الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
MDCT is considered the first-line gold standard imaging test for diagnosing and staging of pancreatic lesions owing to its availability, rapid acquisition time and high sensitivity and specificity.(9, 11-14)
Despite recent improvements in conventional MDCT technology including improvement of temporal and spatial resolution and optimization of acquisition time in multiphasic imaging, pancreatic lesion imaging remains to be particularly challenging. These challenges include detection of early-stage pancreatic cancers, characterization of cystic lesions, demonstration of subtle enhancing portion within cystic lesions that denotes malignancy as well as detecting tiny neuroendocrine tumors candidate for resection. This could be attributed to the limited soft-tissue contrast of MDCT or to the limited difference in vascularity between pathological lesions and pancreatic parenchyma. Accordingly, if the contrast between pancreatic lesions and normal pancreatic parenchyma is improved on CT images, we may expect improved performance of CT in evaluation of pancreatic lesions.(164, 209) This could be possibly achieved using DECT technology. Because this technique allows concurrent acquisition of high and low energy data sets with the lower energy being closer to the k-edge of iodine, this will result in higher photon absorption and thus an increase in CT measurements in tissues that have taken up iodinated contrast compared to the surrounding tissues.(210, 211)
DECT can currently be performed using different approaches, based on either the x-ray tube output or detector. The available tube-based systems include dual source, fast kilovolt-switching, dual spin and split beam systems.(165, 243, 244)
Recently, dual-layer detector spectral CT has been introduced in clinical practice as the only available detector-based approach capable of simultaneous high and low energy data acquisition. For every scan, conventional (polyenergetic) images are obtained, in addition to simultaneous spectral data acquisition. This data can be used to generate a variety of spectral image sets including virtual monoenergetic, iodine density, Z effective and virtual non-contrast images.(203)
This study aimed to evaluate the role of dual-energy computed tomography in the detection and characterization of focal pancreatic lesions, through comparing different spectral image sets generated from dual-layer computed tomography to conventional images in detecting and characterizing focal lesions of the pancreas
In this study, we reviewed 54 patients with focal pancreatic lesions who underwent contrast-enhanced dual layer CT (iQon, Philips) scans of the abdomen for various clinical purposes.
Conventional, mono E, iodine density, iodine overlay and Z effective images were analyzed in the venous phase, which is the common phase acquired in all patients. Regions of interest were placed in the lesion, normal pancreas and retroperitoneal fat in conventional images and copied to MonoE (40-200KeV; 10KeV increment), iodine density and Z effective images. Lesion CNR and SNR, image noise as well as slopes of spectral curves were recorded. Subjective analysis of conventional, 40KeV, 50KeV, iodine density, iodine overlay and Z effective images was done using 4- point scales regarding image quality, lesion conspicuity and diagnostic confidence.
Sixty-four lesions were identified and their nature was verified by histopathology or a combination of follow-up CT, MRCP and/or EUS together with clinical data.
Among monoE images, 40KeV showed highest CNR and SNR (p<0.001) and was significantly higher compared to conventional images. Image noise was lower in all monoE images compared to conventional polyenergetic images (p<0.001).
Cystic, solid hypo- and hyper-vascular lesions were significantly different based on quantitative iodine concentration (p<0.01), Z effective numbers (p<0.01) and slope of spectral curve (p<0.01). However, iodine concentration displayed largest area under the curve in distinguishing between cystic and solid hypovascular lesions as well as between solid hypo- and hyper-vascular lesions.
Subjectively, 40KeV, 50KeV and iodine overlay images were markedly preferred over conventional images regarding image quality (p<0.01), lesion conspicuity (p<0.001) and diagnostic confidence (p<0.05). Lesion conspicuity was improved on Z effective images compared to conventional images in 31% of lesions, yet with no statistical significance (p>0.05). Lesion conspicuity of solid hypervascular lesions was clearly improved on Z effective images compared to conventional images (p<0.05), where 60% were rated strikingly evident (score 4) on Z effective images and none were rated 4 on conventional images.
In conclusion, based on our subjective analysis and substantiated by quantitative measurements we consider dual-layer CT a superior imaging choice over conventional CT for evaluating pancreatic lesions. Routine reconstruction of low KeV monoE, iodine overlay and Z effective images for supplementary use in clinical routine (whenever possible) can potentially improve focal pancreatic lesion detection and characterization.