Ann C. Price

The use of GD DTPA as a perfusion agent and marker of blood-brain barrier disruption

To provide contrast enhancement in magnetic resonance imaging, a new class of compounds has been developed, the paramagnetic metal ion chelates. Gadolinium (Gd) DTPA, a prototype of this class, shows a sufficiently high in vivo stability and low toxicity for use in initial clinical trials. This type of agent, designed for rapid clearance by glomerular filtration, allows the assessment on MRI of renal function, alterations in tissue perfusion, myocardial ischemia, and perhaps most significantly disruption of the blood-brain barrier (BBB). Research at Vanderbilt has demonstrated these applications, with particular emphasis in three areas. Tissue perfusion changes, such as those produced by ligation of the arterial blood supply to portions of the spleen and kidney, cannot easily be detected on unenhanced MRI. These acute tissue infarcts can be readily identified following the administration of Gd DTPA. The question of field strength dependence of Gd DTPA has been addressed by experimentation at 0.15, 0.5, and 1.5 tesla. Furthermore, the ability to detect an alteration of the BBB, when present without associated edema, has been demonstrated with the application of control enhancement. The use of contrast agents in MRI will enhance both the sensitivity and specificity of magnetic resonance imaging.

Contrast enhanced MRI. Evaluation of a canine model of osmotic blood-brain barrier disruption.

An osmotic model of blood-brain barrier (BBB) disruption was studied by magnetic resonance (MR) imaging (0.5 T) in 17 canines. The animals were killed after imaging and the lesions confirmed on gross pathology by the presence of Evans blue dye. No accompanying cerebral edema was demonstrated on histologic examination. The disrupted BBB could be identified in only one of five control animals on unenhanced MRI, despite the use of calculated T1 and T2 images. In a second group of five animals, the area of abnormal vascular permeability was consistently demonstrated after IV injection of 0.25 mmol/kg Gd DTPA. The time course of enhancement was evaluated in four additional animals. The brain tissue concentration of the gadolinium ion responsible for the observed enhancement was determined by ion coupled plasma analysis in the last three canines. In a study of pulse techniques, spin echo sequences with both short TRs and TEs (ie, SE 500/30) and inversion recovery techniques proved to be most efficacious for the detection of contrast enhancement. However, contrast could be demonstrated on more T2 weighted sequences.

Craniopharyngioma: CT and MR imaging in nine cases.

Magnetic resonance (MR) imaging and CT examinations were performed in nine patients with surgically proven craniopharyngioma. Computed tomography was found to be superior to MR in detection of calcification and cyst formation. Extent of involvement of adjacent structures (e.g., optic chiasm, third ventricle, and intracavernous carotid artery) was more clearly delineated by MR. Craniopharyngioma fluid collections were found to be uniformly bright on T2-weighted sequences. However, on T1-weighted sequences, the signal intensity of the fluid ranged from hypointense to hyperintense, reflecting the heterogeneous contents of cysts in these tumors. Since calcification and cyst formation are hallmarks of craniopharyngiomas, we believe that CT is more specific than MR in diagnosis of craniopharyngiomas. Magnetic resonance, however, offers a more accurate assessment of the tumor extent.

Primary glioma: diagnosis with magnetic resonance imaging

Seventeen patients with surgically documented primary glial-origin brain tumors were evaluated by magnetic resonance imaging and high-resolution computed tomography. The exclusion of CT ring-enhancing lesions directed the focus of this study toward lower grade tumors that were more difficult to diagnose. The computed tomography abnormalities were often subtle and included areas of low attenuation, mass effect, and focal enhancement. Spin-echo sequences with both heavy T1 and T2 weighting were utilized. Prolonged T1 and T2 values were observed in all tumors. The T2-weighted spin-echo 1000/120 sequence was the most sensitive in tumor detection and was positive in all cases. Magnetic resonance imaging was superior to computed tomography in tumor detection, tumor localization, assessment of tumor extent, and determination of associated changes, ie, brain stem encroachment. All the magnetic resonance sequences used showed an increase in severity of imaging changes with increasing tumor grade. The T2-weighted sequence showed progressive margin irregularity, whereas the T1-weighted (inversion recovery) sequence showed increasing severity of internal tissue changes. The superior resolution of these changes by magnetic resonance imaging may have implications for better assessment of tumor grade in the future than is currently possible with computed tomography.

Diagnosis of spinal arteriovenous malformation in a pregnant patient by MR imaging.

An intraspinal arteriovenous malformation (AVM) was diagnosed by magnetic resonance imaging in a pregnant patient. Serpentine areas of low signal intensity surrounded by cerebrospinal fluid were considered diagnostic of this surgically verified abnormality. In addition, T2 weighted images helped to determine the extent of the spinal canal occupied by the AVM.