Clinical study
Image Quality of Virtual Noncontrast Images Derived from Dual-energy CT Angiography after Endovascular Aneurysm Repair

https://doi.org/10.1016/j.jvir.2009.10.040Get rights and content

Purpose

To compare true and “virtual” noncontrast images derived from dual-energy CT examinations in patients after endovascular repair of aortic aneurysms.

Materials and Methods

Seventy dual-energy CT examinations were performed on a dual-source CT scanner with a single-energy noncontrast scan and a dual-energy acquisition in venous phase. True and virtual noncontrast images were compared regarding image quality, calcifications in true noncontrast images, subtraction of calcification in virtual noncontrast images, and acceptance levels by two radiologists. Presence of endoleaks was assessed on venous-phase images and on virtual or true noncontrast images. In addition, the acceptance of color-coded images, in which iodine information is colored, was assessed. Possible dose reduction of a single-phase dual-energy examination protocol was compared with a standard biphasic examination protocol.

Results

Twenty-four endoleaks were detected and correctly classified with both approaches. Mean image quality was rated good for virtual noncontrast images (1.97 ± 0.99) and excellent for true noncontrast images (1.16 ± 0.37; P< .0001). Ninety-four percent of virtual noncontrast images were rated as diagnostic, and 80% of all true noncontrast images showed calcifications within the aneurysm. Subtraction of calcification in virtual noncontrast images was classified as none (30%), minimal (40%), moderate (24%), or severe (6%). Eighty-three percent of color-coded images were rated as fully diagnostic, 11% were accepted with restrictions, and 6% were nondiagnostic. Possible dose reduction of a single-phase dual-energy protocol, compared with a standard biphasic protocol, was 44%.

Conclusions

Dual-energy CT makes a reliable detection of endoleaks feasible in a single acquisition. This provides a potential dose reduction for patients who have to undergo lifelong follow-up examinations after endovascular aneurysm repair.

Section snippets

Patient Population

Between July 2007 and September 2008, 58 patients (48 men, 10 women; average age, 69.9 years ± 9.4; range, 47–75 y) underwent 70 dual-energy CT examinations after endovascular repair of aortic aneurysms. Time interval between EVAR and CT examination was 327 days ± 383. The study was approved by our institutional review board and all patients provided written informed consent prior to their participation in the trial.

For each patient, the body mass index was calculated (in kg/m2) by dividing

Patients

All patients underwent dual-energy CT without complications. Fifty of the patients had an abdominal, y-shaped stent-graft and eight had thoracic stent-grafts.

In session 1, with virtual noncontrast and dual-energy venous-phase imaging, 24 endoleaks were observed in 22 patients among the 70 CT examinations. Eight endoleaks were classified as type I (type Ia, n = 5; type Ib, n = 3). Eleven endoleaks were classified as type II (Fig 2) and five as type III. No cases of stent displacement or rupture

Discussion

Our quantitative and qualitative analysis of virtual noncontrast and true noncontrast images underlines that dual-energy CT–based virtual noncontrast images are a reasonable approximation of true unenhanced single-energy CT images, both in image quality parameters and in detection sensitivity for endoleaks. Although virtual noncontrast image quality is somewhat inferior, overall acceptance for diagnostic reading in patients who had undergone EVAR was good. Three nondiagnostic ratings were

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None of the authors have identified a conflict of interest.

1

W.H.S. and A.G. contributed equally to this work.

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