Gadolinium-enhanced magnetization transfer contrast imaging of intracranial tumors.

The magnetization transfer contrast (MTC) technique was used in low-field-strength (0.1 T) magnetic resonance (MR) imaging of 28 patients with intracranial tumors. MTC images were generated with an off-resonance, low-power radio-frequency pulse applied during the interpulse delay period of a gradient-echo partial-saturation sequence (TR msec/TE msec = 200/20). Images in the presence and absence of the MTC pulse were concurrently acquired before and after injection of gadopentetate dimeglumine at a dose of 0.1 mmol/kg. The contrast agent enhanced 27 of 28 tumors. Application of the MTC pulse improved the contrast-to-noise ratio (C/N) between tumor and normal white matter in 26 of 28 cases on the preinjection images and in 25 of 28 cases on the postinjection images. On the gadolinium-enhanced images, the mean C/N was 2.6 +/- 1.7 without the MTC pulse and 3.2 +/- 1.9 with the MTC pulse. The greatest contrast improvement with the MTC technique was obtained in tumors showing the strongest paramagnetic enhancement. The results indicate that MTC can improve contrast between normal brain and some intracranial neoplasms. The use of gadopentetate dimeglumine generally intensified this effect.     

Depiction of intracranial vessels with MRA: utility of magnetization transfer saturation and gadolinium.

PURPOSE: The purpose of this work was to quantitate the individual and combined effects of magnetization transfer (MT) saturation and gadolinium (Gd) on the visualization of intracranial vessels with MR angiography (MRA). METHOD: Thirty-five subjects underwent two three-dimensional time-of-flight MRA sequences without and with MT and/or Gd. There were 14 MR angiograms without Gd or MT, 18 with MT only, 17 with Gd only, and 21 with both Gd and MT. On a projection image, a region of interest was drawn to delineate the arteries in the middle cerebral artery territory. The total area of blood vessels in the region of interest was calculated for each MR angiogram. Mean vessel areas for the four types of MRA were compared with analysis of variance. RESULTS: MRA with either MT or Gd alone showed significantly more vessel area than MRA without either (p < 0.05). MRA with MT alone and MRA with Gd alone were not different from each other (p = 0.29). The improvement in vessel area measured by using MT and Gd together was significantly more than expected from the cumulative improvement of adding each alone (p < 0.05). CONCLUSION: Combining MT and Gd synergistically improved the visualization of intracranial vessels on MRA.     

Single-dose gadolinium with magnetization transfer versus triple-dose gadolinium in the MR detection of multiple sclerosis lesions.

PURPOSETo compare the efficacy of single-dose gadolinium with magnetization transfer contrast (MTC) with that of triple-dose gadolinium in detecting enhancing multiple sclerosis lesions.METHODSTwenty-one patients with multiple sclerosis were examined with MR imaging first with 0.1 mmol/kg gadolinium (single dose) and then, after 24 to 72 hours, with 0.3 mmol/kg gadolinium (triple dose). T2-weighted fast spin-echo and T1-weighted spin-echo MR images with and without MTC were obtained before contrast administration followed by either T1-weighted spin-echo images with MTC (single dose) or conventional T1-weighted spin-echo images (triple dose), starting 5, 17, and 29 minutes after contrast administration. All images were evaluated in a blinded fashion and scored in random order by two readers. Outcome parameters included number of enhancing lesions, number of active MR examinations (those containing at least one enhancing lesion), contrast ratio (signal intensity of enhancing lesion divided by signal intensity of normal-appearing white matter), and size of enhancing lesions.RESULTSEighty-one percent more enhancing lesions and 49% more active MR examinations were detected when a triple dose of gadolinium was used as compared with a single dose. The level of agreement between readers as to the number of enhancing lesions was significantly higher for triple-dose than for single-dose gadolinium. With triple-dose gadolinium, contrast ratios and areas of enhancement increased by 10% and 33%, respectively. Delayed imaging increased the size of the lesion by 11% on single-dose MTC images and by 18% on triple-dose images.CONCLUSIONTriple-dose gadolinium is more effective (higher sensitivity and interobserver agreement) than single-dose gadolinium in combination with MTC in detecting enhancing multiple sclerosis lesions.     

Hepatic tumors: Magnetization transfer MR imaging with gadolinium enhancement

Thirty patients with 15 hepatocellular carcinomas, 10 metastases, four hemangiomas, and one cholangiocarcinoma underwent magnetic resonance imaging at 1.5 T with T1-weighted, T2- weighted spin-echo (SE) images, gradient-echo (GRE) magnetization transfer (MT) images, and gadolinium-enhanced T1-weighted SE and MT- GRE images. The MT effect and lesion-liver contrast-to-noise ratio (C/N) were calculated and visual assessment (qualitative analysis) performed for unenhanced and enhanced MT-GRE images and enhanced Tl-weighted SE images. The C/N values for hepatic adenocarcinomas (seven metastases and one cholangiocarcinoma) and hemangiomas were larger for enhanced MT-GRE images (adenocarcinoma, 8.4 ± 2.3 [P < 0.01); hemangioma, 24 ± 2.1 [P < 0.05]) than for enhanced GRE images (5.0 ± 1.9 and 18 ± 2.7, respectively). These enhancing tumors had the highest scores in the qualitative analysis. Enhanced MT-GRE images showed no advantage for depiction of hepatocellular carcinomas relative to the other images.     

Determination of magnetization transfer contrast in tissue: an MR imaging study of brain tumors.

OBJECTIVE. In this study, the magnetization transfer contrast (MTC) on MR images of several brain tumors and the correlation between MTC and tumors' histologic features were investigated. MTC depends on the extent of magnetization transfer, or cross-relaxation, from tissue water protons to macromolecular protons. On the basis of the known increase of the cross-relaxation rate with increasing molecular weight of protein in protein solutions, the hypothesis that changes in MTC correlate directly with the macromolecular composition of various tumors was tested. SUBJECTS AND METHODS. Preoperative MR images were obtained with a 0.1-T MR system in 40 patients with brain tumors. MTC was correlated with the histologic features and the dry weight of the tumors. The tumors studied included astrocytomas (10), acoustic schwannomas (three), meningiomas (12), pituitary adenomas (10), craniopharyngiomas (two), and hemangioblastomas (three). RESULTS. MTC was 0.43 in normal white matter and 0.42 in normal gray matter, and varied from 0.11 to 0.37 in the tumors. The mean MTC in astrocytomas (0.21 +/- 0.09) was smaller than the mean MTC in the gray matter (p = .0001) or in the other solid tumors (0.34 +/- 0.07 to 0.37 +/- 0.09, p < .002). MTC was larger in high-grade than in low-grade astrocytomas (0.28 +/- 0.05 vs 0.14 +/- 0.04, p = .0005). In meningiomas, MTC correlated with the collagen content of the tumor tissue (r = .95, p = .01). The differences in contents of solids between the solid tumor groups were not significant (p > or = .1, NS). CONCLUSION. When the previously demonstrated correlations between solid content and 1/T1 of the types of tumors studied are taken into consideration, the present results suggest a larger relative contribution from hydrodynamic vs cross-relaxation effects in astrocytomas than in benign tumors or in gray matter. The twofold difference in MTC between low- and high-grade astrocytomas probably reflects the amount of nuclear material in the tumor cells. Collagen content determined the differences in MTC among meningiomas. These results indicate that the major determinant of differences in MTC within these tumor groups is the high-molecular-weight tissue macromolecules, suggesting higher specificity for MTC than for T1 in discriminating between tissues on MR images.     

Cervical spondylosis: three-dimensional gradient-echo MR with magnetization transfer.

PURPOSETo compare a three-dimensional Fourier transform (3DFT) gradient-echo pulse sequence with magnetization transfer at a short echo time against standard 3DFT gradient-echo technique in the evaluation of cervical spondylosis, specifically addressing the effects of motion and susceptibility artifacts on the dimensions of the neural foramina and contrast at the cerebrospinal fluid (CSF)-spinal cord interface.METHODSTen patients with clinically suspected cervical spondylosis were examined with axial MR imaging using both our standard 3DFT gradient-echo sequence and a 3DFT gradient-echo sequence with a short echo time plus magnetization transfer. Two neuroradiologists measured the transverse dimensions of 22 diseased neural foramina and graded the contrast at the CSF-spinal cord interface.RESULTSSixteen of 22 affected neural foramina were larger in the transverse dimension when the magnetization transfer technique was used than when the standard 3DFT gradient-echo sequence was used. In 9 of 10 patients superior contrast was seen at the CSF-spinal cord interface on images obtained with the magnetization transfer technique.CONCLUSIONSIn the cervical spine, 3DFT gradient-echo imaging with magnetization transfer improves contrast and sharpness of the CSF-spinal cord interface at short echo times. This results in less exaggeration of the neural foraminal stenosis as compared with that seen with standard 3DFT gradient-echo techniques owing to the diminished effects of motion and susceptibility artifacts.     

Tissue characterization of intracranial tumors by magnetization transfer and spin-lattice relaxation parameters in vivo

T1s and magnetization transfer (MT) parameters of 36 intracranial tumors were determined in vivo at 0.1 T to assess their use in tissue characterization. The mobile water relaxation times (T1_w) did not differ between tumor groups, whereas the T1s, the apparent MT relaxation times (T1_a), and the parameters MT contrast (MTC) differed significantly between several tumor types. The MT rates (R_wm) demonstrated the most significant differences; R_wm values could reliably separate high grade and low grade gliomas. T1_ws of the tumors were commonly in the same range as that of normal gray matter, whereas other parameters differed from those of normal brain. The results indicate that MT rates are superior to other parameters in the characterization of intracranial tumors and may be also useful clinically in the grading of gliomas.     

Pulsed magnetization transfer spin-echo MR imaging

Cross relaxation between macromolecular protons and water protons is known to be important in biologic tissue. In magnetic resonance (MR) imaging sequences, selective saturation of the characteristically short T2 macromolecular proton pool can produce contrast called magnetization transfer contrast, based on the cross-relaxation process. Selective saturation can be achieved with continuous wave irradiation several kilohertz off resonance or short, intense 0° pulses on resonance. The authors analyze 0° binomial pulses for T2 selective saturation, present design guidelines, and demonstrate the use of these pulses in spin-echo imaging sequences in healthy volunteers and patients. Using the phenomenologic Bloch equations modified for two-site exchange, the authors derive the analytic expressions for water proton relaxation under periodic pulsed saturation of the macromolecular protons. This relaxation is shown to be monoexpo-nential, with a rate constant dependent on the saturation pulse repetition rate and the individual and cross-relaxation rates.     

Contrast-enhanced magnetization transfer MR of the brain: importance of precontrast images.

PURPOSETo determine the importance of obtaining precontrast T1-weighted magnetization transfer (MT) MR images for better interpretation contrast-enhanced T1-weighted MT images.METHODSOne hundred fifty-five patients referred for MR imaging of the brain were examined prospectively with noncontrast T1-weighted imaging, noncontrast T1-weighted imaging with MT, contrast-enhanced T1-weighted imaging, and contrast-enhanced T1-weighted imaging with MT. In the patients who had abnormally increased signal intensity on postcontrast images (with or without MT), the four imaging sequences were evaluated with regard to number of lesions and lesional signal intensity. For each of the sequences, two experienced neuroradiologists subjectively graded the lesions on a scale of 1 to 4 (4 being the most conspicuous) with regard to abnormally increased signal intensity.RESULTSTwenty-two of the 155 patients had increased signal intensity on one or more of the postcontrast sequences. Eight of these 22 patients had increased signal intensity of one or more lesions on images without MT. All these lesions were seen better on images obtained with MT. An additional six of the 22 patients had increased signal intensity of one or more lesions on images obtained with MT that was not detected on images obtained without MT. Eight of the 22 patients had no high signal intensity on noncontrast images with or without MT. One of the eight had increased number and conspicuity of lesions on postcontrast MT images.CONCLUSIONSA significant number of patients had increased signal intensity on noncontrast T1-weighted images with MT that was not seen on noncontrast T1-weighted images without MT. This high signal intensity was also visible on postcontrast MT images, and would have been mistaken for pathologic enhancement if noncontrast MT images had not been available for comparison.     

Intracranial stenoocclusive disease: MR angiography with magnetization transfer and variable flip angle.

PURPOSETo assess time-of-flight MR angiography that uses magnetization transfer contrast (MTC) pulses, tilted optimized nonsaturating excitation (TONE), and a 256 x 512 image matrix for the detection of small intracranial arteries and for the detection and quantification of intracranial arterial stenoocclusive disease.METHODSTo assess anatomic sensitivity, six interpreters, in a blinded fashion, reviewed the MTC/TONE MR angiograms and selective intraarterial angiograms obtained in 70 patients within a mean interval of 5.5 days (SD, 1.5). In addition, all intracranial angiograms were evaluated with regard to presence and degree of arterial stenosis and anatomic variants.RESULTSInterobserver correlations for determining vessel length were comparably high for both methods. A strong correlation was found between measurements obtained on MR angiograms and those obtained on intraarterial angiograms. The mean vascular length averaged across all arteries was 34.8 mm (SD, 28.1) on MR angiograms and 53.2 mm (SD, 36.8) on intraarterial angiograms. Forty-one stenoses and occlusions and 30 anatomic variants were identified with intraarterial angiography. All arterial variants and 100% of occluded vessels were graded correctly. Moreover, 80% of stenoses greater than 70% and 88% of stenoses less than 70% were quantified correctly at MR angiography. Specificity for identifying stenotic disease was 99%.CONCLUSIONDespite inferior display of vessel length, MTC/TONE MR angiography with increased spatial resolution was able to show the vast majority of high grade lesions visible at selective intraarterial angiography and may suffice for clinical decision making in many patients.     

MR magnetization transfer measurements in temporal lobe epilepsy: a preliminary study.

MR magnetization transfer ratio was measured in both hippocampi of three patients with temporal lobe epilepsy, and in two control subjects. The magnetization transfer ratio in each section was significantly lower on the affected side than on the contralateral side and in control subjects. Magnetization transfer ratio measurements are relatively fast and precise, this preliminary study shows that they may provide useful presurgical information.     

Lysolecithin-induced demyelination in primates: preliminary in vivo study with MR and magnetization transfer.

PURPOSETo study bystander demyelination in multiple sclerosis with an experimental in vivo model of toxic demyelination.METHODSToxic demyelinating lesions were created in two monkeys by injection of lysophosphatidylcholine in the centrum semiovale. Follow-up was done clinically and with serial MR studies, including T2-weighted and gadolinium-enhanced T1-weighted images and measurement of magnetization transfer ratio, until the animals were killed at days 14 and 34, respectively. Light and electron microscopy analysis was compared with MR data.RESULTSInterval measurement of magnetization transfer ratio during the course of the experiment revealed a maximum decrease at day 7 to day 8, associated with the greatest clinical manifestations. The lowest values of magnetization transfer ratio correlated with histopathologic findings of myelin and axon destruction. Magnetization transfer ratio measurements appear to be sensitive to macromolecular destruction and specifically to membrane disorganization. At no time was gadolinium enhancement observed in this model of toxic demyelination.CONCLUSIONPreliminary results of this study indicated that magnetization transfer is a good technique to follow in vivo matrix destruction in brain parenchyma lesions. The results suggest also that phases of toxic demyelination in multiple sclerosis might not show gadolinium enhancement. Differentiation between demyelinating activity and associated inflammation in multiple sclerosis lesions should be considered in further in vivo work.     

Improved time-of-flight MR angiography of the brain with magnetization transfer contrast.

The authors hypothesized that magnetization transfer contrast (MTC) could be used to improve flow contrast in time-of-flight (TOF) magnetic resonance (MR) angiography. Two- and three-dimensional flow-compensated gradient-echo images were obtained with and without MTC. MTC images were obtained by applying low-power radio-frequency (RF) radiation with a frequency offset from the bulk "free" water resonance frequency before the excitation RF pulse. The signal intensity of stationary tissue decreased as the power applied for the MTC pulse was increased. A smaller decrease occurred in venous signal intensity as measured in the superior sagittal sinus, and less change was seen in the arterial signal intensity as measured in the middle cerebral artery. Cerebrospinal fluid showed no MTC effect. The use of MTC improved small-vessel depiction on maximum-intensity projection images. The authors conclude that use of MTC can substantially enhance the quality of TOF MR angiography of the brain.     

Three-dimensional MR imaging and display of intracranial disease: Improvements with the MP-RAGE sequence and gadolinium

Three-dimensional (3D) image rendering was performed in 14 patients who had undergone magnetic resonance (MR) imaging for focal brain lesions. The MR study included the magnetization-prepared rapid gradient-echo (MP-RAGE) sequence with 64 or 128 partitions. Resultant contiguous sections 2.5 or 1.25 mm thick, respectively, were obtained. Images were acquired before and after administration of gadopen-letate dimeglumine. Resultant 3D data sets were processed on a commercially available workstation. Correlative surgical observation was performed in four cases. All data sets were successfully processed into 3D images. The precontrast images proved superior to gadolinium-enhanced images for brain surface rendering. Postcontrast images proved superior for reconstruction of tumors and vascular structures. The 64-partition data set proved sufficient for all postprocessing. Coronal orientation was preferred to sagittal orientation for surface rendering because it provided optimal orthogonal orientation of sulcal and gyral brain surface features. Three-dimensional rendition allowed easy superposition of lesion, brain, vessels, and scalp features-all useful for surgical planning. The central sulcus was easily recognized in the mid-line partitions and traced mediolaterally for projection on the cortical surface. MP-RAGE provides a 3D data set that can be obtained in just over 3 minutes, from which clinically useful 3D renderings are possible. The rapidity of acquisition and capability for 3D rendering provides additional clinical utility.     

Parotid masses: prediction of malignancy using magnetization transfer and MR imaging findings

OBJECTIVE: We determined the most accurate criteria for predicting malignancy of masses in the parotid gland using magnetization transfer ratios. SUBJECTS AND METHODS: Lesion-to-muscle magnetization transfer ratios obtained with a spoiled gradient-recalled acquisition in a steady state sequence with a 1-kHz off-resonance pulse were measured in 72 parotid masses (52 benign lesions, 20 malignant tumors). Various MR imaging findings and lesion-to-muscle magnetization transfer ratios were simultaneously assessed using a logistic model to determine the useful factors for predicting malignancy. We also studied the clinical usage of magnetization transfer ratios. RESULTS: Of the MR imaging findings, poorly defined margins showed the highest accuracy, 81%, with 60% sensitivity and 88% specificity. Of the lesion-to-muscle magnetization transfer ratios, a ratio of greater than 0.71 was most accurate (85%), with 90% sensitivity and 83% specificity. All four recurrent tumors and 10 (91%) of 11 secondary tumors were correctly diagnosed using the magnetization transfer ratio analysis. The logistic model revealed that the margin characteristics (p = 0.084) and lesion-to-muscle magnetization transfer ratios (p < 0.001) were statistically significant predictors for malignancy. A combined criteria of poorly defined margins and a lesion-to-muscle magnetization transfer ratio of greater than 0.71 raised the accuracy to 86% and specificity to 96%, but the sensitivity decreased to 60%. CONCLUSION: A combination of MR imaging findings and lesion-to-muscle magnetization transfer ratios was the most accurate predictor of malignancy.     

颅内孤立性纤维瘤的MRI表现

目的:探讨颅内孤立性纤维瘤(I-SFT)的MRI表现。方法:回顾性分析8例经手术病理证实的I-SFT的MRI及病理学资料。结果:肿瘤发生在幕下2例,幕上3例(其中侧脑室内1例),跨越幕上及幕下2例,鞍区1例。1例鞍区肿瘤在T1WI、T2WI上呈均匀等信号,其余7例信号不均,T1WI、T2WI上以等、稍高信号为主,其中5例T2WI见小斑片状低信号区,3例见囊变灶,5例病灶内可见粗大流空血管影。MRI增强扫描示8例均明显强化;鞍区肿瘤强化均匀,其余7例强化不均;5例T2WI低信号区明显强化,3例囊变区未见强化,2例可见脑膜尾征。除侧脑室内1例周围脑实质水肿明显外,其余7例无或轻度水肿。病理显示8例均见丰富的小梭形细胞;免疫组化显示CD34(~),CD99(+),Bcl(+),Vimentin(+),EMA(-)。结论:I-SFT的MRI表现有一定的特点,当脑膜肿瘤呈等、较高信号,增强呈明显强化,其内出现粗大流空血管、T2WI低信号区时,可考虑该病诊断,但其确诊仍需依靠组织病理学。