Characterizing the mesencephalon using susceptibility-weighted imaging.

BACKGROUND AND PURPOSE: The mesencephalon is involved in a number of human neurodegenerative disorders and has been typically imaged with T1-, T2- and T2*-weighted methods. Our aim was to collect high-contrast susceptibility-weighted imaging (SWI) data to differentiate among and within the basic mesencephalic structures: namely, the red nucleus, substantia nigra, and crus cerebri. MATERIALS AND METHODS: High-resolution SWI, 3D T1-weighted, and T2-weighted data were collected to study contrast in the mesencephalon at 1.5T and 4T. Contrast between structures was calculated for SWI high-pass (HP)-filtered-phase, T1 gradient-echo, and spin-echo T2-weighted data. RESULTS: SWI HP-filtered-phase data revealed similar contrast for the red nucleus and substantia nigra when compared with T2-weighted imaging. However, SWI was able to show structures within the red nucleus, substantia nigra, and medial geniculate body that were invisible on T2-weighted imaging. T1-weighted imaging, on the other hand, did not reveal measurable contrast for any of the structures of interest. SWI HP-filtered-phase data at 4T agreed well with india ink-stained cadaver brain studies, which appear to correlate with capillary density. CONCLUSIONS: With SWI, it is possible to create better anatomic images of the mesencephalon, with improved contrast compared with conventional T1- or T2-weighted sequences.

High-resolution blood oxygen-level dependent MR venography (HRBV): a new technique.

Our purpose of this study was to demonstrate the clinical potential and spatial resolution of a new MRI technique: high-resolution blood oxygen-level dependent venography (HRBV), in well-known intracranial vascular lesions, such as cavernous and venous angiomas, and venous sinus thrombosis. HRBV provides unique high-resolution information on veins without administration of contrast medium. The data are independent of conventional findings on MRI and potentially useful in characterising and demonstrating the architecture of vascular lesions of the brain.

Evaluation of a reduced MR imaging sequencing protocol in adult patients with stroke.

PURPOSE: To compare a reduced (three-sequence) magnetic resonance (MR) imaging protocol with a full (eight- to 10-sequence) MR imaging protocol in adults suspected of having stroke. MATERIALS AND METHODS: Six neuroradiologists interpreted a consecutive sample of 265 MR images in patients suspected of having stroke. Each read reduced-protocol images in a discrete series of 40 patients (one read images in only 15) and corresponding full-protocol images 1 month later (reduced/full protocol). Five of the readers each read images in 10 additional cases, five each as full/full and reduced/reduced protocol controls. kappa values between full and reduced protocols, reader assessment of protocol adequacy, confidence level, and need for additional sequences or examinations were evaluated. RESULTS: In the reduced/full protocol, the kappa value for detecting ischemia was 0.797; and that for detecting any clinically important abnormality, 0.635. Statistically similar kappa values were found with the full/full control design (kappa = 0.802 and 0.715, respectively). The full protocol was judged more adequate than the reduced protocol (2.0 of 5.0 points vs 1.6, P <.001) and generated greater diagnostic confidence (8.6 of 10.0 points vs 8.9, P =.01), less need for additional sequences (2.7 of 6.0 points vs 1.5, P <.001), and more requests for additional examinations (28.4% vs 36.3%). CONCLUSION: Disagreement between interpretations of reduced- and full-protocol images might be attributable to baseline-level intraobserver inconsistency, as demonstrated in control designs. A greater number of sequences did not lead to greater consistency.

Comparison of CT myelography performed in the prone and supine positions in the detection of cervical spinal stenosis.

AIM: To quantify the change in the cross-sectional area of the cervical spinal cord and subarachnoid space (SAS) in the supine neutral vs prone extension positions in patients with myelopathy undergoing cervical CT myelography. MATERIAL AND METHODS: Axial CT myelgrams of 21 myelopathic patients were performed in both the supine neutral and prone extension positions. The SAS and cord cross-sectional areas were then measured at the disk spaces and mid-pedicle levels from C2 to T1 in both the supine and prone positions using a public domain NIH Image program, version 156b18. Mean area measurements in both positions were then compared for each level examined. RESULTS: Mean SAS cross-sectional area in the prone position was notably reduced compared with the supine position at C4-C5 [128.8 mm2 vs 168.1 mm2 (P<.05)], and C5-C6 [98.8 mm2 vs 143.2 mm2 (P<.05)] disk levels. The mean cord cross-sectional area failed to change significantly with positioning. CONCLUSIONS: Prone myelography may demonstrate a greater degree of cervical spine stenosis compared with CT myelography performed in the supine position in myelopathic patients. Imaging with the patient prone with neck extended in both myelography and CTM may improve precision in the results of measurements of the stenotic spinal canal when comparing these two methods. Blease Graham III, C. (2001). Clinical Radiology56, 35-39.

MR high-resolution blood oxygenation level-dependent venography of occult (low-flow) vascular lesions.

A new technique for detecting vascular malformations, high-resolution BOLD venography (HRBV), is described. This technique relies on the BOLD principle for detecting deoxygenated blood in low-flow malformations. HRBV images are acquired using a modified 3D gradient-echo with voxel volumes of 0.5 x 0.5 x 2 mm3. The magnitude data are masked with the phase images to enhance visibility of the venous structures and are displayed using the minimum intensity projection. Preliminary results for 10 patients show that HRBV is more sensitive in detecting cavernomas than is T2-weighted imaging, and lesions that are presumed to be telangiectasias are detected only with this technique.

Increased-contrast, high-spatial-resolution, diffusion-weighted, spin-echo, echo-planar imaging.

An insertable head gradient coil with a maximum gradient amplitude of 45 mT/m and a rise time of 150 musec along all three major axes was used to collect high-spatial-resolution, single-shot, spin-echo, echo-planar, diffusion-weighted magnetic resonance images with b values ranging from 0 to 2,200 sec/mm2. Improvements in spatial resolution allowed better visualization of large white matter tracts and their relation to adjacent anatomic structures. Excellent contrast and anatomic detail were revealed for most structures in the brain when a sufficient number of acquisitions were collected.

Brain magnetic resonance diffusion abnormalities in Creutzfeldt-Jakob disease.

BACKGROUND: Magnetic resonance imaging of the brain has been of limited usefulness in the diagnosis of Creutzfeldt-Jakob disease. Abnormalities on T2-weighted images have been described, but these are neither highly sensitive nor specific. OBJECTIVE: To determine whether diffusion-weighted magnetic resonance images might be useful in the evaluation of Creutzfeldt-Jakob disease. CASE PRESENTATION: A 61-year-old woman with rapidly progressive dementia was referred for cranial magnetic resonance imaging. Diffusion-weighted images were obtained as part of the examination. Brain biopsy confirmed the diagnosis of Creutzfeldt-Jakob disease histologically. FINDINGS AND CONCLUSIONS: The diffusion-weighted magnetic resonance brain images demonstrated bilaterally symmetrical marked increase in signal intensity in the caudate nuclei, putamina, thalami, cingulate gyri, and right inferior frontal cortex. The apparent diffusion coefficient map showed abnormally low diffusion in these regions (as low as 40% of normal in the caudate head). This suggests that there is restricted diffusion in these regions. The T2-weighted images demonstrated slightly increased signal bilaterally in the caudate nuclei and putamina. These findings indicate that diffusion magnetic resonance imaging might be a sensitive means of imaging the abnormalities seen in Creutzfeldt-Jakob disease.

Small vessels in the human brain: MR venography with deoxyhemoglobin as an intrinsic contrast agent.

To assess a magnetic resonance (MR) imaging method for depicting small veins in the brain, a three-dimensional, long echo time, gradient-echo sequence that depended on the paramagnetic property of deoxyhemoglobin was used. Veins with diameters smaller than a pixel were depicted. This MR imaging method is easy to implement and may prove helpful in the evaluation of venous diseases.

Hippocampal pathology.

Medial temporal sclerosis of the hippocampus and other lesions in the adjacent temporal lobe that can cause epilepsy are discussed in this article. The technical factors to consider to optimally image the hippocampus and criteria to diagnose medial temporal sclerosis are emphasized.

A prospective evaluation of cognitive decline in early Huntington's disease: functional and radiographic correlates.

We examined prospectively the relationship between progressive disability in Huntington's disease (HD) and concomitant alterations in neuropsychological functioning and brain imaging indices in a cohort of 60 patients who were enrolled and followed for 30 to 42 months in a controlled clinical trial. Standardized measures of functional capacity and neuropsychological performance were collected, and CT was performed, at regular intervals every 6 to 12 months. Psychomotor skills showed the most significant and consistent decline among the cognitive functions assessed. Memory disturbances were already present at the time of enrollment, but memory did not deteriorate until patients reached advanced stages. Other cognitive operations, such as visual construction and semantic knowledge, manifested small and variable changes over time. CT indices of striatal atrophy correlated only with changes in psychomotor function, while the CT index of frontal atrophy weakly predicted memory and semantic knowledge scores at 42 months. These results confirmed earlier cross-sectional findings and extended our knowledge of the evolution of cognitive dysfunction in HD.

The role of nonionic myelography in the diagnosis of lumbar disc herniation.

RATIONALE AND OBJECTIVES: The accuracy and safety of nonionic myelography, unenhanced computed tomography (CT), and magnetic resonance (MR) in the diagnosis of lumbar disc herniation are reviewed. The comparative costs of these tests are also considered. METHODS: The accuracy of imaging tests that diagnose disc herniations was established by conducting a Medline search between 1985 and 1992. The morbidity associated with these tests are less formally established from selected articles. Finally, the mediocre reimbursement rates of these tests are reviewed. RESULTS AND CONCLUSIONS: The evolution of nonionic contrast media from the first to the second generation has been accompanied by a notable decrease in adverse reactions. Although nonionic myelograms are now better tolerated by patients, noninvasive imaging with CT and MR imaging has become as accurate as or more accurate than lumbar myelography, and should replace it as a screening test. Computed tomography may have advantages over MR imaging when issues of availability and cost are considered. In contrast to lumbar myelography, CT myelography may continue to be a useful method for clarifying ambiguous results of noninvasive tests. The morbidity associated with CT myelography can be minimized by using low doses of a nonionic agent, keeping the patient well hydrated, and using a small lumbar puncture needle. The incidence of adverse reactions can be expected to decrease further as new nonionic dimers become clinically available.

The accuracy of magnetic resonance imaging in patients with suspected multiple sclerosis. The Rochester-Toronto Magnetic Resonance Imaging Study Group.

OBJECTIVE: To design and implement a methodologically rigorous study to examine the accuracy of magnetic resonance imaging (MRI) in a patient population clinically suspected of having multiple sclerosis (MS). DESIGN AND SETTING: Three hundred three patients, who were referred to two university medical centers because of the suspicion of MS, underwent MRI of the head and double-dose, contrast-enhanced computed tomography (CT) of the head. The images were read by two observers individually and without knowledge of the clinical course or final diagnosis. Patients were followed up for at least 6 months and reevaluated clinically with subsequent neurological examination. Final diagnosis (MS or not MS) was made by a panel of neurologists on the basis of the clinical findings at presentation, those that developed during follow-up, and other diagnostic tests. The results of the imaging procedures were excluded to avoid incorporation bias. Diagnostic accuracy was assessed using receiver-operating characteristic analysis and likelihood ratios. RESULTS: Magnetic resonance imaging of the head was considerably more accurate than CT in diagnosing MS. The area under the receiver-operating characteristic curve for MS was 0.82 (compared with 0.52 for CT) indicating that MRI was a good but not definitively accurate test for MS. A "definite MS" reading on an MRI of the head was specific for MS (likelihood ratio, 24.9) and essentially established the diagnosis, especially in patients clinically designated as "probable MS" before testing. However, MRI of the head was negative for MS in 25% and equivocal in 40% of the patients considered to have MS by the diagnostic review committee (sensitivity, 58%). CONCLUSIONS: Magnetic resonance imaging of the head provided assistance in the diagnosis of MS when lesions were visualized. Its ability far exceeded imaging with double-contrast CT. The sensitivity and, therefore, the predictive value of a negative MRI result for MS were, however, not sufficiently high for a normal MRI to be used to conclusively exclude the diagnosis of MS.

Traumatic brain injuries: predictive usefulness of CT.

The computed tomographic (CT) scans from 72 patients with traumatic brain injury were reviewed to determined whether a specific type, location, or size of lesion correlated with changes in neurologic function (assessed with the Glasgow Coma Scale [GCS]), patient outcome (assessed with the Glasgow Outcome Scale [GOS]), or catecholamine levels. The lesions were classified as focal or diffuse. GOS changed as a function of lesions size (P = .00004) in the 48 patients with focal hemorrhages, regardless of whether the lesions were intra- or extraaxial, and in the 19 patients with normal CT scans. Patients with lesions larger than 4,100 mm3 had a twofold greater risk of a poor outcome than patients with smaller lesions (100% vs 50%). Patients with normal CT scans were significantly more likely to have mild neurological dysfunction or none than patients with abnormal CT scans (P = .03), but lesion location, skull fracture, and pineal shift were not significant predictors of GCS or GOS scores. A positive relationship existed between lesion size and both plasma norepinephrine and epinephrine levels (P less than .02); a significant relationship existed between lesion size and GCS score (P = .02).

Clinical evaluation of stenosis of the carotid bifurcation with magnetic resonance angiographic techniques.

We evaluated the images of 60 carotid artery bifurcations in 31 patients suspected to have carotid artery disease who underwent invasive carotid angiography and combined two-dimensional, phase-sensitive and a gradient-echo magnetic resonance angiography. The phase scans consisted of seven serial projections that were obtained at 20 degrees intervals (11.0 minutes) around the carotid bifurcation; the gradient-echo (GRASS) scans were composed of 11 axial images (2.4 minutes) acquired through the bifurcation. The two magnetic resonance angiographic techniques yielded complementary pieces of information and were used together to compare magnetic resonance angiography with invasive angiography. Comparison of magnetic resonance and invasive angiograms of the 60 carotid arteries shows that the sensitivity (86%) and specificity (92%) of the magnetic resonance angiographic techniques we used to diagnose clinically significant carotid stenosis approach but do not reach those of invasive angiography.

Evaluation of the carotid artery bifurcation: comparison of magnetic resonance angiography and digital subtraction arch aortography.

Thirty-four carotid artery bifurcations were examined using both magnetic resonance angiography (MRA) and digital subtraction arch aortography to determine their accuracy when compared to selective carotid angiography. The sensitivity of MRA was 73% and its specificity was 91% when compared with selective carotid angiography. The sensitivity of arch aortography was 27% and its specificity was 100%.

A comparison of default and reduced bandwidth MR imaging of the spine at 1.5 T.

The value of a reduced bandwidth MR imaging technique was tested prospectively in 51 spinal MR examinations by using default (16 kHz) bandwidth, 2000/30, 90 (TR/TEs) and 600/30, and reduced (8 kHz) bandwidth, 2000/48, 92 and 600/30, techniques at 1.5 T. Bandwidth reduction was used to maintain the signal-to-noise ratio for a reduced scan time. Concerns have been raised as to the effect of bandwidth reduction at high field, since a savings in time or an increased signal-to-noise ratio occur at the expense of increased chemical shift misregistration artifact. However, when appreciable, the chemical shift-related artifact in the spine was typically located in the frequency-encoding direction at the vertebral body/disk space interface or the dural sac/epidural fat interface in the lower lumbosacral region and was easily distinguished from pathologic lesions. There were no missed diagnoses with the reduced bandwidth technique. This study suggests that chemical shift-related artifact will rarely be confused with pathology by an experienced reader and suggests a clinical role for the bandwidth technique to decrease scanning time in uncooperative patients or to allow acquisition of additional imaging planes in a reasonable time.

Gadolinium-DTPA-enhanced magnetic resonance scanning in cerebellopontine angle tumors.

Magnetic resonance (MR) imaging has quickly emerged and already replaced computerized tomography (CT) in the evaluation of cerebellopontine angle (CPA) lesions, although even MR scanning may occasionally yield equivocal results. We recently studied six patients with a new MR image-enhancing contrast, gadolinium-DTPA (Gd-DTPA). All patients were suspected of having CPA pathology, and the standard MR scan was either negative, equivocal, or left unanswered questions regarding confirmed lesions. The Gd-DTPA-enhanced MR scan confirmed tumors or added useful information in five of six patients.

Reduced-bandwidth MR imaging of the head at 1.5 T1.

A decrease in the magnetic resonance (MR) imaging bandwidth can be used to increase the signal-to-noise ratio (S/N) at constant imaging time or to maintain the S/N for reduction of imaging time. The effect of bandwidth reduction from the default value of 16 kHz to 8 kHz was evaluated prospectively in 50 patients referred for MR imaging of the head. On intermediate (2,000/30 [repetition time msec/echo time msec]) and more T2-weighted (2,000/90) studies, there were no definite missed diagnoses and no diagnostically important changes in lesion characteristics when the reduced-bandwidth technique was used to obtain half- or quarter-time studies, excluding differences attributable to unintentional changes in patient position between image acquisitions. Chemical shift misregistration artifacts associated with reduced bandwidth are easily recognized with experience and do not interfere with diagnosis, as the artifacts occur in characteristic locations and diminish in most anatomic locations with increasing echo time. This study suggests the feasibility of reduced-bandwidth techniques in clinical MR imaging of the head at high field strength to achieve an increased S/N, to decrease imaging time, or to obtain images in additional projections.