Dual-energy liver CT: effect of monochromatic imaging on lesion detection, conspicuity, and contrast-to-noise ratio of hypervascular lesions on late arterial phase.

OBJECTIVE: The purpose of this study was to evaluate the effect of use of dual-energy CT monochromatic imaging in the late hepatic arterial phase on hyperenhancing focal lesion detection and lesion conspicuity. SUBJECTS AND METHODS: This prospective study included 72 patients imaged with a single-source dual-energy CT scanner. Late arterial phase imaging was performed with dual energies of 140 and 80 kVp, and the portal venous and delayed phases were performed with a single energy of 120 kVp. Two deidentified image sets were created: set A consisted of 77-keV images only, and set B consisted of 40-, 50-, 70-, and 77-keV images and iodine-based contrast material decomposition images. Two independent reviewers identified hypervascular lesions and subjectively scored lesion conspicuity. Contrast-to-noise ratios were calculated, and radiation dose (volume CT dose index) was recorded. RESULTS: The 128 lesions identified had a mean size of 1.7 ± 1.4 cm. There was no difference in lesion detection between the two reviewers or the two image sets. The contrast-to-noise ratio at 50 keV was 72% greater than that at 77 keV (p < 0.0001). Subjective conspicuity was statistically greatest at 50 keV (p < 0.0001). There was no statistical difference in mean volume CT dose index between the dual-energy (12.8 mGy) and the two single-energy (14.4 and 14.2 mGy) phases. CONCLUSION: Viewing dual-energy CT images may result in the greatest subjective lesion conspicuity and measured contrast-to-noise ratio at 50 keV with equal detection of hyperenhancing liver lesions compared with viewing 77-keV images alone. In addition, the radiation doses of dual-energy CT may be similar to those of single-energy CT.

Ferumoxytol in clinical practice: implications for MRI.

Ferumoxytol is an iron-containing parenteral treatment for iron deficiency anemia that was recently approved by the Food and Drug Administration. The iron is in the form of a superparamagnetic iron oxide that causes T1, T2, and T2* shortening on magnetic resonance imaging (MRI). Furthermore, the drug has a long intravascular half-life of 14-15 hours; a standard dose can affect MRI for days to months. We describe a case in which a patient underwent contrast-enhanced MRI of the liver 2 days after receiving a dose of ferumoxytol, which was unknown to the radiology team. The blood pool and soft tissues were hyperintense on T1-weighted images, concealing enhancement from the gadolinium-based contrast agent that was administered during the exam and rendering the exam nondiagnostic. Radiologists must be aware of this potential effect in screening patients for MRI and interpreting exams.

Noncontrast functional MRI of the kidneys.

Functional magnetic resonance imaging (fMRI) techniques enable noninvasive assessment of renal function. Diffusion-weighted imaging, diffusion tensor imaging, blood oxygen level-dependent MRI, magnetic resonance elastography, and arterial spin labeling are some of the emerging techniques that have potential to investigate renal function without the use of exogenous gadolinium contrast. This article discusses the principles of these techniques, as well as their possible applications and limitations. This will introduce the readers to these novel imaging tools, which appear to have promising futures.

Prospectively ECG gated CT pulmonary angiography versus helical ungated CT pulmonary angiography: impact on cardiac related motion artifacts and patient radiation dose.

OBJECTIVE: To compare prospectively ECG gated CT pulmonary angiography (CTPA) with routine helical ungated CTPA for cardiac related motion artifacts and patient radiation dose. SUBJECTS AND METHODS: Twenty patients with signs and symptoms suspicious for pulmonary embolism and who had a heart rate below 85 were scanned with prospectively ECG gated CTPA. These gated exams were matched for several clinical parameters to exams from twenty similar clinical patients scanned with routine ungated helical CTPA. Three blinded independent reviewers subjectively evaluated all exams for overall pulmonary artery enhancement and for several cardiac motion related artifacts, including vessel blurring, intravascular shading, and double line. Reviewers also measured pulmonary artery intravascular density and image noise. Patient radiation dose for each technique was compared. Fourteen clinical prospectively ECG gated CTPA exams from a second institution were evaluated for the same parameters. RESULTS: Prospectively ECG gated CTPA resulted in significantly decreased motion-related image artifact scores in lung segments adjacent to the heart compared to ungated CTPA. Measured image noise was not significantly different between the two types of CTPA exams. Effective dose was 28% less for prospectively ECG gated CTPA (4.9 mSv versus 6.8 mSv, p=0.02). Similar results were found in the prospectively ECG gated exams from the second institution. CONCLUSION: Compared to routine helical ungated CTPA, prospectively ECG gated CTPA may result in less cardiac related motion artifact in lung segments adjacent to the heart and significantly less patient radiation dose.

Negative ECG-gated cardiac CT in patients with low-to-moderate risk chest pain in the emergency department: 1-year follow-up.

OBJECTIVE: The purpose of this article is to determine the frequency of adverse cardiac events during the year following a negative cardiac CT angiogram in a population of patients presenting to the emergency department with low-to-moderate risk chest pain. SUBJECTS AND METHODS: Eighty-one consecutive patients who had standard of care evaluation for low-to-moderate risk chest pain in the emergency department were enrolled and consented to have a cardiac CT angiogram added to their workup and to have follow-up for 1 year. Eleven patients were excluded, six because their cardiac CT examinations were unsuccessful, four because of a positive cardiac CT angiogram result, and one was lost to follow-up. Seventy patients with negative cardiac CT angiographic results (< 50% stenosis) were included and were interviewed in detail at 3, 6, and 12 months about intervening cardiac events, diagnostic testing, and therapy. Electronic medical records were also reviewed at each time point. RESULTS: None of the 70 patients reported an adverse cardiac event over the 12-month follow-up period. At 1 year, the cause of chest pain was unknown in 49 patients, gastrointestinal in nine patients, anxiety in seven patients, musculoskeletal in three patients, and other in two patients. Three of four patients with 50% or greater stenosis on their cardiac CT had subsequent cardiac catheterization and stent placement. CONCLUSION: In patients with low-to-moderate risk chest pain evaluated in the emergency department, adverse cardiac events may be rare during the 12 months following a negative cardiac CT angiogram.

The management of indeterminate incidental findings detected at abdominal CT.

Abdominal computed tomography (CT) scans often have findings that are incidental to the reason the study was ordered. Several recent studies and reviews have addressed how these findings should be managed. This article summarizes current management strategies for several types of lesions that are commonly encountered. Some of these findings can be characterized without additional imaging (including simple renal cyst, angiomyolipoma, hepatic steatosis). Other findings are indeterminate. While some of these indeterminate incidental findings can be ignored based on statistical arguments (for example, a sharply circumscribed homogeneous low-attenuation renal lesion under 1 cm in patients without a predisposition to develop renal cell carcinoma), many may need additional imaging studies to either characterize them or demonstrate stability over time. Adhering to these strategies will hopefully reduce overutilization of imaging services while directing attention to those findings which need diagnostic or therapeutic interventions.