Diagnostic value of time-resolved CT angiography for the lower leg.

OBJECTIVE: The aim of this study was to test the feasibility of time-resolved computed tomography angiography (TR-CTA) for use in the lower leg. METHODS: Fifty-nine patients with suspected peripheral arterial occlusive disease were examined with a standard CTA (S-CTA) of the lower run-off and with an additional TR-CTA of the calves (12 phases; 2.5 s/phase, 80 kV, 120 mAs, volume of contrast medium 50 mL, flow rate 5.0 mL/s). For seven lower-leg artery segments, arterial contrast and the presence of venous overlay were tested for S-CTA and TR-CTA. Stenoses were classified on a three-point scale separately for S-CTA and TR-CTA, and diagnostic confidence for stenosis assessment was evaluated for both datasets. Contrast arrival times and HU values were evaluated in patients with asymmetric proximal stenoses. RESULTS: TR-CTA resulted in significantly higher contrast enhancement (P < 0.0001) and less venous overlay as compared to S-CTA (P < 0.05). Diagnostic confidence for stenosis rating was significantly higher in TR-CTA (P < 0.0001). Asymmetric proximal stenoses lead to significantly delayed and diminished contrast enhancement on the stenotic side. CONCLUSION: TR-CTA of the calves is feasible and provides higher enhancement and higher diagnostic confidence as compared to monophasic CTA of the lower legs.

Feasibility and radiation dose of high-pitch acquisition protocols in patients undergoing dual-source cardiac CT.

OBJECTIVE: The objective of this study was to compare image quality and radiation dose between high-pitch and established retrospectively and prospectively gated cardiac CT protocols using an Alderson-Rando phantom and a set of patients. MATERIALS AND METHODS: An anthropomorphic Alderson-Rando phantom equipped with thermoluminiscent detectors and a set of clinical patients underwent the following cardiac CT protocols: high-pitch acquisition (pitch 3.4), prospectively triggered acquisition, and retrospectively gated acquisition (pitch 0.2). For patients with sinus rhythm below 65 beats per minute (bpm), high-pitch protocol was used, whereas for patients in sinus rhythm between 65 and 100 bpm, prospective triggering was used. Patients with irregular heart rates or heart rates of ≥ 100 bpm, were examined using retrospectively gated acquisition. Evaluability of coronary artery segments was determined, and effective radiation dose was derived from the phantom study. RESULTS: In the phantom study, the effective radiation dose as determined with thermoluminescent detector (TLD) measurements was lowest in the high-pitch acquisition (1.21, 3.12, and 11.81 mSv, for the high-pitch, the prospectively triggered, and the retrospectively gated acquisition, respectively). There was a significant difference with respect to the percentage of motion-free coronary artery segments (99%, 87%, and 92% for high-pitch, prospectively triggered, and retrospectively gated, respectively (p < 0.001), whereas image noise was lowest for the high-pitch protocol (p < 0.05). CONCLUSION: High-pitch scans have the potential to reduce radiation dose up to 61.2% and 89.8% compared with prospectively triggered and retrospectively gated scans. High-pitch protocols lead to excellent image quality when used in patients with stable heart rates below 65 bpm.

Time-resolved computed tomography imaging of the aorta: a feasibility study.

PURPOSE: The aim of this study was to test the feasibility and the additional value of time-resolved computed tomography angiography (CTA) of the aorta, using multiple low-dose phases. MATERIALS AND METHODS: Twenty-two consecutive patients underwent a time-resolved CTA protocol (TR-CTA) of the aorta, either for follow-up of endovascular aneurysm repair (EVAR) or aortic dissection, using a CT scanner with the possibility of bidirectional table movements for dynamic CT imaging (Siemens Definition AS+; 12 phases, temporal resolution 2.5 s/scan, 80 kVp, 120 mAs/rot, scan range 27 cm, 60 mL; Imeron 400, flow 5.0 mL/s). The patients had previously undergone standard CTA (120 kVp, 100 mL contrast agent). Standard CTA after EVAR and aortic dissection were triphasic and biphasic protocols, respectively. Effective radiation dose and maximum Hounsfield unit values were compared between the TR-CTA and standard CTA. Image quality was rated for TR-CTA. RESULTS: Fifteen patients underwent TR-CTA for follow-up after EVAR; 4 were examined for follow-up after dissection and 3 for both, that is, aortic dissection treated with an endovascular stent. Mean effective dose of TR-CTA for the scan range of 27 cm (15.3+/-1.1 mSv) was comparable with the biphasic standard CTA protocols (16.2+/-2.4 mSv; P=0.29). Triphasic protocols resulted in 23.7+/-4.9 mSv (P<0.0001). Hounsfield unit values were not significantly different. Most of the examinations (91%) were fully evaluable, whereas 9% were of limited evaluability because of high image noise. None of the examinations was nondiagnostic. DISCUSSION: TR-CTA consisting of multiple low-dose phases leads to a clear depiction of the angiographic information and is feasible for follow-up after EVAR and aortic dissection. Considering the limited scan range, radiation dose is comparable with the standard biphasic CTA protocol, but dynamic information may provide additional information.