Low radiation dose subtraction CT angiography (CTA) for diagnosis of peripheral arterial occlusive disease

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1 Low radiation dose subtraction CT angiography (CTA) for diagnosis of peripheral arterial occlusive disease Poster No.: C-1978 Congress: ECR 2013 Type: Authors: Scientific Exhibit M. Suzuki 1, R. Tanaka 2, K. Yoshioka 2, S. Ehara 2 ; 1 Morioka/JP, 2 Iwate/JP Keywords: DOI: Calcifications / Calculi, Arteriosclerosis, Efficacy studies, Comparative studies, Image manipulation / Reconstruction, CT- Angiography, Vascular, Extremities, Arteries / Aorta /ecr2013/C-1978 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 15

2 Purpose Evaluation of stenosis in severely calcified arteries and high radiation dose due are major problems of conventional CT angiography (CTA) for peripheral arterial occlusive disease (PAOD). The aims of this study are to elucidate the efficacy of subtraction CTA compared with DSA and evaluate the radiation dose reduction and image quality of low radiation dose CTA. Methods and Materials # Comparison of percent stenosis between conventional CTA and DSA (fig.1) Patient population 37 consecutive patients (Male 33: Female 4, mean age 70.4±9.0 years old) with PAOD underwent conventional CTA and subsequent DSA to perform percutaneous transluminal angioplasty (PTA) during the period from January to December of Imaging protocol 320-rows multi-detector CT (Aquilion One, Toshiba Medical Systems, Nasu, JAPAN) was used in 16-rows helical scanning mode with 1-mm slice thickness. The slice thickness, pitch factor, gantry rotation time, and tube peak voltage were 1mm, , 0.5sec, and 120kVp, respectively. Also, adaptive dose reduction by tube current modulation was used and tube current was ranged from 75 to 125mAs. Contrast medium (350 or 370 mgi/ml iodine contrast) was injected via antecubital vein at 2mL/sec, total 65-75ml and immediately followed by 30mL saline flush. Automatic region of interest (ROI) threshold triggering technique was used. ROI was put to the top of abdominal aorta. When the contrast enhancement reached 200HU, the scanner automatically started. The scan range was set from the top of abdominal aorta to the ankle. The lower extremities of the patients were fixed with Vac-Lok patient immobilization system (MED-TEC) (fig.2). Subtraction images were calculated in each axial image and were reconstructed into S- CTA with maximum intensity projection (MIP) using by Zio workstation (Ziosoft). DSA was performed using a Philips Medical System (Allura Xper FD20/10, Bi-plane system, Netherlands) with an automated bolus chase protocol. Iodinated contrast material was injected via a straight 4Fr catheter inserted with a femoral artery puncture by using the Seldinger technique. Page 2 of 15

3 The percent stenosis analysis The percent stenosis of diseased arteries was measured in iliac and common femoral arteries (total 232 regions) with caliper methods (fig.3) in both S-CTA and DSA. # Comparison of radiation dose and image quality between conventional CTA and AIDR-3D (fig.4) Patient population 21 consecutive patients (Male 19: Female 2, mean age 72.62±8.66 years old) with PAOD underwent CTA with iterative reconstruction (IR) technique during the period from January to March of 2012 (IR group). On the other hand, 25 consecutive patients (Male 19: Female 6, mean age 70.84±9.88 years old) with PAOD underwent conventional CTA during the period from May to August of There was not significant difference between both two groups in BMI (IR group vs. Conv. group; 22.51±2.43 vs ±3.34 kg/m 2, p=0.74). CT protocol CT protocol was same as mentioned above except iterative reconstruction technique. AIDR-3D (Toshiba Medical Systems, Nasu, Japan) was used as an iterative reconstruction technique. The lowest tube current was set to 35mAs in IR group. The standard strength of AIDR-3D was used for the target SD as 35 at 1 mm slice thickness. CT data analysis The radiation doses per one scan and one exam were measured with dose length product (DLP). Also, in axial images, image noise, contrast and contrast noise ratio (CNR) were compared. The CT value of the abdominal aorta and the right erector spinae was measured in a ROI near the slice level of the celiac trunk. Image noise was defined as the standard deviation (SD) of CT value of the right erector spinae. Contrast was calculated as contrast= the CT value of the abdominal aorta - the right erector spinae. CNR was calculated as contrast/noise. Page 3 of 15

4 Images for this section: Fig. 1: The comparison with conventional CTA, subtraction CTA and DA. Both CTA were performed with conventional method. Page 4 of 15

5 Fig. 2: The system contains polystyrene beads, under the vacuum. The system gets hard and maintains its shape. Page 5 of 15

6 Fig. 3 Page 6 of 15

7 Fig. 4: The comparison with conventional CTA and IR-CTA. Page 7 of 15

8 Results #S-CTA had a positive correlation with DSA (R^2= ). For the stenosis analysis (#50%), subtraction CTA revealed a sensitivity, specificity, PPV and NPV of 96.9%, 92.2%, 82.9%, 98.7% (Table.1, fig.5). #The radiation doses were significantly lower in IR group than Conv. group (mean DLP per scan ± vs ± mgy/cm; p<0.001, mean DLP per exam ± vs ± mgy/cm; p<0.001) (Table.2). No significant differences in SD, contrast and CNR were observed between two groups (Table.3). Fig.6 showed images of IR group. Images for this section: Table 1 Page 8 of 15

9 Fig. 5 Page 9 of 15

10 Table 2 Page 10 of 15

11 Table 3 Page 11 of 15

12 Fig. 6: These images were performed with the methods as below. The lowest tube current was set to 35mAs and the standard strength of AIDR-3D was used for the target SD as 35 at 1 mm slice thickness. The left side was the image before the iterative reconstruction. In post-aidr 3D images, we can see small arteries (arrows) better than pre-aidr 3D image. Page 12 of 15

13 Conclusion Recently, CTA for PAOD as noninvasive procedures progressively replaced DSA of an invasive procedure (1). Met et al. reported the sensitivity of CTA for detecting more than 50% stenosis was 95%, and specificity was 96% (2). CTA is attractive due to its 3-D reconstruction and multiplanar ability, but CTA can be limited in the presence of calcification (3). Also, it needs high radiation doses because of the long scan range. Y.Watanabe et al. informed the orbital synchronized helical scan technique (OSHST) for evaluating intracranial aneurysms surgically treated with cobalt-alloy clips. OSHST was developed to permit 2 consecutive acquisitions along the same helical path, thereby reducing the misregistration between the 2 scans to enable acquisition of accurate subtraction images (4). We thought up applying this method for diagnosis of PAOD. We evaluated the efficacy of subtraction CTA compared with DSA. Also, we tried to decrease the radiation dose with iterative reconstruction methods (AIDR-3D). In our research, subtraction CTA, which is provided as a MIP image, had an accurate diagnostic ability for percent stenosis same as DSA, without using multiplanar reformation or axial images for evaluation. Also, AIDR-3D could reduce the radiation doses more than half to maintain the image quality. Subtraction CTA with iterative reconstruction is expected to become a useful tool for PAOD. However, we have not yet made a comparison between S-CTA with IR and DSA. Clinically, we are using S-CTA with IR and getting an impression that S-CTA with IR is as well as DSA (fig.7). Subtraction CTA is an accurate diagnostic tool for the evaluation of PAOD. Also, AIDR 3D can significantly reduce the radiation dose of peripheral CTA with maintaining the image quality. Subtraction CTA is an accurate diagnostic tool for the evaluation of PAOD. Also, AIDR 3D can significantly reduce the radiation dose of peripheral CTA with maintaining the image quality. Images for this section: Page 13 of 15

14 Fig. 7: The comparison with CTA, Subtraction CTA with IR and DA. Both CTA were performed with iterative reconstruction (AIDR-3D) method. We haven't yet made a comparison between S-CTA with IR and DSA in percent stenosis. However, we used S- CTA with IR clinically and got an impression that S-CTA with IR was possible to diagnose as well as DSA. Page 14 of 15

15 References 1. Levin DC, Rao VM, Parker L, et al. The effect of the introduction of MR and CT angiography on the utilization of catheter angiography for peripheral arterial disease. J Am Coll Radiol 2007; 4: Met R, Bipat S, Legemate DA, et al. Diagnostic performance of computed tomography in peripheral arterial disease: a systematic review and meta-anakysis. JAMA 2009; 301: Chan D, Anderson ME, Dolmatch BL. Imaging evaluation of lower extremity infrainguinal disease: role of the noninvasive vascular laboratory, computed tomography angiography, and magnetic resonance angiography. Tech Vasc Interv Radiol 2010; 13: Watanabe Y, Kashiwagi N, Yamada N et al. Subtraction 3D CT Angiography with the orbital synchronized helical scan technique for the evaluation of postoperative cerebral aneurysms treated with cobalt-alloy clips. Am J Neuroradiol: 29; Personal Information Page 15 of 15