Sodium MR Neuroimaging.

Sodium MR imaging has the potential to complement routine proton MR imaging examinations with the goal of improving diagnosis, disease characterization, and clinical monitoring in neurologic diseases. In the past, the utility and exploration of sodium MR imaging as a valuable clinical tool have been limited due to the extremely low MR signal, but with recent improvements in imaging techniques and hardware, sodium MR imaging is on the verge of becoming clinically realistic for conditions that include brain tumors, ischemic stroke, and epilepsy. In this review, we briefly describe the fundamental physics of sodium MR imaging tailored to the neuroradiologist, focusing on the basics necessary to understand factors that play into making sodium MR imaging feasible for clinical settings and describing current controversies in the field. We will also discuss the current state of the field and the potential future clinical uses of sodium MR imaging in the diagnosis, phenotyping, and therapeutic monitoring in neurologic diseases.

Cerebral infarction and migraine: clinical and radiologic correlations.

Cerebral infarction was documented by arteriography and serial computed cranial tomography (CT) in four young adults (ages 16 to 32 years) with migraine. In one case, posterior cerebral artery occlusion produced a deep parietotemporal infarct. The other three cases all had frontotemporal infarcts (one hemorrhagic) in the territory of the middle cerebral artery, without major arterial occlusion. Two infarcts produced lasting neurologic deficits; one was associated with mild, transitory symptoms, and one was asymtomatic. Laboratory investigations in two cases revealed no hematologic or cardiovascular predisposition to cerebrovascular disease. Cerebral infarction, as revealed by CT, may be more prevalent in "complicated" migraine than is generally appreciated. Such lesions may or may not develop in chronologic and anatomic relationship to the headache, and may involve either large or small arteries. The prognosis for functional recovery, based on this limited sample, seems favorable.

Occult arteriovenous malformation of the brainstem simulating multiple sclerosis.

A patient who proved to have an angiographically occult arteriovenous malformation of the brainstem and cerebellum was thought to have multiple sclerosis for 20 years, because of fluctuating brainstem symptoms and signs. Although the computed tomographic (CT) appearance of the lesion suggested a vascular malformation, because it bridged the subarachnoid space between the brainstem and cerebellum, an arteriogram was normal. This report stresses the importance of CT in making the diagnosos of occult arteriovenous malformations of the brainstem. On CT scan, these lesions generally have a high-density multiform appearance, which may enhance with contrast infusion. This lesion should be suspected clinically when there are fluctuating neurologic symptoms and signs attributable to the same neuroanatomic location within the brainstem. Surgical biopsy may confirm the diagnosis, but attempts to remove these lesions from the brainstem parenchyma are hazardous and probably are not indicated, considering the chronic and relatively benign course.

Arthrography using perfluorocarbon compounds.

The neat liquid and an emulsion of two perfluorocarbon compounds were injected into the knee joints of dogs and a human cadaver to investigate their applicability for arthrography. Excellent delineation of joint structures was observed for as long as 24 hours, but after 24 hours each contrast agent leaked out of the joint capsule into surrounding tissue. Light microscopy of joint tissue revealed a synovial proliferative reaction and a foreign-body granuloma reaction in surrounding tissues. No clinically apparent adverse side effects were evident in the test animals.

Time-density evaluation of the liver after iosulamide meglumine: a tissue-specific CT contrast agent.

Iosulamide meglumine, a new intravenous biliary contrast agent, was evaluated as a potential hepatic contrast agent utilizing computed tomographic scanning. Time-density data in dogs were generated following 56.7 and 75.6 mg iodine/kg body weight. The iodine was administered both as an iosulamide meglumine bolus injection and a 0.77 ml/min infusion. The greatest increase in x-ray attenuation (24 HU) was observed within 45 minutes after the 75.6 mg iodine/kg body weight infusion technique, which resulted in excellent hepatic opacification. The long duration of increased x-ray attenuation of hepatocytes produced by iosulamide meglumine would be useful in the CT detection of hepatic mass lesions which do not contain normally functioning hepatic cells.

Contrast media tonicity. Part II. Isotonic ioxaglate vs. standard renografin for IV-DSA evaluation of the carotid bifurcation, a double-blind prospective clinical trial.

Laboratory research has suggested that isotonic contrast media may be optimal for intravenous digital subtraction angiography (IV-DSA) by generating taller, narrower time-concentration curves. Clinical investigation of low osmolality contrast media has suggested that less patient discomfort is encountered with low-osmolality contrast media than with standard, high-osmolality agents. In order to directly compare isotonic contrast media with a standard hypertonic contrast media, isotonic ioxaglate (Hexabrix-20) was compared with Renografin-76 in a double-blind prospective clinical trial for IV-DSA examination of the carotid artery bifurcation. Isotonic ioxaglate produced superior contrast medium time-opacification curves and produced superior images across four scales of image quality: anatomic "openness" of the carotid bifurcation, contrast level within the carotid vessels, bone misregistration artifact over the bifurcation, and air (soft tissue) misregistration. The bilateral overall score for isotonic ioxaglate was 1.68 vs. 1.37 for Renografin-76, a 23% superiority. The bulk of the superiority occurred in the contralateral carotid artery. Over the four scales, isotonic ioxaglate was 37% better in image quality of the contralateral carotid artery bifurcation. Since the contralateral carotid artery is very often difficult to visualize during IV-DSA, isotonic ioxaglate represents a significant improvement for this imaging modality.

Some useful concepts of matched filtering in intravenous digital subtraction angiography.

Using computer calculations and assumed contrast bolus curves, several aspects of the application of temporal integration methods and matched filtering to intravenous digital subtraction angiography (IV-DSA) were studied. The topics included the improvement in signal-to-noise ratio (SNR) of the final image provided by simple integration, a comparison of the SNR performance of matched filtering and extensive integration, the degradation of SNR caused by the motion of noniodinated objects and the sensitivity of SNR to variations in DSA bolus dynamics from patient to patient. Additionally the dependence of matched filter SNR on exposure position and duration was both estimated and demonstrated with clinical DSA images. The results indicate that a substantial improvement in SNR can be obtained with only moderate integration increasing to a two X improvement for longer durations. Integration methods are able to withstand moderate durations (2 seconds) of motion and still provide image quality superior to more conventional DSA results.

A procedure for using proton magnetic resonance imaging to determine stereotaxic coordinates of the monkey's brain.

Because of great inter-individual variability in the sizes and configurations of monkey brains, consistent intracerebral stereotaxic placements are not possible when a general brain atlas is relied upon to derive placement coordinates. We describe a procedure that allows the determination of brain atlases for individual monkeys using proton magnetic resonance imaging and the translation of image coordinates to stereotaxic coordinates. The latter is accomplished by chronically implanting glass beads filled with copper sulfate into the skull to establish a plane horizontal to the stereotaxic plane and to provide reference points for zeroing stereotaxic carriers during intracerebral implants. The efficacy of this procedure was confirmed experimentally.

Infantile Krabbe disease: complementary CT and MR findings.

This case report of the infantile form of Krabbe disease in a 2 1/2-month-old boy illustrates the complementary findings that may be seen on CT and MR scans. The key finding on the CT scan was increased density in a bilateral symmetrical distribution involving the thalami with extension into the centrum semiovale. The MR scan, on the other hand, more clearly showed demyelination in the brain stem and cerebellum. In cases in which this involvement is minimal or absent, the MR scan may fail to detect an abnormality, and a CT scan will, therefore, still be necessary to detect characteristic abnormalities.

Cerebrospinal fluid flow measured by phase-contrast cine MR.

PURPOSE: This prospective study was designed to establish the temporal and quantitative relationship between blood flow and cerebrospinal fluid (CSF) flow using a phase-contrast cine MR pulse sequence. METHODS: A cine phase-contrast MR pulse sequence using peripheral gating was used to measure CSF flow direction and velocity. Data were acquired continuously and interpolated into 16 images throughout the cardiac cycle. RESULTS: The timing of systolic CSF flow in the cervical subarachnoid space (SAS) correlated very closely to the brain arteriovenous blood flow difference during the cardiac cycle. This arteriovenous difference was a measure of brain expansion. Aqueduct CSF flow during the cardiac cycle differed from SAS flow in that systolic flow was delayed in comparison with systolic cervical SAS flow. The normal aqueductal oscillatory flow volume was 1.7 +/- .4 mL/min or 0.03 +/- 0.01 mL per cardiac cycle. This represented 14.5% +/- 3.1% of the total CSF flow and tissue displacement through the incisura which was 14.5 +/- 2.2 mL/min or 0.22 +/- 0.03 mL per cycle. CSF oscillatory flow volume in the cervical SAS was 39.0 +/- 4.0 mL/min or 0.65 +/- 0.08 mL per cycle. CONCLUSION: CSF flow can be measured. Results in healthy subjects show relatively low oscillatory flow through the aqueduct which is slightly out of phase (delayed) compared with SAS CSF flow.

Optimizing MR imaging for detecting small tumors in the cerebellopontine angle and internal auditory canal.

Relative resolving power was used to determine the optimal MR imaging pulse sequence for detecting small tumors of the internal auditory canal and the cerebellopontine angle. Resolving power takes into consideration these important image characteristics: signal-to-noise ratio, contrast, and spatial resolution. The study was performed on a 1.5-T magnet using a 256 X 256 matrix and a 3-mm slice thickness. The TR ranged from 400-2000 msec; the number of excitations was either two or six; and the pixel size was 0.94, 0.78, or 0.63 mm. Theoretical calculations of relative resolving power were compared with the relative resolving power of 45 control patients and 15 patients with small tumors of the cerebellopontine angle or internal auditory canal. A TR of 800 msec was optimal from theoretical calculations and proved optimal in control and tumor patients. Scans obtained with TR = 2000 msec, TE = 80 msec were inferior to short TR scans; such scans could fail to detect intracanalicular tumors. The relative resolving power in patients exceeded theoretical calculations because of greater than expected image contrast caused by low CSF signal intensity secondary to CSF pulsation.

Mycotic aneurysm in angiitis associated with herpes zoster ophthalmicus.

Varicella zoster (VZ) is an unusual cause of CNS angiitis, usually occurring in older patients and immunocompromised hosts. The infection most commonly presents as herpes zoster ophthalmicus with contralateral hemiplegia. Mycotic aneurysm formation associated with VZ angiitis is rare. We report two cases of VZ angiitis with mycotic aneurysm formation (both aneurysms eventually ruptured) and one case of probable VZ angiitis with distal carotid occlusion and cerebral infarction. The CT and angiographic appearances, clinical course, and histopathology are presented.

Qualitative phase contrast MRA in the normal and abnormal circle of Willis.

PURPOSE: To determine the direction of blood flow in the circle of Willis using a 3-D phase contrast MR angiographic (MRA) technique with high spatial resolution. SUBJECTS: Fifty healthy subjects and 15 patients with occlusive disease were studied using 3-D phase contrast MRA. RESULTS: In the 50 normal subjects, 39 (78%) had detectable flow in one or both posterior communicating arteries. In 24 (48%) of these subjects, flow was detected in both posterior communicating arteries, whereas unilateral flow was detected in 15 (30%). In 36 (92%) of the 39 normal subjects, flow in the posterior communicating artery was from anterior to posterior with only 3 (8%) showing reverse flow from posterior to anterior. The A1 segment of both anterior cerebral arteries was identified in 100% of normal subjects with flow in the expected direction from carotid to the A2 segment. In patients with carotid occlusion, the pattern of flow in the circle of Willis was altered with reversed flow in the ipsilateral posterior communicating artery and sometimes in the ipsilateral A1 segment. An ipsilateral posterior communicating artery was present in 10 of 17 occluded carotid arteries, all showing reversed flow. CONCLUSION: 3-D phase contrast MRA provides useful information about the hemodynamics of normal and abnormal blood flow in the circle of Willis.

Magnetization transfer MR of the normal adult brain.

PURPOSE: To establish a normal baseline of the percent magnetization transfer of gray (cortical and deep) and white matter structures in the brain in healthy adults and to determine whether there are adult age-related differences in these measurements. METHODS: Axial T1-weighted scans (800/20 [repetition time/echo time]) with and without magnetization transfer were prospectively performed on a 1.5-T MR imaging unit on 68 healthy patients (aged 20 to 76 years). Presaturation and postsaturation magnetization transfer images were obtained using an on-resonance binomial pulse. All patients had normal MR scans on all pulse sequences. A calculated "difference" image was used to calculate the percent magnetization transfer in multiple specific regions of the brain. In each hemisphere, 9 discrete areas of cortical and deep gray matter and 29 areas of white matter were measured in 68 patients to generate age-related changes in percent magnetization transfer in these anatomic regions. Ranges of normal percent magnetization transfer in each of the 38 measures were established. RESULTS: The percent magnetization transfer of the gray matter (28% +/- 2%) was lower than that of the white matter (36% +/- 2%). There was no statistically significant difference in the percent magnetization transfer in different areas of gray matter. Deep white matter in the different lobes (percent magnetization transfer, 31% to 38%) also showed no differences by age. Percent magnetization transfer was the highest in the genu of the corpus callosum (42%), and this was statistically significant compared with other white matter measurements. CONCLUSION: There were no statistically significant age-related variations in the percent magnetization transfer in healthy adults in gray or white matter. These percent magnetization transfer measurements provide baseline normative data, which can be used to measure the extent and severity of white matter changes in disease states.

Improved detection of enhancing and nonenhancing lesions of multiple sclerosis with magnetization transfer.

PURPOSE: To determine whether magnetization transfer imaging can improve visibility of contrast enhancement of multiple sclerosis plaques. METHODS: Fifty-nine enhancing and 63 nonenhancing lesions in 10 patients with multiple sclerosis were evaluated to calculate contrast-to-noise ratios on conventional T1-weighted and T1-weighted magnetization transfer images. The signal intensity of the lesion and the background (white matter) were measured on precontrast T1-weighted and T1-weighted magnetization transfer images (800/20/1 [repetition time/echo time/excitations]) and on postcontrast T1-weighted and T1-weighted magnetization transfer images. Mean contrast-to-noise ratios was calculated for all lesions. RESULTS: The contrast-to-noise ratio was significantly higher for enhancing and nonenhancing lesions on T1-weighted magnetization transfer images than on conventional T1-weighted images. For enhancing lesions, the contrast-to-noise ratio was significantly higher on postcontrast T1-weighted magnetization transfer images, 32 +/- 2 compared with 21 +/- 2 on conventional T1-weighted images. Fifty of the 59 enhancing lesions were seen on both the T1-weighted and the T1-weighted magnetization transfer images. Nine enhancing lesions were seen only on the postcontrast T1-weighted magnetization transfer images. In addition, of 63 nonenhancing lesions seen on proton-density, T2-weighted, and T1-weighted magnetization transfer images, 16 were not seen on the conventional T1-weighted images. Seven of the 63 nonenhancing lesions and 7 of the 59 enhancing lesions had high signal intensity on the precontrast T1-weighted magnetization transfer images suggestive of lipid signal, a finding not seen on the conventional precontrast T1-weighted images. CONCLUSION: Magnetization transfer improves the visibility of enhancing multiple sclerosis lesions, because they have a higher contrast-to-noise ratio than conventional postcontrast T1-weighted images. High signal intensity on both nonenhancing and enhancing lesions noted only on precontrast T1-weighted magnetization transfer suggests a lipid signal was unmasked. If magnetization transfer is used in multiple sclerosis patients, a precontrast magnetization transfer image is necessary.

Measure of magnetization transfer in multiple sclerosis demyelinating plaques, white matter ischemic lesions, and edema.

PURPOSE: To define the percentage of magnetization transfer of multiple sclerosis (MS) plaques, ischemic white matter lesions, and vasogenic edema to determine whether this measurement can help differentiate these entities. METHODS: Findings were compared in 25 patients with proved MS, 20 patients with white matter ischemic lesions, and 72 patients with white matter edema (caused by tumors, infections, or acute/subacute infarctions) in the periventricular system, centrum semiovale, and subcortical white matter. Magnetization transfer was performed using an on-resonance binomial pulse. The percentage of magnetization transfer of the normal white matter was also calculated. RESULTS: Magnetization transfer was significantly higher in white matter ischemic lesions (range, 31% to 38%; mean, 34% +/- 0.6%) than in demyelinating plaques of MS (range, 19% to 28%; mean, 22.5% +/- 1%) and in edema (range, 29% to 37%; mean, 30.2% +/- 0.4%). No statistical difference in percentage of magnetization transfer was found among lesions in the periventricular system (34% +/- 0.6%), centrum semiovale (35% +/- 0.5%), or subcortical white matter (33% +/- 0.6%), or in vasogenic edema associated with tumors, infections, or infarction. CONCLUSION: Differences in magnetization transfer suggest less change of demyelination in white matter ischemic lesions than in MS plaques and are significantly different in this respect from similar MS plaques. Magnetization transfer of edema was less than that of normal white matter or fell between ischemic abnormalities and MS plaques. Percentages of magnetization transfer below the mid-20% range is highly suggestive of demyelination. Vasogenic edema, our surrogate for increased water content of white matter, caused a decrease in the percentage of magnetization transfer.

Left-right temporal region asymmetry in infants and children.

Thirty-two consecutive cranial computed tomographic (CT) scans in normal infants ranging from 1 day to 3 years of age were evaluated for asymmetry of the temporal lobes as evidenced by differences in the size of the sylvian fissures. The left sylvian fissure was larger than the right in 23 of the 32 cases, which was statistically significant (p less than 0.0001). In five other cases the two sides were equal; in the four remaining cases, the right side was larger than the left. The results show that asymmetry of the temporal lobes can be demonstrated in vivo even at birth and that this asymmetry is a normal developmental difference between the two hemispheres and not secondary to an acquired abnormality.

Blood flow in major cerebral arteries measured by phase-contrast cine MR.

PURPOSE: To measure mean blood flow in individual cerebral arteries (carotid, basilar, anterior cerebral, middle cerebral, and posterior cerebral) using a cine phase contrast MR pulse sequence. METHODS: Ten healthy volunteers (22 to 38 years of age) were studied. The cine phase-contrast section was positioned perpendicular to the vessel of interest using oblique scanning planes. This pulse sequence used a velocity encoding range of 60 to 250 cm/sec. From the velocity and area measurements on the cine images, mean blood flow was calculated in milliliters per minute and milliliters per cardiac cycle. In the same subjects, transcranial Doppler measurements of blood velocity in these same vessels were also obtained. RESULTS: There was no difference in blood flow in the paired cerebral arteries. Carotid arteries had mean blood flow in the range of 4.8 +/- 0.4 ml/cycle, the basilar artery 2.4 +/- 0.2 ml/cycle, the middle cerebral artery 1.8 +/- 0.2 ml/cycle, the distal anterior cerebral artery 0.6 +/- 0.1 ml/cycle, and the posterior cerebral artery 0.8 +/- 0.1 ml/cycle. Overall, there was poor correlation between MR-measured and transcranial Doppler-measured peak velocity. CONCLUSION: Although careful attention to technical detail is required, mean blood flow measurements in individual cerebral vessels is feasible using a cine phase-contrast MR pulse sequence.

Natural history of experimental intracerebral hemorrhage: sonography, computed tomography and neuropathology.

The evolution of intracerebral hemorrhage was investigated in a canine model by high resolution sonography, computed tomography (CT), and neuropathologic examination. In 12 dogs, a parietal lobe hematoma was introduced by craniotomy. The sonographic appearance of acute hemorrhage was characteristic and consisted of a sharply circumscribed, homogeneous, highly echogenic lesion, the size and shape of which correlated closely to the area of increased density seen on the CT scan. This changed within 3-4 days to an echogenic rim surrounding a hypoechoic center. Histologically, this change corresponded to a loss of integrity of individual red blood cells. This occurred earliest in the hemorrhage center causing a hypoechoic center, while intact red blood cells at the periphery accounted for the echogenic rim. Shortly after the red blood cells lost their biconcave shape they began to lose their hemoglobin causing the hemorrhage to become isodense with surrounding brain on the CT scan. Faint contrast enhancement by CT was noted at this early stage and was related primarily to a mononuclear perivascular infiltrate at the edge of the hemorrhage. A collagen capsule formed around the hemorrhage over a 2 week period. This capsule slowly replaced intact red cells as the cause of the now shrinking echogenic rim. This capsule was also responsible for the increasing ring contrast enhancement around the resolving hemorrhage. The sequence of image changes seen on both CT and sonography in this experimental model closely resembled the findings seen in intracerebral hemorrhage in patients.

Experimental Staphylococcus aureus brain abscess.

The virulent organism Staphylococcus aureus produced brain abscesses that were quantitatively and qualitatively different from those caused by less virulent organisms. S. aureus abscesses created larger lesions, as earlier ependymitis, delayed progress toward healing, and caused areas of inflammatory escape outside the collagen capsule. Imaging tests revealed similar findings: the abscesses were larger, had more extensive central necrosis, and showed earlier evidence of ependymitis. This virulent organism also demonstrated that white matter is more susceptible than overlying gray matter to destruction by infection. The pattern of spread and other histologic findings suggest that collagen capsule formation has less of an infection "containment" function than was previously thought.