MR imaging of intrinsic inflammatory myelopathies.

The neuroimaging evaluation of patients with suspected inflammatory myelopathy is one of the more technically and interpretatively challenging MR examinations. This article reviews several recent MR imaging sequencing developments that have significantly improved spinal cord imaging. The clinical, pathologic, and MR imaging features of several of the more common inflammatory myelopathic-producing diseases also are discussed.

Flip angle dependence of experimentally determined T1sat and apparent magnetization transfer rate constants.

The purpose of this work was to develop a method for determining the T1sat and magnetization transfer (MT) rate constants by analyzing the slice-select flip angle dependent MT behavior of normal white and gray matter. The technique uses a high MT power, three-dimensional (3D) gradient-recalled echo (GRE) sequence, with a well chosen MT pulse frequency offset, such that the experimental conditions closely satisfy requisite assumptions for invoking a first order rate process for MT. Integral to this method is that the T1sat and MT ratio values are obtained under explicitly identical MT saturation conditions. The T1sat of white matter was found to be approximately 300 msec, and the MT rate constant was approximately 2.0 sec(-1). The T1sat of gray matter was approximately 500 msec, and the MT rate constant was 1.1 sec(-1). We also found a strong dependence of the MT rate constant on the slice-select flip angle used for the imaging sequence, independent of the MT saturation parameters. Strongly T1-weighted imaging sequences can result in the underestimation of the MT rate constant by 50%. Practical technical suggestions for quantitative MT experiments are put forth.

Magnetization transfer in neuroimaging.

Magnetization transfer (MT) imaging has become a focus of recent basic science and clinical investigations because of its unique physical basis of contrast, and the potential to quantify aspects of the biochemical structure and composition of tissues. In this article, basic theories of MT are discussed, and several practical MT pulse and sequence considerations are addressed. The clinical utility of MT techniques in MR angiography, postgadolinium T1-weighted scanning, and spine scanning are discussed. Highlights of quantitative MT studies for pathologic tissue characterization and for studies of patients with white-matter disorders such as multiple sclerosis are included, giving a comprehensive review of the neuroimaging application of MT.

T1-weighted three-dimensional magnetization transfer MR of the brain: improved lesion contrast enhancement.

PURPOSE: We developed and evaluated clinically T1-weighted three-dimensional gradient-echo magnetization transfer (MT) sequences for contrast-enhanced MR imaging of the brain. METHODS: A short-repetition-time, radio frequency-spoiled, 3-D sequence was developed with a 10-millisecond MT pulse at high MT power and narrow MT pulse-frequency offset, and the enhancing lesion-to-normal white matter background (L/B) and the contrast-to-noise (C/N) ratios on these images were compared with those on T1-weighted spin-echo images and on non-MT 3-D gradient-echo images in a prospective study of 45 patients with 62 enhancing lesions. In the 24 patients who had intracranial metastatic disease, the number of lesions was counted and compared on the three types of images. RESULTS: The MT ratio of normal callosal white matter was 55% on the MT 3-D gradient-echo sequences. The L/B and C/N on the MT 3-D gradient-echo images were more than double those on the 3-D gradient-echo images, and were significantly greater than those on the T1-weighted spin-echo images. In patients with metastatic disease, the MT 3-D gradient-echo images showed significantly more lesions than did the T1-weighted spin-echo or 3-D gradient-echo images. CONCLUSION: MT 3-D gradient-echo MR imaging improves the contrast between enhancing lesion and background white matter over that obtained with conventional T1-weighted 3-D gradient-echo and spin-echo imaging. MT 3-D gradient-echo imaging provides practical sampling, image coverage, and spatial resolution, attributes that may be advantageous over MT T1-weighted spin-echo techniques.

Multifocal varicella-zoster virus leukoencephalitis in a patient with AIDS: MR findings.

We describe a patient with AIDS who presented with an acute encephalitis caused by infection with varicella-zoster virus. The hemorrhagic, necrotizing encephalitis had an unusual MR appearance, with innumerable discrete, small, targetlike lesions in the right cerebral hemisphere, which were coalescent in the posterior temporal, parietal, and occipital regions. Of the several known disease patterns of varicella-zoster viral infection in the CNS, this histopathologic pattern of multifocal leukoencephalitis is rare. It is important to recognize, as effective antiviral drug treatments are available.

Ectopic extraspinal meningioma: CT and MR appearance.

We report a case of an ectopic, extraspinal meningioma that appeared as a midline interscapular mass in a 13-year-old girl. The tumor involved the T-2 and T-3 spinous processes, but was dorsal to the lamina and was entirely extrinsic to the spinal canal. Large amounts of tumoral calcification and reactive hyperostosis were present, radiologically mimicking an osteogenic sarcoma.

Analysis of magnetization transfer effects on T1-weighted spin-echo scans using a simple tissue phantom simulating gadolinium-enhanced brain lesions.

The purpose of this study was to analyze the effect of several magnetization transfer (MT) pulse and T1-weighted spin-echo (SE) sequence parameters on lesion-to-background contrast, using a simple tissue phantom emulating the T1 relaxation and MT properties of gadolinium-enhanced brain lesions. Eggbeaters (Nabisco Inc., East Hanover, NJ) liquid egg product was doped with gadolinium in six concentrations from .0 to 1.0 mmol and cooked. The gadolinium-doped egg phantom and normal volunteer brains were studied using an SE sequence with TE = 20 msec and high power, pulsed, off-resonance MT saturation. The effects of MT pulse frequency offset (1,000-6,000 Hz), sequence repetition time (TR = 500-1,000 msec, with MT power held constant), and slice-select flip angle (60-120 degrees) on the magnetization transfer ratio (MTR) and the simulated lesion-to-background contrast were determined at the different "intralesion" gadolinium concentrations. The MTR and lesion-to-background contrast of all materials were greatest at narrow MT pulse frequency offsets. There was in inverse relationship between gadolinium concentration and MTR and a positive correlation between the gadolinium concentration and lesion-to-background (L/B) contrast, a weak negative correlation between slice-select flip angle and L/B, and a negative correlation between TR and L/B. The relaxation properties and MT behavior of the egg phantom are close to that expected for enhancing brain lesions, allowing a rigorous analysis of several variables affecting lesion-to-background contrast for high MT power, T1-weighted SE sequences.

Magnetization transfer effects on T1-weighted three-dimensional gradient-echo MR images of a phantom simulating enhancing brain lesions.

PURPOSE: To develop a simple tissue phantom to study the effects of various imaging parameters and gadolinium concentrations on magnetization transfer (MT) and lesion-to-background ratios. METHODS: A commercial egg product was doped with gadolinium in concentrations of 0.0 to 1.0 mmol/L and cooked. The T1 and T2 values were determined for the phantom materials and for the white and gray matter of a healthy volunteer subject. The gadolinium-doped egg phantom and human brain were studied using a short-repetition-time three-dimensional gradient-echo MT sequence with various effective MT powers, frequency offsets, and section-select flip angles. The normalized signal intensities, MT ratios (MTRs), and simulated lesion-to-background normal white matter contrast ratios were determined for a variety of experimental conditions. RESULTS: The MTR and lesion-to-background contrast ratios for all materials were greatest at the highest effective MT power (270 Hz, root-mean-square of amplitude) and the narrowest MT pulse frequency offset (1000 Hz). There was an inverse relationship between gadolinium concentration and MTR, and a positive relationship between the gadolinium concentration and lesion-to-background contrast. MTR was greatest at low flip angles, where there was little T1 weighting. The simulated lesion-to-background contrast showed a complex, gadolinium concentration-dependent relationship with section excitation flip angle. CONCLUSIONS: The tissue phantom has relaxation properties and MT behavior close to that expected for enhancing brain lesions, allowing a rigorous analysis of simulated lesion-to-background contrast for high MT power, short-repetition-time, three-dimensional gradient-echo sequences.

Cerebral white matter: technical development and clinical applications of effective magnetization transfer (MT) power concepts for high-power, thin-section, quantitative MT examinations.

PURPOSE: To evaluate white matter disorders with magnetization transfer (MT) techniques. MATERIALS AND METHODS: In 46 healthy volunteers and 46 clinical patients, MT Z spectra were obtained with various continuous-wave-equivalent MT powers (B1CW) and frequency offsets. RESULTS: With B1CW of 270 Hz and 4,000-Hz frequency offset, the MT ratio of normal callosal white matter was 59.2% +/- 1.5 (standard deviation), with less than 5% contribution from direct saturation and spin locking. A small statistically significant (P < .01) regional variation in normal white matter was seen. Plaques in MS patients had a broad (or wide) range of MT ratios; normal appearing white matter had a slightly reduced MT ratio. Vasogenic edema had a minimal effect on MT ratio, and radiation necrosis showed prominent reductions in MT ratio. CONCLUSION: High MT power techniques can expand the dynamic range of MT ratios, maintain a relatively pure MT effect, and be used effectively in MT imaging to evaluate white matter disorders.

Leptomeningeal and calvarial sarcoidosis: CT and MR appearance.

We report an unusual case of biopsy-proven combined leptomeningeal and calvarial sarcoidosis, as seen on CT and MRI. A solitary large thick plaque was present in the left hemisphere, with overlying bony infiltration and erosion and associated abundant vasogenic edema in the brain. The lytic lesion was visible on Scout digital radiography for CT slice positioning. The typical manifestations of CNS sarcoidosis, i.e., chronic leptomeningitis in the basilar cisterns and hypothalamic regions, were absent.

Trilateral retinoblastoma: two variations.

Two cases of trilateral retinoblastoma (a syndrome of midline, undifferentiated, intracranial tumor in a child with hereditary, bilateral ocular retinoblastoma) are described, one with a unique location of the intracranial tumor, and the other with an unusual temporal course of disease.

Use of magnetization transfer for improved contrast on gradient-echo MR images of the cervical spine.

PURPOSE: To evaluate whether magnetization transfer (MT) can improve image contrast on gradient-recalled echo (GRE) magnetic resonance (MR) images of the cervical spine. MATERIALS AND METHODS: Sagittal and axial two-dimensional conventional GRE and MT GRE images were obtained in 103 patients with degenerative disk disease or intrinsic cord lesions. The contrast-to-noise ratios (C/Ns) for the cervical spinal cord and cerebrospinal fluid (CSF) were compared for images obtained at various MT power level and section-select flip angle combinations. Axial three-dimensional GRE images were also obtained with application of MT and C/N evaluated in 10 additional patients. RESULTS: Tailored two-dimensional MT GRE images, obtained with a moderate MT power level and a section-select flip angle similar to the Ernst angle for CSF, provided an average of 2.2-2.4-fold improvement in spinal cord-CSF C/N than conventional GRE images (P < .001). CONCLUSION: The MT GRE images demonstrated superior delineation of disk herniations, foraminal stenosis, and intrinsic cord lesions over conventional GRE and T2-weighted spin-echo images in clinical cervical spine examinations.

Experimental confirmation of phase encoding of instantaneous derivatives of position.

Previous theoretical reports described the dependence of interpretation of the observed phase of the NMR signal on the time origin(s) of moment calculations and position's Taylor series expansion. This work provides experimental confirmation of predictions derived from that theory. For accelerative motion, experimental phase-encoded velocity measurements give instantaneous values at a time corresponding to the origin used for waveform moment calculations. For laminar flow, experimental intensity profiles agree well with theoretical simulations; new findings extend amplitude and spatial distributions of oblique flow profiles beyond previous descriptions. Experiments using sequences with controlled position of the time origins for phase and read axes show that displacement and motion artifacts are reduced when they're coincident (pulsed flow, nongated acquisitions), and virtually eliminated when combined with gating. Potentially significant clinical consequences of coincident and noncoincident time origins are demonstrated in human head MIP MRA images. These results have fundamental implications in waveform design.

Improved contrast of enhancing brain lesions on postgadolinium, T1-weighted spin-echo images with use of magnetization transfer.

PURPOSE: To prove that the contrast of enhancing brain lesions on post-gadolinium T1-weighted spin-echo (SE) images can be statistically significantly improved with magnetization-transfer (MT) indirect saturation. MATERIALS AND METHODS: The contrast-to-noise ratios (C/Ns) of 201 enhancing brain lesions in 110 patients were compared on conventional and MT T1-weighted SE images obtained at 1.5 T after injection of 0.05-0.10 mmol/kg gadopentetate dimeglumine or gadodiamide. RESULTS: The MT T1-weighted SE images showed a 37% reduction in signal intensity of background white matter and thereby provided a 108% improvement in the C/N of enhancing brain lesions over the conventional T1-weighted SE images (P < .001). CONCLUSION: The C/Ns obtained with single-dose gadolinium and the MT T1-weighted SE technique were twice those obtained with the conventional technique and are at least equivalent to reported values obtained with triple-dose gadolinium and conventional T1-weighted SE images.

Deceptively normal MR in early infantile Krabbe disease.

The authors present two cases of 5-month-old children with early infantile Krabbe disease studied by CT and MR. Both infants had characteristic CT scans for the disease consisting of symmetric hyperdensity involving the cerebellum, thalami, caudate, corona radiata, and brain stem. One of the infants had a deceptively normal initial MR examination, with dramatic progression of the white-matter disease over the following 4 months.

Varied microcirculation of pituitary adenomas at rapid, dynamic, contrast-enhanced MR imaging.

PURPOSE: Rapid, dynamic, contrast material-enhanced magnetic resonance imaging was performed to evaluate the early enhancement patterns of normal pituitary structures, macroadenomas, and microadenomas. MATERIALS AND METHODS: A 1.5-T imager with a circularly polarized head coil was used on 40 patients referred for investigation of endocrinopathy, of neurologic deficit, or for follow-up of a previously documented pituitary tumor. RESULTS: The technique provided a temporal resolution of one image per 1.25 seconds, allowing discrimination of primary arterial and secondary portal circulation enhancement phases of pituitary structures and tumors. Arterial-phase enhancement of 16 macroadenomas was observed, suggesting a primary arterial blood supply to these lesions. Five microadenomas showed minimal enhancement in the secondary portal circulation phase. A brief temporal phase was also captured, in which cavernous sinus invasion by tumor was visualized as a "filling defect" within the gadolinium-laden laterosellar venous spaces. CONCLUSION: The technique reveals the microcirculatory dynamics associated with pituitary adenomas and suggests a dominant arterial blood supply for macroadenomas. It can supplement routine spin-echo imaging for determination of cavernous sinus invasion. Limitations related to section positioning, resolution, and signal-to-noise ratio exist.

Menkes kinky hair disease: characteristic MR angiographic findings.

We report two cases of Menkes kinky hair disease in which MR and MR angiography were performed. The clinical and imaging features are reviewed. MR demonstrated characteristic cerebrovascular tortuousity and thus may be a valuable aid in diagnosis and follow-up.

Evaluation of experimental early acute cerebral ischemia before the development of edema: use of dynamic, contrast-enhanced and diffusion-weighted MR scanning.

The ability of dynamic, contrast-enhanced, magnetic susceptibility-weighted scanning to delineate early experimental acute cerebral infarction was compared with that of heavily T2-weighted and diffusion-weighted spin echo scanning. Spontaneously hypertensive rats, which had undergone right middle cerebral artery occlusion, were studied from 15 min to 3 h post ligation on a 1.5-T clinical whole-body imager. In contrast to the diffusion- and T2-weighted spin echo scans, the dynamic, contrast-enhanced technique clearly and consistently delineated the nonperfused regions as early as 15 min post ligation.