisitions with the accuracy of dual-energy (DE) computed tomography (CT) for the assessment of myocardial blood supply. MATERIALS AND METHODS With institutional review board approval and HIPAA compliance, 55 consecutive patients (10 women, 45 men; mean age, 62 years ± 10) clinically referred for cardiac single photon emission computed tomography (SPECT) who were known to have or were suspected of having coronary artery disease were prospectively enrolled. DE CT studies were acquired during adenosine stress, at rest, and after 6-minute delay. The DE CT iodine distribution maps were visually assessed for perfusion deficits or late iodine enhancement. Per-segment agreement between modalities was investigated with κ statistics. Test characteristics for the detection of perfusion deficits were calculated for combinations of rest, stress, and delayed DE CT acquisition, with SPECT as reference standard. RESULTS At SPECT, 714 segments were considered normal, 192 showed fixed perfusion defects, and 29 showed reversible perfusion deficits. Sensitivity of rest-only DE CT was 92%, and specificity was 98%. Stress-only, rest-stress, stress and delayed, and the combination of all three had a sensitivity of 99% and a specificity of 97%. Of 29 segments with reversible perfusion deficits at SPECT, 13 (45%) were misclassified by using rest-stress DE CT as fixed perfusion deficits. With stress DE CT plus delayed acquisition, 13 of 192 (7%) segments with fixed perfusion deficits at SPECT were misclassified as reversible. CONCLUSION Rest-stress acquisition should be the protocol of choice for assessment of the myocardial blood supply in DE CT. The accuracy of DE CT is not increased by the addition of a delayed DE CT acquisition, which may therefore be omitted to reduce radiation exposure. With rest-stress DE CT, almost one-half of defects that are reversible at SPECT were classified as fixed; radiologists and clinicians need to be aware of this incongruence when they interpret DE CT myocardial perfusion studies.

Diffusion and perfusion MRI of the lung and mediastinum.

With ongoing technical improvements such as multichannel MRI, systems with powerful gradients as well as the development of innovative pulse sequence techniques implementing parallel imaging, MRI has now entered the stage of a radiation-free alternative to computed tomography (CT) for chest imaging in clinical practice. Whereas in the past MRI of the lung was focused on morphological aspects, current MRI techniques also enable functional imaging of the lung allowing for a comprehensive assessment of lung disease in a single MRI exam. Perfusion imaging can be used for the visualization of regional pulmonary perfusion in patients with different lung diseases such as lung cancer, chronic obstructive lung disease, pulmonary embolism or for the prediction of postoperative lung function in lung cancer patients. Over the past years diffusion-weighted MR imaging (DW-MRI) of the thorax has become feasible with a significant reduction of the acquisition time, thus minimizing artifacts from respiratory and cardiac motion. In chest imaging, DW-MRI has been mainly suggested for the characterization of lung cancer, lymph nodes and pulmonary metastases. In this review article recent MR perfusion and diffusion techniques of the lung and mediastinum as well as their clinical applications are reviewed.

Quantification of left and right ventricular function and myocardial mass: comparison of low-radiation dose 2nd generation dual-source CT and cardiac MRI.

OBJECTIVE To prospectively evaluate the accuracy of left and right ventricular function and myocardial mass measurements based on a dual-step, low radiation dose protocol with prospectively ECG-triggered 2nd generation dual-source CT (DSCT), using cardiac MRI (cMRI) as the reference standard. MATERIALS AND METHODS Twenty patients underwent 1.5T cMRI and prospectively ECG-triggered dual-step pulsing cardiac DSCT. This image acquisition mode performs low-radiation (20% tube current) imaging over the majority of the cardiac cycle and applies full radiation only during a single adjustable phase. Full-radiation-phase images were used to assess cardiac morphology, while low-radiation-phase images were used to measure left and right ventricular function and mass. Quantitative CT measurements based on contiguous multiphase short-axis reconstructions from the axial CT data were compared with short-axis SSFP cardiac cine MRI. Contours were manually traced around the ventricular borders for calculation of left and right ventricular end-diastolic volume, end-systolic volume, stroke volume, ejection fraction and myocardial mass for both modalities. Statistical methods included independent t-tests, the Mann-Whitney U test, Pearson correlation statistics, and Bland-Altman analysis. RESULTS All CT measurements of left and right ventricular function and mass correlated well with those from cMRI: for left/right end-diastolic volume r=0.885/0.801, left/right end-systolic volume r=0.947/0.879, left/right stroke volume r=0.620/0.697, left/right ejection fraction r=0.869/0.751, and left/right myocardial mass r=0.959/0.702. Mean radiation dose was 6.2±1.8mSv. CONCLUSIONS Prospectively ECG-triggered, dual-step pulsing cardiac DSCT accurately quantifies left and right ventricular function and myocardial mass in comparison with cMRI with substantially lower radiation exposure than reported for traditional retrospective ECG-gating.