Georg Mühlenbruch

Image fusion in dual energy computed tomography: effect on contrast enhancement, signal-to-noise ratio and image quality in computed tomography angiography.

Objective:The aim of this study was to evaluate the influence of different weighting factors on contrast enhancement, signal-to-noise ratio (SNR), and image quality in image fusion in dual energy computed tomography (DECT) angiography. Material and Methods:Fifteen patients underwent a CT angiography of the aorta with a SOMATOM Definition Dual Source CT (DSCT; Siemens, Forchheim, Germany) in dual energy mode (DECT) (tube voltage: 80 and 140 kVp; tube current: 297 eff. mA and 70 eff. mA; collimation, 14 × 1.2 mm). Raw data were reconstructed using a soft convolution kernel (D30f). Fused images were calculated using a spectrum of weighting factors (0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) generating different ratios between the 80- and 140-kVp images (eg, factor 0.5 corresponds to 50% image information from the 140- and the 80-kVp image). Both CT values and SNR were measured in the descending aorta (levels of celiac trunk, renal arteries, and aortic bifurcation), in the right and left common iliac artery and in paraaortal fat. Image quality was evaluated using a 5-point grading scale. Results were compared using paired t-tests and nonparametric paired Wilcoxon tests. Results:Statistically significant increases in mean CT values were seen in vessels when increasing weighting factors were used (all P ≤ 0.001). For example, mean CT values derived from the aorta at the level of the celiac trunk were 273.8 ± 25.8 Hounsfield units (HU), 304.0 ± 24.3 HU, 361.4 ± 22.5 HU, 418.3 ± 25.8 HU, 477.8 ± 32.2 HU, 536.2 ± 41.2 HU, 564.6 ± 45.3 HU, when the weighting factors 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 were used. The highest SNR values were found in vessels when the weighting factor 0.5 was used. The highest SNR values of the paraaortal fat were obtained for the weighting factors 0.3 and 0.5. Visual image assessment for image quality showed the highest score for the data reconstructed using the weighting factor 0.5. Conclusion:Different weighting factors used to create fused images in DECT cause statistically significant differences in CT value, SNR, and image quality. Best results were obtained using the weighting factor 0.5, which we recommend for image fusion in DECT angiography.

Low tube voltage improves computed tomography imaging of delayed myocardial contrast enhancement in an experimental acute myocardial infarction model.

Objective:We sought to evaluate the influence of tube voltage on the visualization of acute myocardial infarction (MI) in cardiac multislice spiral computed tomography (MSCT). Materials and Methods:Acute MI was induced in 12 domestic pigs by a 45-minute balloon occlusion of the left anterior descending artery. Delayed enhancement magnetic resonance imaging was performed 15 minutes after the injection of 0.2 mmol/kg Gd-DTPA. On the same day, retrospectively ECG-gated MSCT was performed at 120, 100, and 80 kV (16 × 0.75mm, 550mAseff.) 15 minutes after the injection of 140 mL of iopromide (1 g/iodine/kg). The pigs were killed and the hearts were excised and stained with 2,3,5-triphenyltetrazolium chloride. The area of acute MI, contrast-to-noise ratio (CNR), and percent signal difference were compared among the different imaging techniques by applying Bland-Altman plots and 2-way analysis of variance. Results:On MSCT at 120, 100, and 80 kV, the respective mean acute MI sizes were 18.4 ± 11.4%, 19.3 ± 11.5%, and 20.5 ± 11.6%. The mean MI sizes were 20.8 ± 12.2% and 20.1 ± 12.4% on magnetic resonance imaging and 2,3,5-triphenyltetrazolium chloride staining. Analysis of variance did not show any statistically significant differences between the different techniques with respect to the size of acute MI (P = 0.9880). Comparing the different kV settings on MSCT, the highest percent signal difference (74.7 ± 12.1%) and the highest CNR (6.7 ± 1.8) between infarcted and healthy remote myocardium were achieved at 80 kV. Conclusions:When compared with routine scan protocols, low tube voltage MSCT allows for the assessment of the MI size with an improved CNR and contrast resolution. This technique appears to be advantageous for assessing myocardial viability from contrast enhanced late-phase MSCT.

Uncarboxylated matrix Gla protein (ucMGP) is associated with coronary artery calcification in haemodialysis patients

Matrix gamma-carboxyglutamate (Gla) protein (MGP) is a potent local inhibitor of cardiovascular calcification and accumulates at areas of calcification in its uncarboxylated form (ucMGP). We previously found significantly lower circulating ucMGP levels in patients with a high vascular calcification burden. Here we report on the potential of circulating ucMGP to serve as a biomarker for vascular calcification in haemodialysis (HD) patients. Circulating ucMGP levels were measured with an ELISA-based assay in 40 HD patients who underwent multi-slice computed tomography (MSCT) scanning to quantify the extent of coronary artery calcification (CAC). The mean ucMGP level in HD patients (193 +/- 65 nM) was significantly lower as compared to apparently healthy subjects of the same age (441 +/- 97 nM; p < 0.001) and patients with rheumatoid arthritis (RA) without CAC (560 +/- 140 nM; p < 0.001). Additionally, ucMGP levels correlated inversely with CAC scores (r = -0.41; p = 0.009), and this correlation persisted after adjustment for age, dialysis vintage and high-sensitivity C-reactive protein (hs-CRP). Since circulating ucMGP levels are significantly and inversely correlated with the extent of CAC in HD patients, ucMGP may become a tool for identifying HD patients with a high probability of cardiovascular calcification.

Assessment of Global Right Ventricular Function on 64-MDCT Compared with MRI

OBJECTIVE The aim of this study was to compare ECG-gated 64-MDCT with MRI for the assessment of global right ventricular (RV) function from coronary CT angiography data. SUBJECTS AND METHODS Thirty-eight patients (25 men, 13 women; mean age +/- SD, 55.0 +/- 8.8 years) with suspected coronary artery disease underwent contrast-enhanced 64-MDCT (64 x 0.6 mm, 120 kV, 770 mAs(eff)) and 1.5-T MRI (balanced fast-field echo; TR/TE, 3.3/1.6; flip angle, 60 degrees ; 50 phases). Double oblique short-axis MDCT and MR images were used for further analysis. End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were computed from manually drawn endocardial contours of the right ventricle. For statistical analysis, repeated-measures analysis of variance and Pearsons correlation coefficients were calculated. Bland-Altman plots were computed. RESULTS In general, RV volumes calculated from 64-MDCT agreed well with those calculated from MRI. The mean EF (+/- SD) calculated from MDCT and MRI was 51.0% +/- 7.8% and 51.4% +/- 7.3%, respectively. An excellent correlation was observed for EDV (r = 0.99), ESV (r = 0.98), SV (r = 0.98), and EF (r = 0.97). Bland-Altman plots showed no systematic variation between MDCT and MRI data. No statistically significant differences (p < or = 0.05) between the techniques were found. CONCLUSION Although contrast injection is optimized for visualization of the coronary arteries, retrospectively ECG-gated 64-MDCT permits reliable assessment of global RV function.

Imaging of the Cardiac Venous System: Comparison of MDCT and Conventional Angiography

OBJECTIVE Diagnostic and therapeutic strategies in electrophysiology and interventional cardiology include the coronary venous system. The purpose of this study was to compare MDCT angiography with conventional coronary sinus angiography in terms of detailed anatomic display of the coronary veins. CONCLUSION MDCT angiography is a reliable alternative to conventional coronary sinus angiography for detailed anatomic display of the coronary veins.

Cardiac CT: coronary arteries and beyond

Multi-detector-row computed tomography (MDCT) has emerged as a rapidly developing method for non-invasive imaging of the heart. An understanding of ECG synchronization, contrast material administration, patient preparation and image post-processing is needed to optimize image quality. The basic technical principles and essentials of these technical basics are described here. Correctly applied cardiac MDCT allows imaging of the coronary arteries including coronary anatomy and stenosis detection. The same is true for evaluation of coronary artery bypass grafts and, to some extent, coronary artery stents. While quantification of total calcified plaque burden has been long established, coronary MDCT allows assessing plaque morphology and constitution. Recent approaches go beyond the coronaries and include evaluation of left ventricular function at rest and myocardial viability. In combination with experimental approaches for assessing aortic valve function and myocardial perfusion imaging, cardiac MDCT offers the potential for a comprehensive examination of the heart using a single breath-hold examination.

Dose Reduction during CT Fluoroscopy: Phantom Study of Angular Beam Modulation

PURPOSE To prospectively evaluate, in a phantom, the dose reductions achievable by using angular beam modulation (ABM) during computed tomographic (CT) fluoroscopy-guided thoracic interventions. MATERIALS AND METHODS To enable measurement of organ doses and effective patient dose, a female Alderson-Rando phantom was equipped with thermoluminescent dosimeters (TLDs) in 41 positions, with three TLDs in each position. Additionally, the local dose was assessed in 22 locations above the phantom to estimate the radiation exposure to the radiologists hand and the patients skin dose during thoracic interventions. Radiation exposure was performed with a 64-section multidetector CT scanner in the CT fluoroscopy mode, simulating a CT fluoroscopy-guided chest intervention. Effective dose, breast dose, and the dose to the radiologists hand during the simulated chest intervention were measured with and without ABM. Image noise as an indicator for image quality was compared for both settings. Statistical significance of the measured dose reductions and the image noise was tested by using the paired-samples t test, with P < .05 indicating a significant difference. RESULTS ABM significantly reduced the effective patient dose by 35%, the skin dose by 75%, the breast dose by 47% (P < .001 for all), and the physicians hand dose by between 27% (scattered radiation, P = .007) and 72% (direct radiation, P < .001). No significant difference was found in a comparison of the image noise with and that without ABM. CONCLUSION ABM leads to significant dose reductions for both patients and personnel during CT fluoroscopy-guided thoracic interventions, without impairing image quality.

Coronary artery calcium scoring with multislice computed tomography: in vitro assessment of a low tube voltage protocol.

Objectives:We sought to compare an 80-kVp coronary calcium scoring protocol with the standard protocol of 120 kVp in terms of accuracy and reproducibility and to assess its dose reduction potential. Materials and Method:An anthropomorphic heart phantom with calcium cylinders was scanned with different tube currents at 80 kVp and 120 kVp using a 16-slice multislice CT (MSCT) scanner. An adapted threshold for 80 kVp was calculated. Accuracy and reproducibility for calcium mass, volume, and Agatston score were analyzed using F-tests. The radiation doses needed to produce artifact-free images were determined. Results:Accuracy (measurement errors: mass 120 kVp +4.6%, mass 80 kVp −6.9%, volume 120 kVp +78.8%, volume 80 kVp +58.2%) and reproducibility (F-tests: mass: P = 0.4998, volume: P = 0.9168, Agatston: P = 0.5422) were comparable at both tube voltages. Avoiding the appearance of artificial lesions, a CTDIw,eff of 10.7 mGy was needed at 120 kVp versus 4.6 mGy at 80 kVp (dose reduction of 57%). Conclusions:Using an 80-kVp protocol in coronary calcium scoring, a relevant dose reduction is possible without compromising reproducibility and accuracy.

Automated volumetry of solid pulmonary nodules in a phantom: accuracy across different CT scanner technologies.

Objectives:The accuracy of automated volumetry for pulmonary nodules in a phantom using different CT scanner technologies from single-slice spiral CT (SSCT) to 64-slice multidetector-row CT (MDCT) was compared. Materials and Methods:A lung phantom with 5 different categories of pulmonary nodules was scanned using a single-slice spiral CT, a 4-slice MDCT, a 16-slice MDCT and a 64-slice MDCT. Each category comprised of 7–9 nodules each (total n = 40) with different known volumes. Standard dose and low dose protocols were performed using thin and thick collimation. Image data were reconstructed at the thinnest slice thickness. Data sets were analyzed with a dedicated volumetry software. Volumes of all nodules were calculated and compared. Results:Mean absolute percentage error (APE) for all nodules was 8.65% (±7.29%) for the SSCT, 10.26% (±8.25%) for the 4-slice MDCT, 8.19% (±7.57%) for the 16-slice MDCT and 7.89% (±7.39%) for the 64-slice MDCT. There was statistically significant influence of the scanner type, protocol, anatomic location, and nodule volume on APE, but overall, APEs were comparable. Conclusion:Computer-aided volumetry showed accurate measurements in all tested scanner types. This finding has important implications for nodule assessment and follow-up.

Coronary calcium scoring using 16-row multislice computed tomography: nonenhanced versus contrast-enhanced studies in vitro and in vivo.

Objectives:We sought to assess the agreement of coronary artery calcium score in nonenhanced and contrast-enhanced multislice-spiral computed tomography. Materials and Methods:Vessel phantoms and 36 patients underwent nonenhanced and contrast-enhanced cardiac multislice-spiral computed tomography (Sensation 16; Siemens, Germany). Reconstruction-parameters: slice thickness 3 mm, increment 2 mm, kernels B35f and B30f. The Agatston score, calcium mass, and number of lesions were calculated. Images were scored using detection thresholds of 130 Hounsfield units (HU) and 350 HU. Based on the Agatston score, risk stratification was performed. Results:In the phantom and patient study, altering the threshold from 130 to 350 HU led to a significant decrease in the mean Agatston score (phantom: 54.6%, patients: 66.7%) and calcium mass (33.0%, 47.0%) (B35f). Contrast-enhanced studies (threshold: 350 HU) showed an increase of the mean Agatston score (71.0%, 20.7%) and calcium mass (81.0%, 16.0%) when compared with nonenhanced scans (threshold: 350 HU). A total of 57% of all patients were assigned to different risk groups. Conclusions:Contrast material may simulate calcification; therefore, calculation of the coronary calcium score from contrast-enhanced images is not reliable.