Digital tomosynthesis is a novel technique that allows easy and swift volume data acquisition in selected regions of the body. However, many radiologists and technologists are unfamiliar with this technique and the potential artifacts related to data acquisition. Digital tomosynthesis requires a single linear sweep of the x-ray tube assembly with corresponding tomographic reconstruction of large-area flat-panel detector radiographic data. Standard acquisition parameters include sweep angle, sweep direction, patient barrier-object distance, number of projections, and total radiation dose. Potential acquisition-related artifacts include blurring-ripple, ghost artifact-distortion, poor spatial resolution, image noise, and metallic artifact. A comprehensive understanding of the relationships between acquisition parameters and potential associated artifacts is critical to optimizing acquisition technique and avoiding misinterpretation of artifacts. Sweep direction should be chosen on the basis of the anatomy of interest and the purpose of the examination so as to reduce the influence of blurring-ripple, ghost artifact-distortion, and metallic artifact. Adjusting the sweep angle, number of projections, and radiation dose will optimize depth resolution, avoid ripple in the sections of interest, and reduce unnecessary radiation exposure without compromising image quality. Thus, it is important that the radiologist and technologist establish appropriate protocols for different examination types to allow optimal utilization of this novel imaging technique.

Multidetector coronary computed tomography (CT), which is widely performed to assess coronary artery disease noninvasively and accurately, provides excellent image quality. Use of electrocardiography (ECG)-controlled tube current modulation and low tube voltage can reduce patient exposure to nephrotoxic contrast media and carcinogenic radiation when using standard coronary CT with a retrospective ECG-gated helical scan. Various imaging techniques are expected to overcome the limitations of standard coronary CT, which also include insufficient spatial and temporal resolution, beam-hardening artifacts, limited coronary plaque characterization, and an inability to allow functional assessment of coronary stenosis. Use of a step-and-shoot scan, iterative reconstruction, and a high-pitch dual-source helical scan can further reduce radiation dose. Dual-energy CT can improve contrast medium enhancement and reasonably reduce the contrast dose when combined with noise reduction with the use of iterative reconstruction. High-definition CT can improve spatial resolution and diagnostic evaluation of small or peripheral coronary vessels and coronary stents. Dual-source CT and a motion correction algorithm can improve temporal resolution and reduce coronary motion artifacts. Whole-heart coverage with 320-detector CT and an intelligent boundary registration algorithm can eliminate stair-step artifacts. By decreasing beam hardening and enabling material decomposition, dual-energy CT is expected to remove or reduce the depiction of coronary calcification to improve intraluminal evaluation of calcified vessels and to provide detailed analysis of coronary plaque components and accurate qualitative and quantitative assessment of myocardial perfusion. Fractional flow reserve derived from coronary CT is a state-of-the-art noninvasive technique for accurately identifying myocardial ischemia beyond coronary CT. Understanding these techniques is important to enhance the value of coronary CT for assessment of coronary artery disease.

Alongside the two conventional unenhanced magnetic resonance (MR) angiographic techniques, namely time-of-flight and phase-contrast MR angiography, several novel techniques have since been developed, including electrocardiograph (ECG)-gated fast spin echo (FSE), steady-state free precession (SSFP), and arterial spin labeling. These techniques are increasingly being used to avoid severe complications caused by contrast materials, such as iodinated contrast material-induced nephropathy and gadolinium-induced nephrogenic systemic fibrosis. However, image acquisition and interpretation with these techniques are more complicated than with contrast-enhanced MR angiography because of numerous types of artifacts. Appropriate use of these techniques can allow diagnosis of vascular diseases in patients with chronic kidney disease without using contrast materials. For example, time-of-flight angiography is the main technique for evaluating intracranial arteries. Phase-contrast imaging is increasingly being used for physiologic evaluation rather than morphologic evaluation. Meanwhile, ECG-gated FSE MR angiography can show peripheral arteries in more detail. SSFP MR angiography with or without arterial spin labeling can provide high-resolution images of blood vessels including renal arteries, the aorta, and coronary arteries. Black-blood imaging is also used to evaluate vessel walls and intravascular abnormalities including plaque, dissection, and thrombi. The authors review the principles of the currently available unenhanced MR angiographic techniques, along with their advantages and limitations, and describe their clinical applications. This article should help readers select the most appropriate unenhanced MR angiographic technique to assess vascular diseases in patients with chronic kidney disease. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.312105075/-/DC1.

Single-source dual-energy (DE) computed tomography (CT) with fast switching of tube voltage allows projection-based image reconstruction, substantial reduction of beam-hardening effects, reconstruction of accurate monochromatic images and material decomposition images (MDIs), and detailing of material composition by using x-ray spectral information. In vascular applications, DE CT is expected to overcome limitations of standard single-energy CT angiography, including patient exposure to nephrotoxic contrast medium and carcinogenic radiation, insufficient contrast vascular enhancement, interference from metallic and beam-hardening artifacts and severe vessel calcification, and limited tissue characterization and perfusion assessment. Acquisition of low-energy monochromatic images and iodine/water MDIs can reasonably reduce contrast agent dose and improve vessel enhancement. Acquisition of virtual noncontrast images, such as water/iodine MDIs, can reduce overall radiation exposure by replacing true noncontrast CT in each examination. Acquisition of monochromatic images by using metal artifact reduction software or acquisition of iodine/water MDIs can reduce metal artifacts with preserved or increased vessel contrast, and subtraction of monochromatic images between two energy levels can subtract coils composed of dense metallic materials. Acquisition of iodine/calcium (ie, hydroxyapatite) MDIs permits subtraction of vessel calcification and improves vessel lumen delineation. Sensitive detection of lipid-rich plaque can be achieved by using fat/water MDIs, the spectral Hounsfield unit curve (energy level vs CT attenuation), and a histogram of effective atomic numbers included in an image. Various MDIs are useful for accurate differentiation among materials with high attenuation values, including contrast medium, calcification, and fresh hematoma. Iodine/water MDIs are used to assess organ perfusion, such as in the lungs and myocardium. Understanding these DE CT techniques enhances the value of CT for vascular applications. (©)RSNA, 2016.

Purpose:To confirm the superiority of the navigator-triggered prospective acquisition correction (PACE) technique over the conventional respiratory-triggered (RESP) technique, something that has been perceived experimentally but without definite evidence, for free-breathing three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP) using healthy volunteers. Materials and Methods:Free-breathing 3D turbo spinecho MRCP using both PACE and RESP techniques were prospectively performed on 25 healthy volunteers. Quantitative analyses of acquisition time, signal-to-noise ratio, contrast-to-noise ratio, and contour sharpness index of each segment of the pancreaticobiliary tree were compared using the paired t-test. Qualitative analyses on a five-point scale (1, excellent; 5, poor) scored by two independent radiologists were compared using the Wilcoxon signed-rank test. Results:The subjective image quality and contour sharpness index of each segment of the PACE technique were found to be significantly better than those for RESP (P Ͻ 0.05). No significant difference was observed with regard to signal-to-noise and contrast-to-noise ratios except for the pancreatic duct. No significant difference in acquisition times between PACE and RESP techniques was observed. Conclusion:We confirmed the superiority of the image quality of the PACE technique compared to conventional RESP technique for free-breathing 3D MRCP in healthy volunteers.

The purpose of this clinical note is to describe the feasibility of using diffusion‐weighted imaging for diagnosing placental invasion with a case of placenta increta and six cases without it. Diffusion‐weighted imaging (DWI) at a b‐value of 1000 sec/mm2 can clearly define the border between the placenta and myometrium because only the placenta shows very high signal intensity. The corresponding image at a b‐value of 0 sec/mm2 shows the myometrium with high signal intensity compared with the surrounding fat. Therefore, fusion of the two images can be used additionally to visualize thickness of the myometrium. As a result, DWI can be used to visualize the focal thinning of the myometrium caused by placenta increta, which has been difficult to diagnose on conventional magnetic resonance imaging sequences without contrast enhancement. However, the use of DWI for placental invasion should be determined following careful consideration of its risks and benefits, as fetus safety has not been established. J. Magn. Reson. Imaging 2009;30:666–671. © 2009 Wiley‐Liss, Inc.

MCT has shown performance comparable to that of conventional FAC in terms of pancreatic and biliary depiction and safety.

Pseudoaneurysm of the cystic artery is rare; to our knowledge, fewer than 30 cases have been reported worldwide. We report the first case of an unruptured pseudoaneurysm of the cystic artery with concurrent acute calculous cholecystitis. We incidentally detected the aneurysm by contrast-enhanced computed tomography (CT) in the edematous, thickened wall of the gallbladder neck in a 71-year-old man, whereas in most of the reported cases the disease presented as hemobilia. Because of the high risk of aneurysm rupture in this location, we avoided such interventions as percutaneous cholecystostomy and laparoscopic cholecystectomy. The aneurysm was localized pathologically in the undisrupted gallbladder wall, and elective open cholecystectomy with ligation of the cystic artery was performed successfully. Our case highlights the usefulness of CT for both diagnosis and patient management. Open cholecystectomy with ligation of the cystic artery is demonstrated as a reasonable first line of treatment for this unusual condition.