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The evaluation and diagnosis of thoracic aortic disease using magnetic resonance imaging, including magnetic resonance angiography, is assuming an increasing role in clinical practice. Comparison with other modalities, including computed tomography and echocardiography, is discussed. Newer magnetic resonance imaging techniques, including 3-D breath-hold time-of-flight sequences are highlighted, as well as imaging strategies using standard magnetic resonance imaging techniques. Thoracic aortic disease entities covered include aneurysm, dissection, penetrating ulcers and intramural hematoma, aortitis and infection, tumors, and congenital aortic disease.

OBJECTIVE Use of MRA for thoracic aortic disease (TAD) evaluation has been limited. This report describes an initial experience with TAD evaluation using a single MRA volume series. MATERIALS AND METHODS A single volume series, based on sequential 2D TOF MRA, was acquired in 30 cases (28 with suspected TAD and 2 normals). Each series was processed using multiplanar reconstruction (MPR) and maximum intensity projection (MIP); resulting tomographic (one base and two MPR) and MIP sets were blindly interpreted by four reviewers to detect TAD and, if present, to diagnose its specific form. For cases incorrectly interpreted, the standard MR images were subsequently interpreted. RESULTS The TAD categories included aneurysm (n = 13), dissection (n = 9), and arch anomalies (n = 5). Sensitivities were high for TAD overall (89-100%) and TAD in ascending and descending portions; sensitivities were lower for TAD of the arch (two of four reviewers > or = 90% for TAD overall and descending TAD). Specificities for TAD overall had a wider range (67-100%), but were high for ascending, arch, and descending portions (three to four of four reviewers > or = 90% for each). Sensitivities for aneurysms (69-92%) and dissections overall (67-100%) were comparable, as they were in ascending and arch portions; descending dissection was better detected than descending aneurysm (two of four reviewers > or = 90% for ascending or arch aneurysm and for descending dissection); overall specificities (88-100 vs. 81-95%) and specificities in ascending, arch, and descending portions were also comparable (three to four of four reviewers > or = 90% for both in each portion; two of four reviewers > or = 90% for dissection overall). Each reviewer achieved > or = 70% diagnostic accuracy for TAD (one of four reviewers = 85%); accuracies for each category were comparable. Interpretation of standard MR images corrected all detection and most diagnostic (> or = 63%) errors. CONCLUSION This initial experience with conventional TOF MRA for TAD evaluation is encouraging, but it indicates the potential for advancements in data acquisition and/or postprocessing.

Congenital variations in the development of the thoracic aorta are common. Although there is a spectrum of disease in all age groups, arch anomalies that present in childhood and those that present in the adult tend to be of differing types. Imaging of the arch and its branches, the descending aorta, and the ductus arteriosus or ligamentum arteriosum define the morphology of the arch and permit a reasonable prediction of accompanying congenital heart disease and/or vascular ring.

Three-dimensional (3D) volume turbo fast low angle shot (FLASH) techniques have become available which produce heavily T1-weighted images, similar to inversion recovery scans, utilizing the appropriate flip angle and inversion time. The purpose of this study was to compare the sensitivity of a rapid volume gradient echo technique [3D magnetization prepared rapid acquisition gradient echo (MP RAGE)] in identifying multiple sclerosis (MS) plaques with a conventional T2-weighted spin echo (SE) sequence. Ten patients with clinical MS were evaluated. Patients underwent a routine examination consisting of an axial T2-weighted SE sequence (2,500,22/90) and a coronal 3D MP RAGE, 10/4/10, acquired as 128 two mm partitions. In six patients, area measurements of 22 plaques were determined on both the axial T2-weighted SE examinations and the axial reformatted MP RAGE examinations. The overall number of plaques utilizing each technique was approximately the same. One hundred twenty-two plaques were visualized for the 3D MP RAGE sequence, and 128 plaques for the T2-weighted SE sequence. There were differences in detection of plaques in different regions, with plaques in gray matter better demonstrated utilizing the conventional T2-weighted SE sequence. Plaques in the corpus callosum, pons, and brachia pontis were better demonstrated utilizing 3D MP RAGE. No significant difference was found between the areas measured on the MP RAGE sequence and on the T2-weighted SE sequence. Three-dimensional MP RAGE provides a sensitive and complementary method to conventional T2-weighted SE sequences in the evaluation of patients with MS.

A three-dimensional (3D) fast imaging with steady state precession sequence structured to maintain constant phase at the radiofrequency pulse, in the presence of motion, was employed to produce high signal intensity of the CSF relative to the extradural and neural structures in 170 consecutive spine MR examinations. In addition to displaying the resulting partitions as two-dimensional (2D) images, the acquisition was subjected to a maximum intensity projection postprocessing algorithm for viewing at multiple angles. The projected images demonstrated a global view of the thecal sac and the dural root sleeves. The global depiction of the thecal sac and root sleeves was equivalent to contrast myelography in 15 patients where comparisons were available. These projection myelographic images, used in conjunction with 2D and reformatted 3D cross-sectional images, may provide clinical services with enough information (in a format with which they are comfortable) to eventually eliminate the need for contrast myelography in the evaluation of extradural disease.

DEGENERATION OF THE INTERVERTEBRAL disk is a ubiquitous process, seen at autopsy in 97% of adults by age 49 years (1). Low back pain is the most expensive health care problem in patients 20–50 years old, with $14 billion spent yearly on treatment and compensation (2). The greatest costs connected with low back pain occur in patients who have pain longer than 3 months and in those with recurrent pain episodes (3). Approximately 5.2 million people are disabled by back pain (3–5). These statistics indicate that the accurate diagnosis of back pain disease is obviously of great importance. In the diagnosis of disk degeneration and its sequelae, magnetic resonance (MR) imaging has become a key ingredient. The utility of conventional two-dimensional spin-echo MR imaging of the spine has been firmly established for extradural disease (6–8). Gradient-echo techniques have more recently been used to enhance the cerebrospinal fluid (CSF)-extradural interface in the evaluation of degenerative disease (9–13). Some of the new imaging findings and concepts regarding the use of contrast material and three-dimensional techniques in the evaluation of degenerative disease of the spine are reviewed.

To evaluate right ventricular abnormalities with magnetic resonance (MR) imaging in patients with arrhythmia but without arrhythmogenic dysplasia.In 53 patients being evaluated for right ventricular arrhythmia and 15 control subjects, MR imaging was performed to evaluate fixed thinning, fatty replacement, or reduced systolic wall thickening or motion. A diagnosis of idiopathic right ventricular outflow tract tachycardia or indeterminate was assigned for each patient, and the severity of arrhythmia was categorized.Right ventricular abnormalities were revealed in 32 (60%) of the 53 patients: fixed thinning in 27 (84%), fatty replacement in eight (25%), and reduced wall thickening or motion in 31 (97%). Right ventricular abnormalities were found in 35 (76%) of 46 patients with idiopathic right ventricular outflow tract tachycardia and in seven (39%) of 18 patients with indeterminate diagnoses (P = .022).Mild right ventricular abnormalities are likely sources for arrhythmias, even in the absence of arrhythmogenic right ventricular dysplasia.

To evaluate magnetic resonance (MR) imaging findings of intramural hematoma of the thoracic aorta and their relationship to prognosis.MR images of 22 patients with intramural hematoma of the thoracic aorta were reviewed retrospectively. Site, thickness, degree of mural involvement, and signal intensity on spin-echo (SE) and cine gradient-echo (GRE) images of the hematoma were noted. MR findings of patients who did and those who did not develop complications were compared.Hematoma site was the only MR finding that correlated significantly with patient outcome. Complication frequencies in four (80%) of five patients with hematoma of the ascending aorta (type A) and in two (12%) of 17 patients with hematoma of the descending aorta (type B) were significantly different (P = .009). There were moderately strong correlations between days after symptom onset and signal intensity of the hematoma on SE (r = 0.78) and GRE (r = 0.72) images. MR images of two of three patients who developed early-subacute complications showed signal intensity changes of the hematoma that were consistent with recurrent bleeding.Patients with MR findings consistent with type A intramural hematoma of the thoracic aorta should undergo surgery. In cases of type B intramural hematoma of the thoracic aorta, MR imaging can be useful for detecting complete resolution or impending complications of the hematoma.

To define the time course and mechanism of enhancement of epidural fibrosis after gadolinium-DTPA (Gd-DTPA) injection, we undertook a three-part study in humans and dogs with epidural scar after spine surgery. First, the dynamic in vivo contrast-enhancing properties of epidural scar were assessed by using sequential fast (18-sec) spin-echo sequences after contrast injection. Epidural scar in dogs rapidly enhanced; peak enhancement (101%) was 6 min after injection, with a slower decline toward baseline to 45% after 44 min. Epidural fibrosis in patients followed a similar pattern, with a maximum enhancement of 73% after 5 min. Paraspinal muscle had a lower peak enhancement in both patients (36%) and dogs (22%). Second, vascular injection in two dogs with India ink demonstrated multiple small vessels throughout the epidural scar. Third, light and electron microscopy was performed on epidural scar obtained at reoperation in both patients and dogs. Light microscopy showed multiple small capillaries scattered throughout a background of collagen. Electron microscopy demonstrated a wide variation in the junctions between endothelial cells ranging from "tight" to "loose." Regions of endothelial discontinuity were also visualized. This study suggests that Gd-DTPA diffuses rapidly into the extravascular space in epidural scar, with a slower, net movement toward the intravascular compartment as the agent is renally filtered. The contrast agent transgresses the endothelium through "leaky" intercellular junctions and areas of endothelial discontinuity.

A prospective study was undertaken on 204 consecutive patients comparing low flip angle gradient-echo and T1-weighted spin-echo techniques in the MR evaluation of cervical extradural disease. Four patient groups were studied with varying gradient-echo TEs (6 or 13 msec) and flip angles (10 degrees or 60 degrees). Images were evaluated independently for contrast behavior and anatomy, then directly compared for conspicuity of lesions. The FLASH sequences (especially with a 10 degrees flip angle) produced better conspicuity of disease in half the imaging time. T1-weighted spin-echo sequences were more sensitive to marrow changes and intradural disease. The short TE sequence (6 msec) did not produce any diagnostic advantage over the longer TE sequence (13 msec). A fast and sensitive MR examination for cervical extradural disease combines a sagittal T1-weighted spin-echo acquisition with sagittal and axial FLASH 10 degrees sequences.