Research Report

Comparison of gastric vascular anatomy by monochromatic and polychromatic dual-energy spectral computed tomography imaging

Journal of International Medical Research 2014, Vol. 42(1) 26–34 ! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0300060513504703 imr.sagepub.com

Yamin Wan1,*, Zhizhen Li2,*, Nina Ji1 and Jianbo Gao1

Abstract Objective: To evaluate the use of monochromatic and polychromatic dual-energy spectral computed tomography (CT) imaging for preoperative assessment of gastric vascular anatomy. Methods: Patients with suspected gastric cancer underwent spectral CT to generate conventional 140 kVp polychromatic and monochromatic images with energy levels ranging from 40 to 140 keV during the late arterial and portal venous phases. Optimal monochromatic images were selected according to the contrast-to-noise ratio (CNR) for the gastric artery. Image quality was subjectively assessed. Display rates of the arteries were recorded. Results: The study included 64 patients. Monochromatic images at 53  3 keV provided the optimum CNR. At this energy level, subjective image scores were significantly higher for monochromatic images than polychromatic images. There were no significant differences in the display rates of arteries between polychromatic and optimal monochromatic images. Conclusions: Monochromatic images obtained with spectral CT can improve the visualization of gastric arteries.

Keywords spectral computed tomography, monochromatic image, gastric artery, computed tomography angiography Date received: 29 July 2013; accepted: 18 August 2013

*These authors contributed equally to this article. 1

Department of Radiology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China 2 Department of Endocrinology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China

Corresponding author: Jianbo Gao, Department of Radiology, The First Affiliated Hospital of Zhengzhou University, 1 East Jianshe Road of ErQi District, Zhengzhou, Henan 450052, China. Email: [email protected]

Wan et al.

Introduction Gastric cancer is one of the most common cancers worldwide. It accounts for approximately 8% of new cancers, with an incidence of 989 600 and mortality rate of 738 000 per year.1 Careful determination of each patient’s anatomy before gastric cancer surgery is essential due to the complex branching patterns and morphology of gastric blood vessels.2 Accurate identification of feeding arteries, vascular invasion and artery variation is essential to avoid vascular injury, and minimize bleeding and the duration of surgery.2 Computed tomography angiography (CTA) is a minimally invasive procedure for observing vascular structures. Multidetector computed tomography (MDCT) angiography is routinely used for diagnosis and management of patients with abdominal aortic aneurysms3,4 and other vascular pathologies and tumours.5–9 MDCT allows visualization of gastric tumours10 and assessment of stereoscopic vessel anatomy,11 exposing the organs involved from any viewpoint. The display rate of larger diameter arteries (e.g. the left gastric artery [LGA] and right gastroepiploic artery [RGEA]) approaches 100%, but those of smaller diameter arteries (e.g. the right gastric artery [RGA], left gastroepiploic artery [LGEA], short gastric artery [SGA] and posterior gastric artery [PGA]) are lower.12 Spectral CT allows the reconstruction of conventional polychromatic images corresponding to 140 kVp, as well as monochromatic images with energies ranging from 40 to 140 keV. This procedure also reduces beam-hardening artefacts and optimizes contrast via selectable monochromatic energy (keV).13–15 The potential benefits of spectral CT include increased vessel attenuation at lower energies.16,17 The aims of this study, therefore, were to evaluate the use of spectral CT for improving image quality, and to select the optimal single energy level that

27 provides the best contrast-to-noise ratio (CNR) for displaying gastric arteries.

Patients and methods Study population The study recruited patients with suspected gastric cancer undergoing CT at the Department of Radiology, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China, between May 2011 and December 2011. Inclusion criteria were: (i) MDCT performed within 14 days before gastrectomy (if required); (ii) no preoperative treatment. Patients with iodine allergy or cardiac, renal or hepatic insufficiency were excluded. Diagnosis was confirmed by biopsy or surgery. The study was conducted in accordance with the Declaration of Helsinki and was approved by the ethics committee of Zhengzhou University, Zhengzhou, China. Written informed consent was obtained from all participants.

Computed tomography Patients were required to fast for a minimum of 5 h prior to CT examination. At 10 min before CT, patients drank 1 l of water and received 20 mg scopolamine intramuscular injection to minimize peristaltic bowel movement. Patients were then placed in the supine position. Dual-phase contrast-enhanced scans were performed using the dual-energy spectral CT mode with a single tube, rapid, dual kVp (80 and 140 kVp) switching technique on a high-definition scanner (Discovery CT 750HD; GE Healthcare, Little Chalfont, UK). The scan encompassed the region from the top of the liver to the lower sides of both kidneys. Imaging parameters were: collimation thickness, 0.625 mm; acquisition slice thickness, 1.25 mm; tube current, 600 mA; rotation speed (gantry rotation time), 0.6 s; and helical pitch, 0.984 : 1. Patients then received 1.5 ml/kg non-ionic

28 contrast medium (OptirayTM 320; Tyco Healthcare, Neuhausen am Rheinfall, Switzerland) intravenous injection at a rate of 3–4 ml/s (total volume 90–120 ml) during the arterial and portal venous phases. The arterial phase imaging delay was determined by the automated image-triggering software (SmartPrep; GE Healthcare), and arterial phase imaging automatically began 12 s after the trigger attenuation threshold (100 HU) reached the level of the supracoeliac abdominal aorta. Portal venous phase imaging began 30 s after the arterial phase imaging.

Image analysis An abdominal radiologist (Y.W.) used a spectral imaging viewer (GSI Viewer; GE Healthcare) to review polychromatic image sets corresponding to conventional 140 kVp imaging, and monochromatic image sets corresponding to photon energies ranging from 40 to 140 keV. The arterial phase was used for analysis. The gastric artery CNR was determined using both the polychromatic and monochromatic axial images. To obtain the optimal keV images, circular regions of interest were placed on the base of the coeliac trunk and the gastric wall of the same slice (Figure 1A). The GSI Viewer automatically calculated and displayed the CNR values for the realtime monochromatic images. The optimal monochromatic level for generating the best CNR between the gastric artery and the gastric wall was selected from the CNR plot. Regions of interest were placed on the base of the coeliac trunk, the gastric wall and the subcutaneous fat tissue in the abdomen of the same slice to measure the CT value in both the optimal monochromatic images and the 140 kVp polychromatic images. The attenuation values were obtained in a manually defined 1–2 cm2 region of interest (ROI). Images were magnified, and care was

Journal of International Medical Research 42(1) taken to avoid calcified areas. The ROI was maintained to be as large as possible. CNR was defined as: ROIo  ROId)/SDn, where ROIo is the CT value of the base of the coeliac trunk, ROId is the CT value of the gastric wall of the same slice and SDn is the standard deviation of the subcutaneous fat tissue in the abdomen of the same slice.18 Final ROI values were the mean of three independent measurements. Overall subjective image quality was independently assessed by two investigators (J.G. and Y.W.) using volume rendering and thin slice maximum intensity projection. Disagreement was resolved by consensus. The rate of display of the LGA, RGA, LGEA, RGEA, SGA and PGA were recorded. Subjective image quality was evaluated using a five-point scale based on artery visualization and image noise: 5, excellent (arteries were clearly visible and the margins were sharp, no obvious image noise or artefacts); 4, superior (the arterial stem was clearly visible but the end was blurred, mild image noise or artefacts); 3, diagnostic (arteries were light, moderate image noise or artefacts, optimal enhancement but insufficient for accurate diagnosis); 2, suboptimal (only the distribution of the arteries was recognised, severe image noise or artefacts, inadequate for diagnosis); and 1, poor (vessels not seen, severe image noise and artefacts, no diagnosis possible) (Figure 2).

Statistical analyses Data were presented as mean  SD or n (%). CT values of the coeliac trunk were compared using paired t-test, and subjective scores were compared using paired t-test. Fisher’s exact probability test was used to compare the rates of display of gastric arteries on volume rendering from the optimal monochromatic and polychromatic images. All statistical calculations were performed using SPSSÕ version 13.0 (SPSS

Figure 1. Selecting the optimal contrast-to-noise ratio (CNR) in monochromatic computed tomography angiography of the gastric artery. (A) Axial image showing regions of interest (arrows) at the base of the coeliac trunk and normal gastric wall. (B) GSI Viewer analysis indicating that optimal CNR was achieved at 53 keV.

Wan et al. 29

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Journal of International Medical Research 42(1) Table 1. Subjective image scores of optimal monochromatic (53 keV) gastric arterial computed tomography angiography (CTA) and polychromatic (140 kVp) gastric arterial CTA in patients with suspected gastric cancer (n ¼ 64). Scan type

Figure 2. Subjective evaluation of computed tomography angiography of a patient with chronic gastritis. (A) Conventional polychromatic imaging, and (B) monochromatic imaging. The left gastroepiploic artery (LGEA) was more clearly visible in (B) than in (A) (subjective image scores 4 and 3, respectively). The subjective scores of the left gastric artery (LGA), right gastric artery (RGA), right gastroepiploic artery (RGEA) and splenic artery (SA) were 5 in the monochromatic image (B) and 4 in the conventional polychromatic image (A).

Inc., Chicago, IL, USA) for WindowsÕ . P-values < 0.05 were considered statistically significant.

Results The study recruited 64 patients with suspected gastric cancer (46 male/18 female; mean age 61.2 years (range 27 to 79 years). A total of 45 patients had gastric cancer, nine had gastrointestinal stromal tumours, six had gastric lymphoma and four had chronic gastritis. The optimal CNR for visualizing the gastric arteries in monochromatic images

Artery

Optimal monochromatic

Polychromatic

LGA RGA LGEA RGEA PGA SGA Mean

3.73  0.44 2.39  1.55 2.35  0.72 3.48  0.63 0.20  0.70 0.60  1.09 2.13  0.47

2.97  0.55*** 1.64  1.33*** 1.5  0.77*** 2.89  0.79*** 0.12  0.44* 0.38  0.85** 1.57  0.41***

Data presented as mean  SD. Image scores were valuated using a five-point scale based on artery visualisation and image noise: 5, excellent (arteries were clearly visible and the margins were sharp, no obvious image noise or artefacts), and 1, poor (vessels not seen, severe image noise and artefacts, no diagnosis possible). LGA, left gastric artery; RGA, right gastric artery; LGEA, left gastroepiploic artery; RGEA, right gastroepiploic artery; PGA, posterior gastric artery; SGA, short gastric artery. *P < 0.05, **P < 0.01 and ***P < 0.001 versus optimal monochromatic; paired-samples t-test.

was 53  3 keV (Figure 1B). The subjective scores for the optimal monochromatic and polychromatic images are shown in Table 1. These scores were significantly higher in optimal monochromatic images than polychromatic images (P < 0.05 for each comparison; Table 1). Table 2 shows data regarding mean CT values, CNRs and image noise of the coeliac trunk. All parameters were significantly higher in optimal monochromatic imaging than polychromatic imaging (P < 0.001 for each comparison; Table 2). Optimal monochromatic imaging allowed the visualization of smaller vessels than was possible with polychromatic imaging (Figure 3). There were no significant differences in the display rates of any artery on volume

Wan et al.

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Table 2. Computed tomography parameters in optimal monochromatic (53 keV) gastric arterial computed tomography angiography (CTA) and polychromatic (140 kVp) gastric arterial CTA in patients with suspected gastric cancer (n ¼ 64). Scan type Parameter

Optimal monochromatic

Polychromatic

Attenuation, 654.68  120.17 291.44  51.29*** HU CNR 36.96  11.76 20.87  7.32*** Noise 16.80  4.73 12.70  3.58*** Data presented as mean  SD. CNR, contrast-to-noise ratio. ***P < 0.001 versus optimal monochromatic; pairedsamples t-test.

rendering (VR) images generated using optimal monochromatic or polychromatic modes (Table 3 and Figure 4).

Figure 3. Computed tomography angiography of a 73-year-old man with gastric carcinoma. Optimal monochromatic imaging at 53 keV (B) allowed the visualization of smaller vessels than was possible with polychromatic imaging (A). LGA, left gastric artery; RHA, right hepatic artery; SMA, superior mesenteric artery.

Discussion Dual-energy CT (DECT) and spectral CT extend the capabilities of conventional CT and provide additional tools for vascular analysis.19–21 The single tube, rapid dualtube voltage switching technique of CT spectral imaging provides monochromatic images that depict how an imaged object would appear if the X-ray source produced single energy X-ray photons, resulting in high contrast resolution.14 DECT imaging at 70 keV has been shown to yield lower noise and higher image quality than conventional CT.19 In addition, image quality and CNR of intra- and extrahepatic portal veins were improved with spectral CT imaging at 51 keV.13 The optimal energy for gastric artery CNR was approximately 53 keV in the present study. Optimal monochromatic scanning resulted in significantly better vascular opacification than that seen with polychromatic imaging, as determined by subjective

Table 3. Rate of display of gastric arteries in optimal monochromatic (53 keV) gastric arterial computed tomography angiography (CTA) and polychromatic (140 kVp) gastric arterial CTA in patients with suspected gastric cancer (n ¼ 64). Scan type Parameter

Optimal monochromatic

Polychromatic

LGA RGA LGEA RGEA PGA SGA

64 (100.0) 46 (71.9) 55 (85.9) 64 (100.0) 7 (10.9) 14 (21.9)

64 (100.0) 42 (65.6) 50 (78.1) 64 (100.0) 7 (10.9) 10 (15.6)

Data presented as n (%). LGA, left gastric artery; RGA, right gastric artery; LGEA, left gastroepiploic artery; RGEA, right gastroepiploic artery; PGA, posterior gastric artery; SGA, short gastric artery. No statistically significant differences (P  0.05; Fisher’s exact probability test).

Figure 4. Volume rendering computed tomography angiography of a 62-year-old male patient with gastric carcinoma indicating similar artery visualization in both (A) polychromatic image and (B) optimal monochromatic image at 53 keV. CHA, common hepatic artery; GDA, gastroduodenal artery; LGA, left gastric artery; LGEA, left gastroepiploic artery; PHA, proper hepatic artery; RGA, right gastric artery; RGEA, right gastroepiploic artery; SA, splenic artery.

32 Journal of International Medical Research 42(1)

Wan et al. image analysis. The utility of CTA is largely determined by CNR. Although image noise was significantly higher in optimal monochromatic scanning than polychromatic mode in the current study, the monochromatic images had significantly higher subjective scores. This may be due to higher intravascular attenuation, and introduces the possibility of performing vascular studies using DECT with lower contrast medium and iodine dose. The current observations were similar to those of others.22 The rates of display of LGEA, RGA and SGA were slightly higher in optimal monochromatic images than polychromatic images in the present study, but these differences were not statistically significant. The present study found that DECT allowed radiologists to select an optimal imaging plane to accurately evaluate the gastric arteries. In addition, the use of a monochromatic X-ray beam reduces beam-hardening artefacts and attenuation effects commonly seen in conventional CT scans with polychromatic X-ray beams.23 Studies have indicated an optimal monochromatic energy of 72  5 keV for gastric cancers.24 Thus, a combination of images at approximately 50 and 70 keV could fulfil the dual objectives of higher contrast for vascular imaging and lower noise for evaluating gastric lesions. The use of different energies of spectral CT may contribute to more accurate evaluation, particularly when contrast enhancement is poor.17 DECT may provide new opportunities for detailed preoperative evaluation of gastric morphology and the vascularity of primary lesions. This finding may lead to opportunities for reducing radiation dose in the future. This study had several notable limitations. First, this investigation was a preliminary study with a relatively small number of patients, and further prospective clinical trials are required to validate our results. Secondly, one region of interest was placed on the base of the coeliac trunk instead of

33 the gastric artery. This had no effect on the results, however, since the attenuation of the arteries was >150 HU and there is little distinction between the coeliac trunk and gastric artery at >150 HU. Finally, this study did not investigate gastric veins, but further studies are currently underway. In conclusion, monochromatic images obtained with spectral CT can enhance the attenuation of iodine contrast media at certain energy levels. These monochromatic images can improve the visualization of gastric arteries.

Declaration of conflicting interest The authors declare that there are no conflict of interests.

Funding This research received no specific grant from any funding agency in the public, commercial or notfor-profit sectors.

References 1. Jemal A, Bray F, Center MM, et al. Global cancer statistics. CA Cancer J Clin 2011; 61: 69–90. 2. Matsuki M, Tanikake M, Kani H, et al. Dualphase 3D CT angiography during a single breath-hold using 16-MDCT: assessment of vascular anatomy before laparoscopic gastrectomy. Am J Roentgenol 2006; 186: 1079–1085. 3. Go¨rich J, Rilinger N, Sokiranski R, et al. Endoleaks after endovascular repair of aortic aneurysm: are they predictable? – initial results. Radiology 2001; 218: 477–480. 4. Armerding MD, Rubin GD, Beaulieu CF, et al. Aortic aneurysmal disease: assessment of stent-graft treatment-CT versus conventional angiography. Radiology 2000; 215: 138–146. 5. Chao CP, Walker TG and Kalva SP. Natural history and CT appearances of aortic intramural hematoma. Radiographics 2009; 29: 791–804.

34 6. Hayashi H, Matsuoka Y, Sakamoto I, et al. Penetrating atherosclerotic ulcer of the aorta: imaging features and disease concept. Radiographics 2000; 20: 995–1005. 7. Pipitone N, Versari A and Salvarani C. Role of imaging studies in the diagnosis and follow-up of large-vessel vasculitis: an update. Rheumatology (Oxford) 2008; 47: 403–408. 8. Chung JW, Kim HC, Choi YH, et al. Patterns of aortic involvement in Takayasu arteritis and its clinical implications: evaluation with spiral computed tomography angiography. J Vasc Surg 2007; 45: 906–914. 9. Kertesz JL, Anderson SW, Murakami AM, et al. Detection of vascular injuries in patients with blunt pelvic trauma by using 64-channel multidetector CT. Radiographics 2009; 29: 151–164. 10. Ott DJ. Virtual gastroscopy: a new look at the stomach. Am J Gastroenterol 2000; 95: 1084–1085. 11. Shioyama Y, Kimura M, Horihata K, et al. Peripancreatic arteries in thin-section multislice helical CT. Abdom Imaging 2001; 26: 234–242. 12. Lee SW, Shinohara H, Matsuki M, et al. Preoperative simulation of vascular anatomy by three-dimensional computed tomography imaging in laparoscopic gastric cancer surgery. J Am Coll Surg 2003; 197: 927–936. 13. Zhao LQ, He W, Li JY, et al. Improving image quality in portal venography with spectral CT imaging. Eur J Radiol 2011; 81: 1677–1681. 14. Lv P, Lin XZ, Li J, et al. Differentiation of small hepatic hemangioma from small hepatocellular carcinoma: recently introduced spectral CT method. Radiology 2011; 259: 720–729. 15. Lv P, Lin XZ, Chen K, et al. Spectral CT in patients with small HCC: investigation of image quality and diagnostic accuracy. Eur Radiol 2012; 22: 2117–2124. 16. Chandarana H, Godoy MC, Vlahos I, et al. Abdominal aorta: evaluation with dual-source dual-energy multidetector CT

Journal of International Medical Research 42(1)

17.

18.

19.

20.

21.

22.

23.

24.

after endovascular repair of aneurysms – initial observations. Radiology 2008; 249: 692–700. Okayama S, Seno A, Soeda T, et al. Optimization of energy level for coronary angiography with dual-energy and dualsource computed tomography. Int J Cardiovasc Imaging 2012; 28: 901–909. Spielmann AL, Nelson RC, Lowry CR, et al. Liver: single breath-hold dynamic subtraction CT with multi-detector row helical technology feasibility study. Radiology 2002; 222: 278–283. Matsumoto K, Jinzaki M, Tanami Y, et al. Virtual monochromatic spectral imaging with fast kilovoltage switching: improved image quality as compared with that obtained with conventional 120-kVp CT. Radiology 2011; 259: 257–262. Godoy MC, Naidich DP, Marchiori E, et al. Single-acquisition dual-energy multidetector computed tomography: analysis of vascular enhancement and postprocessing techniques for evaluating the thoracic aorta. J Comput Assist Tomogr 2010; 34: 670–677. Wang Q, Shi G, Liu X, et al. Optimal contrast of computed tomography portal venography using dual-energy computed tomography. J Comput Assist Tomogr 2013; 37: 142–148. Pinho DF, Kulkarni NM, Krishnaraj A, et al. Initial experience with single-source dual-energy CT abdominal angiography and comparison with single-energy CT angiography: image quality, enhancement, diagnosis and radiation dose. Eur Radiol 2013; 23: 351–359. Boll DT, Patil NA, Paulson EK, et al. Focal cystic high-attenuation lesions: characterization in renal phantom by using photoncounting spectral CT-improved differentiation of lesion composition. Radiology 2010; 254: 270–276. Pan Z, Pang L, Ding B, et al. Gastric cancer staging with dual energy spectral CT imaging. PLoS One 2013; 8: e53651.

Comparison of gastric vascular anatomy by monochromatic and polychromatic dual-energy spectral computed tomography imaging.

To evaluate the use of monochromatic and polychromatic dual-energy spectral computed tomography (CT) imaging for preoperative assessment of gastric va...
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