Determination of blood flow direction using velocity-phase image display with 3-D phase-contrast MR angiography.

The authors describe their use of phase-contrast MRA to depict vascular anatomy and to define the direction of blood flow. Documentation of flow reversal can provide information regarding prognosis and can facilitate surgical planning. The technique requires no additional scan-time.

High-b-value diffusion-weighted MR imaging of adult brain: image contrast and apparent diffusion coefficient map features.

BACKGROUND AND PURPOSE: Recent improvements in MR gradient technology allow significant increases in diffusion weighting without prohibitive signal-to-noise degradation. The purpose of our investigation was to establish normative references for the signal intensity characteristics and apparent diffusion coefficient values of the adult brain at high b values. METHODS: Fifty adults underwent diffusion-weighted single-shot spin-echo echo-planar MR imaging. Isotropic diffusion-weighted images were obtained with b values of 0, 1,000, 2,000, 2,500, 3,000, and 3,500 s/mm2. Qualitative assessments were made in multiple regions of interest in gray and white matter. Three apparent diffusion coefficient maps were generated for each of six patients with a 2-point technique at a b value of 0 and at b values of 1,000, 2,000, and 3,000 s/mm2. RESULTS: Increasing b values result in a progressive decrease in the gray to white matter signal intensity ratio. Isointensity between gray and white matter results at b values between 1,000 and 2,000 s/mm2. At b values greater than 2,000, the gray-white pattern reverses relative to the usual b value of 1,000. Apparent diffusion coefficient values were shown to decrease with increasing b values. CONCLUSION: Attention to the reversal of gray-white contrast and the dependence of apparent diffusion coefficient on the b value are important in avoiding erroneous assignment of pathologic abnormalities to normal regions. This study provides the normative data for future diffusion investigations performed at high b values.

Three-dimensional phase-contrast MR angiography in the head and neck: preliminary report.

Morbidity and possible mortality associated with contrast angiography lead to its cautious use. A noninvasive method for screening and further delineating known abnormalities would be welcomed. This article reviews the initial results and application of MR imaging to vascular imaging in the head and neck. By using the three-dimensional phase-sensitive method of Dumoulin, Souza, and collaborators, we acquired MR angiograms in 37 min and portrayed blood flow in all the major arteries and veins. Feeding arteries and draining veins of arteriovenous malformations were well delineated; aneurysms as small as 3-4 mm were shown, and obstructed cerebral vessels and the patency of a highly stenotic internal carotid artery were demonstrated. MR angiography of the head or neck offers great promise as a noninvasive means of studying vascular abnormalities.

Physical principles and application of magnetic resonance angiography.

This paper reviews the physical principles of magnetic resonance angiography (MRA) acquisition methods, explains image presentation strategies for MRA, and discusses the advantages and disadvantages of various MRA methods. These methods include the time-of-flight, phase contrast, and black blood techniques. The essential goal of each of these flow imaging methods is to maximize signal differences between flowing and stationary tissues in order to provide morphological and physiological information.

Magnetic resonance angiography in intracranial vascular disease.

Magnetic resonance angiography (MRA) offers a noninvasive alternative for studying normal and pathological blood vessels within the brain. Insights from important clinical aspects of intracranial vascular disease enable the effective application of MRA. Several MRA techniques have demonstrated clinical utility for the detection and characterization of intracranial vascular pathology. Clinical protocols should comprise combinations of time-of-flight and phase-contrast acquisitions to achieve diagnostic sensitivity.

Acute brain MRI findings in 120 Malawian children with cerebral malaria: new insights into an ancient disease.

BACKGROUND AND PURPOSE: There have been few neuroimaging studies of pediatric CM, a common often fatal tropical condition. We undertook a prospective study of pediatric CM to better characterize the MRI features of this syndrome, comparing findings in children meeting a stringent definition of CM with those in a control group who were infected with malaria but who were likely to have a nonmalarial cause of coma. MATERIALS AND METHODS: Consecutive children admitted with traditionally defined CM (parasitemia, coma, and no other coma etiology evident) were eligible for this study. The presence or absence of malaria retinopathy was determined. MRI findings in children with ret+ CM (patients) were compared with those with ret- CM (controls). Two radiologists blinded to retinopathy status jointly developed a scoring procedure for image interpretation and provided independent reviews. MRI findings were compared between patients with and without retinopathy, to assess the specificity of changes for patients with very strictly defined CM. RESULTS: Of 152 children with clinically defined CM, 120 were ret+, and 32 were ret-. Abnormalities much more common in the patients with ret+ CM were markedly increased brain volume; abnormal T2 signal intensity; and DWI abnormalities in the cortical, deep gray, and white matter structures. Focal abnormalities rarely respected arterial vascular distributions. Most of the findings in the more clinically heterogeneous ret- group were normal, and none of the abnormalities noted were more prevalent in controls. CONCLUSIONS: Distinctive MRI findings present in patients meeting a stringent definition of CM may offer insights into disease pathogenesis and treatment.

Demonstration of an early draining vein by MR angiography.

We present a case of an arteriovenous malformation (AVM) where standard MR angiography demonstrated an enlarged basal vein of Rosenthal. The lenticulostriate branches of the middle cerebral artery were suggested but not conclusively shown, as the feeders of the AVM. Therefore, it could not be determined whether the enlarged vein was part of an AVM or of a venous angioma. By using a saturation pulse inferior to the image volume including the basal vein of Rosenthal and the middle cerebral artery, the transmission of "black blood" to the basal vein of Rosenthal was demonstrated. This implied early venous draining, which confirmed that the lesion represented an AVM.

Three-dimensional phase-contrast MR angiography in the head and neck: preliminary report.

Morbidity and possible mortality associated with contrast angiography lead to its cautious use. A noninvasive method for screening and further delineating known abnormalities would be welcomed. This article reviews the initial results and application of MR imaging to vascular imaging in the head and neck. By using the three-dimensional phase-sensitive method of Dumoulin, Souza, and collaborators, we acquired MR angiograms in 37 min and portrayed blood flow in all the major arteries and veins. Feeding arteries and draining veins of arteriovenous malformations were well delineated; aneurysms as small as 3-4 mm were shown, and obstructed cerebral vessels and the patency of a highly stenotic internal carotid artery were demonstrated. MR angiography of the head or neck offers great promise as a noninvasive means of studying vascular abnormalities.

Measuring performance in chest radiography.

PURPOSE: To use a standardized set of chest radiographs to quantify interobserver differences and to provide a basis for comparing the diagnostic performance of physicians. MATERIALS AND METHODS: A standardized set of 60 chest radiographs was presented to 162 study participants. Each participant reviewed the radiographs and recorded his or her diagnostic impression by using a fixed five-point scale. These response data were used to generate receiver operating characteristic curves and to establish performance benchmarks. The variations in performance were tested for statistical significance. RESULTS: Significant interobserver variability was identified during these assessments. The composite group of board-certified radiologists demonstrated performance superior to that of the radiology residents and nonradiologist physicians. CONCLUSION: By using a receiver operating characteristic approach and a standardized set of chest radiographs, observer accuracy and variability are easily quantified. This approach provides a basis for comparing the diagnostic performance of physicians. When value is measured as a diminution in uncertainty, board-certified radiologists contribute substantial value to the diagnostic imaging system.