Measuring diffusion of solutes into intervertebral disks with MR imaging and paramagnetic contrast medium.

BACKGROUND AND PURPOSE: Experimental studies have shown that solutes diffuse more slowly into degenerated intervertebral disks than into normal disks. A noninvasive clinical study of diffusion in intervertebral disks is not generally available. Our purpose was to evaluate contrast-enhanced MR images to study diffusion in normal and degenerated lumbar intervertebral disks. METHODS: The change in signal intensity (as a proportion of baseline signal intensity) was calculated in lumbar intervertebral disks on MR images obtained before and after injection of intravenous contrast medium in 15 patients with low back pain. The intervertebral disks were classified as normal or degenerated on the basis of the MR appearance. Postoperative disks and degenerative intervertebral disks with a "high-intensity zone" were excluded. The changes in signal intensity as a proportion of baseline signal intensity were compared in degenerated disks and normal disks and the differences tested for statistical significance. RESULTS: After intravenous administration of a gadolinium complex, signal intensity in normal intervertebral disks increased an average of 36% of baseline. In intervertebral disks with signs of degeneration, it increased an average of 21% of baseline. The difference was significant. CONCLUSION: The study shows that diffusion into normal human lumbar intervertebral disks can be evaluated with MR imaging combined with intravenous contrast medium. With suitable MR techniques, the relationship between diffusion and disk degeneration, and the effect of trauma, drugs, and nutrition on disk degeneration can be studied noninvasively.

Diffusion into human intervertebral disks studied with MR and gadoteridol.

PURPOSE: To determine the feasibility of measuring diffusion into human intervertebral disks by means of MR imaging with an intravenous nonionic gadolinium complex (gadoteridol). METHODS: In 18 patients undergoing lumbar spine MR imaging, signal intensity was measured in the intervertebral disks after a dose of 0.1 mmol/kg and after a supplemental dose of 0.2 mmol/kg. RESULTS: Signal intensity in the intervertebral disks increased with both gadoteridol doses. A greater increase was consistently achieved with the 0.3 mmol/kg (total) dose than with the 0.1 mmol/kg dose. The increase was greater near the endplates than in the midportion of the disk. CONCLUSION: Diffusion into human intervertebral disks can be detected with MR imaging after intravenous administration of gadoteridol. MR imaging with a paramagnetic contrast medium can be used to study diffusion into disk cartilage in vivo and noninvasively.

Location of the sensorimotor cortex: functional and conventional MR compared.

PURPOSE: To determine the value of functional MR imaging to supplement conventional MR imaging for locating the rolandic cortex. METHODS: Parasagittal MR images acquired in conjunction with functional MR images were reviewed. The central sulcus was identified on the MR images by conventional parcellation methods. In the functional MR images, the sensorimotor cortex (rolandic cortex) was identified by the activation secondary to finger and thumb movement or tactile stimulation of the palm. The location of the central sulcus and rolandic cortex was compared. RESULTS: In 18 of 23 studies, the central sulcus selected by anatomic criteria coincided exactly or approximately with the cortex activated by the motor or sensory tasks. In two cases of tumor, the rolandic cortex could be located by means of the activation, but the central sulcus was not identified because of severe distortion of anatomic landmarks. In two volunteers, the central sulcus identified by anatomic landmarks did not coincide with the activated cortex. CONCLUSION: This study demonstrates that functional imaging supplements anatomic imaging in locating the sensorimotor cortex. Functional MR imaging may be a useful adjunct to conventional MR imaging to determine noninvasively the proximity of eloquent brain to focal brain lesions.

Safety and efficacy of iopromide in cerebral arteriography.

RATIONALE AND OBJECTIVES: Iopromide is a new nonionic monomeric contrast medium for cerebral arteriography. This agent has been approved for sale in over 45 countries; however, it is still undergoing clinical review in the United States. This study evaluated the safety and efficacy of iopromide in comparison with two other nonionic contrast media. METHODS: A total of 173 patients participated in the study, which was prospective, double-blind, and randomized. In two centers, patients received iopromide or iohexol; in the other three centers, patients received iopromide or iopamidol. Adverse events were monitored by investigators, and efficacy was evaluated by grading the radiographic images. RESULTS: Most adverse events were mild or moderate in severity; all resolved completely. Twenty-one percent of patients given iopromide were reported to have a drug-related adverse event, versus 44% of patients given a comparator. No statistically significant difference emerged between iopromide and the comparators with regard to efficacy. CONCLUSIONS: These study results indicate that iopromide is a safe and effective contrast medium for cerebral angiography.

Focal hyperintensities in cerebral white matter on MR images of asymptomatic volunteers: correlation with social and medical histories.

OBJECTIVE: Previous attempts to explain the presence of focal hyperintensities in the cerebral white matter on MR images have focused on the patient's age and cardiovascular risk factors. The purpose of this study was to survey many variables in subjects' social, medical, and surgical histories to identify those factors associated with focal hyperintensities in asymptomatic persons. SUBJECTS AND METHODS: Asymptomatic volunteers were examined with MR imaging of the head and questioned concerning smoking history; chemical dependence; alcohol consumption; medical history (e.g., high blood pressure, kidney disease); surgical history (e.g., for appendix, gallbladder); medications (e.g., antihypertensives, analgesics); and other historical family and social variables. Vital signs were recorded. Focal hyperintensities were counted by observers who were not provided any information about the subjects other than that they were either volunteers or patients. Each of the variables in the history was tested for an association with the number of focal hyperintensities seen on MR images. RESULTS: A statistically significant positive association was found between both age and the use of antihypertensive medications and the number of focal hyperintensities. Associations were also found between the number of focal hyperintensities and diastolic and systolic blood pressures at the time of MR imaging, but these associations did not reach statistical significance. No other variables in the medical, surgical, or social histories were found to be significantly related to the number of focal hyperintensities. CONCLUSION: Age and the use of antihypertensive medications were the only significant risk factors identified in respect to focal hyperintensities of the cerebral white matter.

High-signal foci on MR images of the brain: observer variability in their quantification.

Foci of high signal in the cerebral white matter are common incidental findings on MR images of the brain of control subjects or patients with a variety of diseases. Although the number of foci has been reported to correlate with age and several risk factors, the degree of observer variability in quantifying foci has not been reported. We used kappa statistics to determine radiologists' agreement in counting high-signal-intensity foci on MR images obtained in healthy volunteers and in patients with hypertension. Before interpreting the images, one pair of radiologists studied 30 routine MR images and reached consensus on differentiating high-signal foci from other foci of high intensity caused by normal structures (e.g., deep gyri or Virchow-Robin spaces). These two observers than independently determined the number of foci in the study group. Using their own criteria, other radiologists independently counted the foci. Agreement between observers was determined with the kappa statistic. The results showed fair agreement between the radiologists who first reached a consensus in counting foci of hyperintensity and poor agreement between the other observers. We conclude that in order to compare the frequency of foci of hyperintensity in different groups of patients, observer variability must be controlled. Studies without proper control subjects may lead to incorrect conclusions regarding the correlation of focal hyperintensities and various risk factors.

Quantitative MR in the diagnosis of multiple sclerosis.

In patients with multiple sclerosis (MS), the apparently uninvolved cerebral white matter between demyelinated plaques may have biochemical abnormalities. To what degree the changes in the white matter contribute to symptomatology in MS is unknown. In 39 patients with multiple sclerosis, and in 39 age-matched nondiseased volunteers, T1 and T2 were calculated from spin-echo images in four regions of apparently uninvolved white matter. In three of four white matter areas, the average T1 and T2 were significantly longer in the patients than in the controls. The T1 correlated with the disability, measured by the Kurtzke Extended Disability Status Scale, although the correlation was marginally significant. The results suggest that in patients with MS, white matter disease that is not visualized in MR as distinct foci of abnormal signal intensity may contribute to disease burden and disability.

T1 and T2 in the cerebrum: correlation with age, gender, and demographic factors.

The authors measured the T1 and T2 of cerebral tissue in 164 volunteers aged 5-90 years and correlated T1 and T2 with age, gender, and various demographic variables. A weak correlation with statistical significance was found between age and T1 and T2 in white and gray matter structures. The T1 and T2 in the telencephalon increased by about 0.1% per year. No correlation of T1 or T2 with any other demographic, life-style, or medical factors was found.

Multiple sclerosis: specificity of MR for diagnosis.

The specificity of magnetic resonance (MR) imaging in the diagnosis of multiple sclerosis (MS) has not been measured systematically. Conventional MR head images with sagittal localizer and axial multiple-echo sequences with long repetition times were obtained in 92 patients with clinically verified MS (Schumacher criteria), 100 healthy volunteers, 60 subjects with hypertension, and eight patients with dementia. Two readers, without the aid of any clinical or demographic information, classified each of the 260 studies as MS or not MS. The readers classified the studies again after being supplied with the subjects' ages and sex. True-negative and true-positive diagnoses of MS were tabulated. The specificity of the MR diagnosis of MS (true-negative results in proportion to all non-MS studies) was 95%-99% with all the control groups included. There is a small risk of misinterpreting incidental periventricular white matter foci as plaques of MS in MR studies.

Contrast enhancement in spinal MR imaging.

We evaluated 44 patients with suspected spinal tumors or previous laminectomies with gadolinium-DTPA MR imaging in order to characterize the enhancement in normal, postoperative, and neoplastic intraspinal tissue. Using the signal intensity of CSF as an internal control, we calculated the percentage increase in signal intensity from pre- to postgadolinium studies. Tumors (astrocytoma, ependymoma, schwannoma) enhanced 70-350%; epidural scar, normal epidural venous plexus, and dorsal root ganglion enhanced up to 200%. Contrast enhancement does not per se distinguish neoplastic from normal tissue. Enhancement with gadolinium-DTPA appeared to increase the conspicuousness of intramedullary tumors but not intraosseous metastases. We believe that gadolinium-enhanced MR imaging is a valuable adjunct to routine MR imaging in the evaluation of intraspinal neoplastic processes and may be useful in delineating normal and postoperative structures in the spinal canal.

Alzheimer disease: quantitative analysis of I-123-iodoamphetamine SPECT brain imaging.

To enable a more quantitative diagnosis of senile dementia of the Alzheimer type (SDAT), the authors developed and tested a semiautomated method to define regions of interest (ROIs) to be used in quantitating results from single photon emission computed tomography (SPECT) of regional cerebral blood flow performed with N-isopropyl iodine-123-iodoamphetamine. SPECT/IMP imaging was performed in ten patients with probable SDAT and seven healthy subjects. Multiple ROIs were manually and semiautomatically generated, and uptake was quantitated for each ROI. Mean cortical activity was estimated as the average of the mean activity in 24 semiautomatically generated ROIs; mean cerebellar activity was determined from the mean activity in separate ROIs. A ratio of parietal to cerebellar activity less than 0.60 and a ratio of parietal to mean cortical activity less than 0.90 allowed correct categorization of nine of ten and eight of ten patients, respectively, with SDAT and all control subjects. The degree of diminished mental status observed in patients with SDAT correlated with both global and regional changes in IMP uptake.

T1 and T2 measurements on a 1.5-T commercial MR imager.

In order for relaxation times to be used in clinical diagnosis, the precision of the measurement must be determined. The authors measured T1, T2, and proton density in a phantom and in human volunteers to determine the reproducibility of the method. The coefficient of variance of T1 measurements in the phantom during a 15-month period with two software upgrades was 5%. Variance of T2 measurements with any given software was 4% or less, and overall in the 15-month period, with two software changes, the T2 reproducibility was between 6% and 9%. The reproducibility is sufficiently high that precise clinical measurements of T1, T2, and proton density are feasible.

Sensitivity of Gd-DTPA-enhanced MR imaging of benign extraaxial tumors.

The effect of gadolinium diethylenetriaminepentaacetic acid (DTPA) on the sensitivity of cranial magnetic resonance (MR) imaging was measured in a prospective blinded study. Twenty-two consecutive patients with benign extraaxial tumors underwent MR imaging on a 1.5-T system without and with intravenous administration of Gd-DTPA. Readers independently interpreted the unenhanced and enhanced images without clinical information. The interpretations were compared with the anatomically verified diagnoses. Gd-DTPA improved the sensitivity of MR imaging for benign extraaxial tumors, especially in cases of residual or recurrent acoustic neuromas, multiple tumors (e.g., neurofibromatosis), or inconclusive unenhanced MR images. Enhancement with Gd-DTPA impaired the identification of a skull base tumor.

Benign extraaxial tumors: contrast enhancement with Gd-DTPA.

Meningiomas, acoustic neuromas, and other benign extraaxial tumors have little contrast with adjacent brain tissue on conventional magnetic resonance (MR) images. The contrast enhancement produced by intravenous administration of 0.1 mmol/kg of gadolinium-DTPA in these tumors was measured on T1 MR images. Acoustic neuromas showed the greatest enhancement (average, 310%), meningiomas the next greatest (average, 180%), and neurofibromas, glomus tumors, and pituitary microadenomas the least enhancement. The degree of enhancement was almost always greater at 3 minutes than at 25 or 55 minutes. Contrast between the tumor and adjacent tissue resulted from tumor enhancement in neuromas, meningiomas, and neurofibromas and from enhancement of the surrounding tissue in pituitary microadenomas.

A blinded clinical comparison of MR imaging and CT in neuroradiology.

The sensitivity and specificity of magnetic resonance (MR) imaging and computed tomography (CT) were compared in blinded readings of images of a consecutive series of patients with subsequently proved diagnoses. Overall, MR imaging was less sensitive than CT because of its lower sensitivity in detecting benign tumors. With a similar experimental protocol, the effects of technical refinements or contrast media on the sensitivity of MR imaging can be determined.