Low-keV and Low-kVp CT for Positive Oral Contrast Media in Patients with Cancer: A Randomized Clinical Trial

Abstract

ositive oral contrast medium (OCM) is routinely used in the imaging of patients undergoing oncologic treatment and in patients after surgery for detecting extraluminal lesions and collections, defining anatomy, and assessing bowel integrity, especially in patients with insufficient visceral fat (1-3). Current oncology and American College of Radiology guidelines advocate the use of positive OCM, despite its influence on workflow (4,5). The latest-generation CT scanners provided by major manufacturers are equipped with two increasingly adopted techniques-namely, automated tube voltage (in kilovolt peaks) selection (ATVS) and dual-energy CT. This is because of well-established applications of these techniques that provide diagnostic image quality with high image contrast and enable material characterization (6-9). Both low-kVp and low-keV virtual monochromatic images (low-keV image reconstructions from dual-energy CT) augment the attenuation of iodine by two-to fourfold, and this property is being leveraged to reduce the dose of intravenous contrast medium (10-12). To achieve the average accepted enteral attenuation of 200 HU, a concentration of 13-15 mg iodine per milliliter (mg I/mL) iohexol or less than 3% wt/vol barium is routinely used in adults (13-16). At such OCM concentrations, low-kVp and low-keV images increase the intestinal luminal attenuation by up to 103% (17,18). This substantially higher attenuation of OCM creates challenges that may hinder adequate visualization of the bowel wall or adjacent structures and

Clinical Implementation of Dual-Energy CT for Gastrointestinal Imaging

“…Nevertheless, DECT further enhances the value of CT for bowel assessment in several clinical scenarios. When oral contrast material is used with DECT, reduction in oral contrast concentration by 25% or more can be useful to avoid excessive attenuation on low keV monochromatic images [63].…”

“…As DECT technology continues to evolve, multiple new technical innovations are anticipated to improve the value of multi-energy CT for evaluation of the gastrointestinal tract. Currently, groups are embracing the high sensitivity and quantitative nature of DECT to define useful thresholds for diagnoses, to expand its clinical applications [e.g., perfusion DECT for tumor characterization and treatment monitoring [76]; liver fibrosis [77]; DECT augmentation of suboptimal stool tagging during CT colonography [78] (Figure 10)], and to further reduce radiation and contrast dose for all CT imaging [63].…”