Boris Schell

Intravenous contrast material administration at high-pitch dual-source CT pulmonary angiography: Test bolus versus bolus-tracking technique

PURPOSE To compare test bolus and bolus tracking for the determination of scan delay of high-pitch dual-source CT pulmonary angiography in patients with suspected pulmonary embolism using 50 ml of contrast material. MATERIALS AND METHODS Data of 80 consecutive patients referred for CT pulmonary angiography were evaluated. All scans were performed on a 128-channel dual-source CT scanner with a high-pitch protocol (pitch 3.0, 100 kV, 180 mAs). Contrast enhancement was achieved by injecting 50 ml of iomeprol followed by a saline chaser of 50 ml injected at a rate of 4 ml/s. The scan delay was determined using either the test bolus (n=40) or bolus tracking (n=40) technique. Test bolus required another 15 ml CM to determine time to peak enhancement of the contrast bolus within the pulmonary trunk. Attenuation profiles in the pulmonary trunk and on segmental level as well as in the ascending aorta were measured to evaluate the timing techniques. Additionally, overall image quality was evaluated. RESULTS In all patients an adequate and homogeneous contrast enhancement of more than 250 HU was achieved in the pulmonary arteries. No statistically significant difference between test bolus and bolus tracking was found regarding attenuation of the pulmonary arteries or overall image quality. However, using bolus tracking 15 ml CM less was injected. CONCLUSION A homogeneous opacification of the pulmonary arteries and sufficient image quality can be achieved with both the bolus tracking and test bolus techniques with significant lower contrast doses compared to conventional contrast material injection protocols.

High-pitch dual-source computed tomography pulmonary angiography in freely breathing patients.

Purpose: To investigate pulmonary arterial (PA) enhancement, image noise, and artifacts related to breathing and heart motion in patients with suspected pulmonary embolism. Materials and Methods: Seventy-six consecutive patients underwent computed tomographic pulmonary angiography (CTPA) in dual-source high-pitch mode (pitch 3.0, 100 kV, 180 mAs, 50 mL contrast material) without breathing commands. PA enhancement, image noise, signal to noise ratio, overall image quality, incidence of total or partial interruption of the contrast column in the PAs, and heart motion-related and breathing-related artifacts of the diaphragm and pulmonary structures were recorded. Results: Mean central and peripheral PA attenuation was 404±104 and 453±119 HU; mean image noise was 11±2 HU; mean examination time was 0.67±0.09 s; and mean dose-length product was 142±31 mGy cm. There were no motion artifacts of the diaphragm or pulmonary vessels related to breathing or heart motion. There was no case of partial or total interruption of the contrast column in the PA tree. No examination was rated nondiagnostic. Conclusions: High-pitch dual-source CTPA in freely breathing patients effectively produces images that are free of artifacts related to breathing and cardiac motion. Hence, Valsalva-related artifacts can be eliminated using this technique.

Triphasic contrast injection improves evaluation of dual energy lung perfusion in pulmonary CT angiography

PURPOSE Lung perfusion analysis at dual energy CT (DECT) is sensitive to beam hardening artifacts from dense contrast material (CM). We compared two scan and four CM injection protocols in terms of severity of artifacts and attenuation levels in the thoracic vessels. METHODS AND MATERIALS Data of 120 patients who had undergone dual source dual energy CT pulmonary angiography for suspected acute pulmonary embolism were evaluated. Group 1 (n=30) was scanned in craniocaudal direction using 64×0.6 mm collimation; groups 2-4 (n=30 each) were scanned in caudocranial direction using 14×1.2 mm collimation. In groups 1-3 biphasic injection protocols with different amounts of CM and NaCl were investigated. In group 4 a split-bolus protocol with an initial CM bolus of 50 ml followed by 30 ml of a 70%:30% NaCl/CM mixture and a 50 ml NaCl chaser bolus was used. CT density values in the subclavian vein (SV), superior vena cava (SVC), pulmonary artery tree (PA), and the descending aorta (DA) were measured. Artifacts arising from the SV and SVC on DE pulmonary iodine distribution map were rated on a scale from 1 to 5 (1=fully diagnostic; 5=non-diagnostic) by two blinded readers. RESULTS In protocol 4 mean attenuation in the SV (645±158 HU) and SVC (389±114 HU) were significantly lower compared to groups 1-3 (p<0.002). Artifacts in group 4 (1.1±0.4 and 1.5±0.7 for the SV and SVC, respectively) were rated significantly less severe compared to group 1 (3.2±1.0 and 3.0±1.1), 2 (2.6±1.1 and 2.3±1.0) and 3 (1.9±0.9 and 1.9±0.7) (p<0.01 for all), whereas no significant difference was found between groups 1 and 2 for the subclavian vein (p=0.07). Attenuation in the PA was also significantly lower in group 4 (282±116 HU) compared to group 1 (397±137 HU), group 2 (376±115 HU) and group 3 (311±104 HU), but still on a diagnostic level. CONCLUSION Split-bolus injection provides sufficient attenuation for pulmonary DECT angiography while beam hardening artifacts arising from high density contrast material in the thoracic vessels can be reduced significantly.

Effect of contrast material on image noise and radiation dose in adult chest computed tomography using automatic exposure control: A comparative study between 16-, 64- and 128-slice CT

PURPOSE To determine the difference in radiation dose between non-enhanced (NECT) and contrast-enhanced (CECT) chest CT examinations contributed by contrast material with different scanner generations with automatic exposure control (AEC). METHODS & MATERIALS Each 42 adult patients received a NECT and CECT of the chest in one session on a 16-, 64- or 128-slice CT scanner with the same scan protocol settings. However, AEC technology (Care Dose 4D, Siemens) underwent upgrades in each of the three scanner generations. DLP, CTDIvol and image noise were compared. RESULTS Although absolute differences in image noise were very small and ranged between 10 and 13 HU for NECT and CECT in median, the differences in image noise and dose (DLP: 16-slice:+2.8%; 64-slice:+3.9%; 128-slice:+5.6%) between NECT and CECT were statistically significant in all groups. Image noise and dose parameters were significantly lower in the most recent 128-slice CT generation for both NECT and CECT (DLP: 16-slice:+35.5-39.2%; 64-slice:+6.8-8.5%). CONCLUSION The presence of contrast material lead to an increase in dose for chest examinations in three CT generations with AEC. Although image noise values were significantly higher for CECT, the absolute differences were in a range of 3 HU. This can be regarded as negligible, thus indicating that AEC is able to fulfill its purpose of maintaining image quality. However, technological developments lead to a significant reduction of dose and image noise with the latest CT generation.

Scalar localization by computed tomography of cochlear implant electrode carriers designed for deep insertion.

Objectives This study aimed to evaluate the possibility of predicting radiologically the scalar localization of a 31.5-mm-long, free-fitting electrode carrier for cochlear implantation, using conventional planar computed tomography. Study Design A cross-sectional human temporal bone study was conducted. Setting Twenty human temporal bones were acquired postmortem and implanted with 31.5-mm-long electrode carriers. Ten of these were implanted into the scala tympani using the round window approach, whereas the other 10 electrodes were inserted into the scala vestibuli by cochleostomy. Computed tomography was then performed, and 2 experienced blinded radiologists evaluated the intracochlear position of the array. Main Outcome Measure The estimated position of the electrode carrier was described using a 5-point scale. After sectioning and histologic investigation, the results of the radiologic and histologic investigations were compared. Results In 17 of 20 cases, it was possible to estimate the correct position of the electrode carrier within the basal turn of the cochlea by means of computed tomography. As the insertion angles widened beyond 360 degrees, it became increasing difficult for the radiologists to correctly determine the position of the electrode carrier. Conclusion The comparison of our temporal bone experiment results with the computed tomography results revealed the difficulty of assessing the correct position of intracochlear electrodes. Scalar localization of deeply inserted electrode carriers cannot be precisely determined by means of computed tomography.

Reply to Letters to the Editor re: Low-dose computed tomography of the paranasal sinus and facial skull using a high-pitch dual-source system—First clinical results

Dear Editor, We appreciate the thorough analysis made by the authors of these two letters with regards to our original publication. In our study we noted amongst other things decreased CTDIvol (volume CT weighted dose index) and DLP (dose length product) values when using a second x-ray with increased table feed (dual source high-pitch mode). First, we agree that calibrations of CTDIvol values of the device are done on various phantoms by the vendor (head with 16 cm respectively body/chest with 32 cm in diameter). From that background, the concerns the authors raise appear to be coherent. Indeed our very own measurements given by the CT protocol show a significant lower dosage when using the high pitch-mode. Since that calibration was done on a body phantom and the mode was used in a head region, a correction of DLP values seems to be necessary. The electrocardiogram-gated highpitch examinations of the heart quoted by the authors were done using automated tube current control which raises the tube current with increasing pitch. This is contrary to our examination protocol where tube current output remains stable since no automatic exposure control was used. Yet to display the actual radiation dose of the proposed examination techniques, specific measurements of a head phantom equipped with thermoluminescent dosemeters (TLDs) would be necessary. This would also be necessary to define the contribution of the bowtie filter mentioned by the authors. However, this data is not available yet. We suggest that further studies should be performed analyzing the influence on the different phantoms and experiments using different shaped filters. The letters also draw attention to another issue regarding dose values given by CT devices. CTDIvol and DLP are routinely used to estimate radiation exposure of the patient. According to the “European Guidelines on Quality Criteria for CT” stated by the European Commission in 1999 dose reference levels are also given in terms of CTDIvol. However this value indicates energy imparted to a volume irrespective to the examined spatial pattern. This may not only lead to improper dosage results given by CT devices (e.g. with varying patient diameter) but can somewhat show falsely low results when using torso examination protocols for peripheral regions. Subsequently it is questionable whether the actual dose values shown by CT devices might nowadays function as a reasonable and reliable tool to estimate effective dose or to monitor examination protocols in terms of dose reference levels.