Split-bolus spectral CT imaging of the pancreas

Transcription

1 Split-bolus spectral CT imaging of the pancreas Poster No.: C-2620 Congress: ECR 2012 Type: Scientific Exhibit Authors: O. R. Brook, S. Gourtsoyianni, A. Brook, C. Wilcox, B Siewert, V. Raptopoulos ; Boston, MA/US, Athens/GR Keywords: Pathology, Contrast agent-intravenous, Image manipulation / Reconstruction, CT, Pancreas DOI: /ecr2012/C-2620 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 16

2 Purpose Pancreatic CTA is widely used for screening, detection, staging and follow up of the pancreatic cancer. The standard protocol used in our institution involves non contrast study, followed by pancreatic phase and portal venous phase. This combination of contrast phases provides perfect conspicuity of pancreatic tumor, proximity to vessels and detection of metastases. Nevertheless, multiple phases also cause very high levels of radiation exposure to the patients. Our goal as radiologists is to reduce the radiation exposure, due to the known risks of radiation exposure, without deterioration of the image quality and most importantly maintaining diagnostic value of the CT scan. Split bolus contrast administration is an established technique for a number of clinical indications most notably CT urography. The contrast is injected twice, while scanning is performed once only. This provides dual phase images in a single scan, for example nephrographic and excretory phase as in the case of CT urography. We propose implementation of split bolus technique for providing pancreatic and portal venous / parenchymal phase for pancreatic CTA. Monochromatic images acquired with spectral MDCT increase attenuation of the iodine containing tissues by using lower kvp due to increase in photoelectric absorption and reduction of the Compton scatter. Furthermore, it has been shown that conspicuity of the malignant pancreatic tumors is greater with 80kVp as compared to weighted average 120kVp, as acquired on the dual-energy scanner. The aim of current study was to evaluate the feasibility of combination of split bolus contrast injection with spectral MDCT protocol for pancreatic CTA, compared to the standard multiphasic polychromatic MDCT scan. Methods and Materials The study was conducted with the approval of institutional review board and was compliant with Health Insurance Portability and Accountability Act regulations. Informed consent was waived by the Institutional Review Board. In our institution, patients with high suspicion for pancreatic adenocarcinoma are referred to for pancreatic MDCT Angiography asfirst CTstudy. This study includes 144 consecutive patients referred for pancreatic CTA for suspected pancreatic neoplasm. These patients were assigned to either standard or split bolus spectral MDCT protocol Page 2 of 16

3 accordingly to scanner availability. Of those, 69 scans that were reported as normal on clinical interpretation by two radiologists in service comprised by a radiology resident and an experienced abdominal imager staff. These studies were reviewed again by one of the investigators (ORB, 8 years of experience in abdominal imaging) who confirmed the original interpretation. The patients were also considered as having normal pancreas by tentative clinical assessment based in part on the results of the CT scan were not include in any further analysis. One case with split bolus pancreatic CTA was excluded due to the poor quality. This patient was very obese (430 pounds) and a standard pancreatic CTA that was performed subsequently was also of low image quality. The remaining 74 patients with pancreatic lesions were included in this study. Of these, 38 had single bolus pancreatic CTA and 36 split bolus spectral imaging. Scanning Technique Split bolus spectral studies were performed on a 64-detector GE Discovery CT750 HD with Gemstone Spectral Imaging (General Electric Medical Systems, Milwaukee, WI). Standard protocol studies were performed on a 64-detector GE VCT scanner (General Electric Medical Systems, Milwaukee, WI). Standard protocol CT scan was obtained with filtered back projection reconstruction with non-contrast, late arterial (pancreatic) and portal venous phases. ASIR (Adaptive Statistical Iterative Reconstruction) of 30% was implemented to reduce the radiation dose in all phases. The low ma non-contrast scan was performed with helical scan, 120kVp, large SFOV, 200mA, noise index of 26, pitch 1.375, collimation of 64 x mm and reconstructed with slice thickness of 5mm and interval of 5mm. The late arterial (pancreatic) phase was scanned to include pancreas only with 120kVp, large SFOV, 675mA, NI (noise index) of 19, automatic tube current modulation, pitch 0.984, collimation of 64 x mm, and reconstructed with slice thickness of 2.5mm and interval of 2.5mm. Portal venous phase included the whole liver and was scanned with 120kVp, large SFOV, 600mA, NI of 13.88, automatic tube current modulation, pitch 1.375, rotation of 0.5 sec, collimation of 64 x mm, and reconstructed with slice thickness of 5mm and interval of 5mm. Bolus tracking was used to ascertain the late arterial phase, which was triggered 15 seconds after aortic enhancement reached 300HU. The portal venous phase was scanned 32 seconds after pancreatic phase or 75 seconds after initiation of contrast injection, whichever occurs earlier. Total of 140cc of contrast was injected at a rate of 4-5 cc/sec, followed by 40cc of saline chaser. Split bolus spectral CT scan was performed first with a low-ma non-contrast scan of the abdomen with 120kVp, large SFOV, 200mA, NI of 26, automatic tube current modulation, ASIR of 30%, pitch 1.375, collimation of 64 x 0.625mm and reconstructed with slice thickness of 5mm and interval of 5mm. This was followed by a single helical GSI-10 scan, performed with gemstone spectral acquisition (GSI), 140kVp, 600mA, automatic tube current modulation, pitch of 1.375, rotation of 0.8 sec, collimation of 64 x 0.625mm. The Page 3 of 16

4 spectral images were then reconstructed at 60keV and at 77kev; both with 2.5 mm slice width and interval. The split bolus protocol included two contrast injections separated by a short pause geared to provide a combined arterial-venous phase. First 100 cc of contrast was injected for the portal venous phase at approximately 70 sec and second 40 cc of contrast to boost the pancreatic phase at approximately 35 sec after the second injection. Empirically, with an injection rate of 5 cc/sec, the first dose of 100 cc lasts 20 sec; after a pause of 15 sec, a second dose of 40 cc lasts 8 sec and scan is done 35 sec after the second bolus (pancreatic phase) or 70 sec after the first bolus (portal venous phase). At the injection rate of 4 cc/sec the pause is set at 10 sec. The second bolus is followed by 40 cc of saline chaser. Based on these empirical delays, we used bolus tracking set after the initiation of the second bolus and set to start scanning 15 sec after the aorta reached 280HU. For both studies we used Omnipaque 350, (Iohexol, 350 mg/ml, GE Healthcare) with 4-5cc/sec injection rate into the antecubital fossa vein. Images for this section: Page 4 of 16

5 Fig. 1: Standard protocol used for pancreatic CTA in our instution consist of smart prep series to time the peak aortic enhancement. The pancreatic phase (late arterial phase) acquired at 15 seconds after the enhancement in the aorta reaches 280HU. The portal venous phase acquired 32 seconds after end of acquisition of pancreatic phase or 75 seconds from the initiation of contrast injection. Overall 140cc of iodinated contrast is used, followed by 40 cc saline chaser. Fig. 2: Split bolus spectral pancreatic CTA protocol used in our institution included a single scan acquired 15 seconds after aortic enhancement reaches 280HU or 75 seconds from the initiation of the contrast injection. The dual phase in a single scan is achieved by splitting the contrast bolus into 100cc and additional 40cc injected 15 seconds later. This is followed by 40cc saline chaser. Page 5 of 16

6 Results Fig. 3 References: O. R. Brook; Radiology, Boston, UNITED STATES OF AMERICA Page 6 of 16

7 Fig. 4 References: O. R. Brook; Radiology, Boston, UNITED STATES OF AMERICA Images for this section: Page 7 of 16

8 Fig. 5: Average attenuation of the aorta was not significantly different between arterial phase of the standard pancreatic CTA protocol (Figure 3A) and split bolus at 60keV (Figure 3B) (367.6 ± 95.8HU vs ± 138.0HU, p=0.6). Page 8 of 16

9 Fig. 6: The average attenuation of the main portal vein was significantly higher at 60keV of split bolus pancreatic CTA protocol, compared to the portal venous phase of standard pancreatic CTA protocol (374.1 ± 86.3HU vs ±61.3HU, p Page 9 of 16

10 Fig. 7: The average liver attenuation was higher at 60keV of the split bolus protocol (Figure 4B) than at portal venous phase of the standard pancreatic CTA protocol (192.1 ± 34.8HU vs ± 32.7HU, p Page 10 of 16

11 Fig. 8: The average tumor conspicuity (defined as difference between pancreas and tumor attenuation, excluding cystic tumors) was significantly higher at 60keV of split bolus pancreatic CTA protocol compared to the late arterial and portal venous phases of standard pancreatic CTA protocol (83.5 ± 54.5HU vs ± 25.4HU at pancreatic phase and 52.8 ± 29.2HU at portal venous phase, p Page 11 of 16

12 Fig. 9: Dose length product (DLP) in the standard protocol group was 1242 ± 612 mgy*cm and in the split bolus spectral protocol group 631 ± 47.2 mgy*cm (p Page 12 of 16

13 Conclusion In a single combined phase, split-bolus spectral imaging resulted in vascular, liver and pancreatic attenuation values and pancreatic tumor conspicuity equal or higher than those from a combination of two phase pancreatic imaging. Images for this section: Fig. 10: Split-bolus spectral CT of the pancreas Page 13 of 16

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16 Xue HD, Liu W, Sun H, Wang X, Chen Y, Su BY, Sun ZY, Chen F, Jin ZY. [Application of second generation dual-source computed tomography dual-energy scan mode in detecting pancreatic adenocarcinoma]. Zhongguo Yi Xue Ke Xue Yuan Xue Bao 2010;32(6): (Chinese) Personal Information O. R. Brook, A. Brook, C. Wilcox, B. Siewert, V. Raptopoulos Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA S. Gourtsoyianni Athens, Greece Page 16 of 16