The gastric air-fluid sign: aid in CT assessment of gastric wall thickening

The differentiation of apparent gastric wall thickening due to incomplete gastric distention from true pathologic wall thickening can be difficult on computed tomographic (CT) scanning. We have observed a transition in gastric wall thickening that is often present at or slightly above the gastric air-fluid or air-contrast level. The apparently thickened gastric wall in the dependent portion of the stomach undergoes an abrupt change to normal thickness at or above the air-fluid level. Review of CT scans in 259 patients without known or suspected gastric pathologic conditions revealed this finding, termed the "gastric air-fluid sign," in 57 patients (22%). While not considered diagnostic, the presence of this sign may allow for a greater degree of confidence in the CT assessment of gastric wall thickening in an appropriate clinical setting.     

MR imaging artifacts. Challenges and solutions

A wide variety of artifacts is routinely encountered on MR images. This article reviews the cause, appearance, diagnostic effect, and available remedies for the artifacts that are most frequently observed on MR images and are of greatest clinical significance. Combined with routine preventive maintenance of imaging equipment, consistent quality control, and appropriate selection of imaging parameters, awareness of the manifestations of these artifacts will allow image quality and diagnostic interpretation to be optimized.     

Normal rotator cuff: MR imaging with conventional and fat-suppression techniques

The signal intensity and morphologic characteristics of the rotator cuff and surrounding structures at magnetic resonance (MR) imaging were investigated with five pulse sequences in 15 asymptomatic subjects. In all subjects, a focal region of relative increased signal intensity corresponding to the critical zone was observed in the supraspinatus tendon just proximal to its insertion. Soft-tissue signal intensity (isointense with muscle) was also located between the supraspinatus tendon and underlying joint capsule, interposed between the conjoined leaves of the supraspinatus and infraspinatus tendons, and superolateral to the conjoined cuff tendon, near its insertion. These regions were most conspicuous and most clearly defined with fat-suppression imaging. Small amounts of fluid were observed within the joint space and its recesses, the bicipital tendon sheath, and the subacromial-subdeltoid bursa. These and other MR imaging findings of this study previously have been regarded as indicative of rotator cuff abnormalities. These results will help refine the criteria for diagnosis of rotator cuff disorders with MR imaging.     

Interactive multiplanar reformation of conventional two-dimensional MR images

In this report, we describe a new application for three-dimensional computer image processing that can provide for improved depiction of anatomical structures on routine nonvolumetric magnetic resonance (MR) examinations. The technique can be applied to standard two-dimensional MR images of the brain, spine, musculoskeletal system, and body including those obtained with relatively thick slices and with an intersection gap. This report demonstrates use of the reformation technique to establish retrospectively the symmetry in bilateral structures that were displayed out of alignment due to suboptimal patient positioning or patient motion during image acquisition and to improve the depiction of anatomical structures that were oriented out of the plane of original image acquisition. This method can be performed interactively in near real time, requires no increase in patient examination time, and has potential application throughout the body.     

Magnetic resonance imaging of congenital heart disease

MRI has assumed an important role in the noninvasive evaluation of patients with congenital cardiac lesions. In this article, the authors examine basic technical considerations, an approach to analysis of MR images in congenital heart disease patients, and review major applications of MRI as they apply to patients with congenital heart disease.     

Perfluoroctylbromide as a gastrointestinal contrast agent for MR imaging: use with and without glucagon

The utility of perfluoroctylbromide (PFOB) as a gastrointestinal contrast agent for magnetic resonance (MR) imaging was evaluated with MR examinations performed in 30 subjects (16 healthy volunteers and 14 patients). Transaxial T1-, proton density-, and T2-weighted MR images were acquired in each subject before and after the administration of PFOB. The healthy volunteers each underwent two sets of post-PFOB MR examinations, one before and one after glucagon administration. The degree of bowel marking, clarity of bowel-wall visualization, ability to distinguish bowel from adjacent parenchymal organs, and severity of phase-encoding artifacts were independently analyzed by two reviewers. Oral administration of PFOB significantly (P less than .001) increased the percentage of bowel loops with low signal intensity. Subcutaneous administration of glucagon significantly (P less than .001) increased the clarity of bowel-wall visualization on post-PFOB MR studies. The severity of phase-encoding artifacts did not change substantially after administration of PFOB or glucagon.     

MR imaging evaluation of knee collateral ligaments and related injuries: Comparison of T1-weighted,T2-weighted,and fat-saturated T2-weighted sequences—correlation with clinical findings

The objectives of this study were to compare the ability of T1-weighted (T1W), proton density/T2-weighted (PD/T2W), and fat saturation (FS) PD/T2W magnetic resonance (MR) sequences for depiction of the knee collateral ligaments and related injuries, and to compare MR findings with clinical findings. Ten subjects with normal knee ligaments and 64 patients with suspected collateral ligament injuries underwent coronal T1W, PD/T2W, and FS PD/T2W imaging. Abnormalities ranged from edema surrounding the collateral ligaments (grade I) to complete disruption of ligamentous fibers (grade III). FS PD/T2W images improved definition of the medial collateral ligament (MCL) and lateral collateral ligament (LCL) compared with other sequences in 78% and 81% of patients, respectively. While the apparent grade of collateral ligament injury was similar with all pulse sequences in most patients, depiction of such injury was usually most conspicuous on FS PD/T2W images (MCL, 92% of patients; LCL, 38% of patients). In no patients were clinically diagnosed collateral ligament injuries undetected or understaged with MR imaging. MR findings indicated higher-grade MCL and LCL injuries than did clinical examination in 24 and 15 patients, respectively.     

Tetralogy of Fallot: MR findings

Surgical treatment of patients with tetralogy of Fallot requires accurate definition of all anatomic structures, particularly the central pulmonary arteries. Magnetic resonance (MR) images of 22 patients with tetralogy of Fallot were studied to assess their usefulness in providing information regarding the spectrum of anatomic abnormalities in this condition. MR findings were compared with information obtained at catheterization (in 16 patients) and at surgery (in nine patients), both of which were performed within 3 months of MR imaging. Ventricular chamber enlargement and wall hypertrophy were clearly delineated in most of the 17 patients who were examined before definitive surgical repair, and ventricular septal defects were visualized in all 17. Palliative systemic-to-pulmonary shunts were visualized in 11 patients and could be evaluated for patency. Most important, the morphology and size of the right ventricular outflow tract and central pulmonary arteries could be accurately assessed. Pulmonary artery measurements obtained from MR images demonstrated excellent correlation with angiographic measurements. In six patients examined after complete surgical repair, MR images accurately reflected changes in pulmonary artery outflow tract morphology and complications, such as residual pulmonary artery stenosis and thrombosis. The findings suggest that MR imaging can complement or obviate catheterization in the evaluation of tetralogy of Fallot with regard to suitability for definitive surgical repair.     

Ulnar collateral ligament injury in baseball pitchers: MR imaging evaluation.

The ulnar collateral ligament (UCL) provides stability to the medial aspect of the elbow during valgus stress. Trauma to this ligament may result from repetitive forceful throwing. Diagnosis of UCL injury has been based on clinical findings of medial joint pain and valgus instability, as direct imaging of this structure has not been available. Eleven baseball pitchers with clinical evidence of UCL injury were evaluated with magnetic resonance (MR) imaging. Surgical correlation was obtained in six patients, four of whom underwent UCL reconstruction. MR imaging findings in UCL injury included laxity, irregularity, poor definition, and increased signal intensity within and adjacent to the UCL. These findings reflect the presence of hemorrhage and/or edema within the UCL due to repeated microtears, which eventually lead to weakening and possible disruption of the UCL. Optimization of spatial resolution, signal-to-noise ratio, and other technical factors is critical for evaluation of the UCL due to its small size. MR imaging is useful in documenting the presence and severity of injury to the UCL and in distinguishing this entity from other causes of elbow pain.     

Evaluation of pulmonary arterial morphology in cyanotic congenital heart disease by magnetic resonance imaging

Before and after surgical therapy, the anatomy of the pulmonary arteries in cyanotic congenital heart disease is often distorted. Pulmonary arterial anatomy was evaluated by magnetic resonance imaging (MRI) and angiography in 20 patients, ages 3 months to 20 years, with cyanotic heart disease associated with decreased pulmonary blood flow. Excellent correlation between MRI and angiographic estimates of pulmonary artery diameter was obtained (main pulmonary artery, r = 0.96; right pulmonary artery, r = 0.93; left pulmonary artery, r = 0.96). A similar excellent correlation (kappa = 0.83) was found in the assessment of the presence and severity of proximal pulmonary arterial stenoses. However, stenoses in the peripheral pulmonary arteries visualized with angiography were missed with MRI. MRI and angiography showed complete agreement in determining the patency of 11 surgical shunts. MRI did not demonstrate all of the systemic collateral vessels present with angiography, and the distal connections of collaterals were not detected with MRI. MRI is comparable to angiography in the evaluation of central pulmonary arterial anatomy over a wide range of ages. These findings suggest an important role for noninvasive MRI in the serial evaluation of pulmonary artery morphology in patients with cyanotic congenital heart disease before and after surgical repair.