Cerebral infarction: effects of dose and magnetization transfer saturation at gadolinium-enhanced MR imaging

Utility of Contrast-Enhanced T2 FLAIR for Imaging Brain Metastases Using a Half-dose High-Relaxivity Contrast Agent

BACKGROUND AND PURPOSE

Efficient detection of metastases is important for patient' treatment. This prospective study was to explore the clinical value of contrast-enhanced T2 FLAIR in imaging brain metastases using half-dose gadobenate dimeglumine.

MATERIALS AND METHODS

In vitro signal intensity of various gadolinium concentrations was explored by spin-echo T1-weighted imaging and T2 FLAIR. Then, 46 patients with lung cancer underwent nonenhanced T2 FLAIR before administration of half-dose gadobenate dimeglumine and 3 consecutive contrast-enhanced T2 FLAIR sequences followed by 1 spin-echo T1WI after administration of half-dose gadobenate dimeglumine. After an additional dose of 0.05 mmol/kg, 3D brain volume imaging was performed. All brain metastases were classified as follows: solid-enhancing, ≥ 5 mm (group A); ring-enhancing, ≥ 5 mm (group B); and lesion diameter of <5 mm (group C). The contrast ratio of the lesions on 3 consecutive phases of contrast-enhanced T2 FLAIR was measured, and the percentage increase of contrast-enhanced T2 FLAIR among the 3 groups was compared.

RESULTS

In vitro, the maximal signal intensity was achieved in T2 FLAIR at one-eighth to one-half of the contrast concentration needed for maximal signal intensity in T1WI. In vivo, the mean contrast ratio values of metastases on contrast-enhanced T2 FLAIR for the 3 consecutive phases ranged from 63.64% to 83.05%. The percentage increase (PI) values of contrast-enhanced T2 FLAIR were as follows: PI_A < PI_B (P = .001) and PI_A < PI_C (P < .001). The degree of enhancement of brain metastases on contrast-enhanced T2 FLAIR was lower than on 3D brain volume imaging (P < .001) in group A, and higher than on 3D brain volume imaging (P < .001) in group C.

CONCLUSIONS

Small or ring-enhancing metastases can be better visualized on delayed contrast-enhanced T2 FLAIR using a half-dose high-relaxivity contrast agent.

Advocating the Development of Next-Generation High-Relaxivity Gadolinium Chelates for Clinical Magnetic Resonance

The question of improved relaxivity, and potential efficacy therein, for a next-generation of magnetic resonance gadolinium chelates with extracellular distribution and renal excretion, which could also be viewed from the perspective of dose, is addressed on the basis of historical development, animal experimentation, and human trials. There was no systematic evaluation that preceded the choice of 0.1 mmol/kg as the standard dose for human imaging with the gadolinium chelates. In part, this dose was chosen owing to bloodwork abnormalities seen in phase I and phase II studies. Animal investigations and early clinical trials demonstrated improved lesion detectability at higher doses in the brain, liver, and heart. By designing an agent with substantially improved relaxivity, higher enhancement equivalent to that provided with the conventional gadolinium agents at high dose could be achieved, translating to improved diagnosis and, thus, clinical care. Implicit in the development of such high-relaxivity agents would be stability equivalent to or exceeding that of the currently approved macrocyclic agents, given current concern regarding dechelation and gadolinium deposition in the brain, skin, and bone with the linear agents that were initially approved. Development of such next-generation agents with a substantial improvement in relaxivity, in comparison with the current group of approved agents, with a 2-fold increase likely achievable, could lead to improved lesion enhancement, characterization, diagnosis, and, thus, clinical efficacy.

Contrast-enhanced FLAIR imaging in combination with pre- and postcontrast magnetization transfer T1-weighted imaging: Usefulness in the evaluation of brain metastases

PURPOSE

To assess whether the use of postcontrast fluid-attenuated inversion recovery (FLAIR) imaging in combination with pre- and postcontrast magnetization transfer (MT) T1-weighted imaging (T1WI) can increase diagnostic confidence in the evaluation of brain metastases.

MATERIALS AND METHODS

Brain MR images from 41 patients with suspected brain metastases were reviewed. Two radiologists viewed pre- and postcontrast MT-T1W images for the presence of metastatic tumors and rated the possible enhanced lesions using a five-point confidence scale (session 1). The postcontrast FLAIR images were then viewed together with pre- and postcontrast MT-T1W images, and the presence of metastasis was rated again (session 2).

RESULTS

A total of 240 possible enhanced lesions were detected in session 1. Judging by follow-up MR examinations, 196 were considered to be nonmetastatic findings and 44 were determined to be metastasis. In session 2 the confidence rating for nonmetastasis increased significantly in the subset of nonmetastatic findings (P < 0.001), and the confidence rating for metastasis increased significantly in the subset of metastases (P < 0.05).

CONCLUSION

The addition of postcontrast FLAIR imaging to pre- and postcontrast MT-T1WI improves diagnostic confidence in evaluation of brain metastases.

Brain Tumors: Full- and Half-Dose Contrast-enhanced MR Imaging at 3.0 T Compared with 1.5 T—Initial Experience

PURPOSE

To prospectively and intraindividually compare the effect of magnetic resonance (MR) imaging at a higher magnetic field strength (3.0 T) on contrast-to-noise ratio (CNR) at different doses of a T1-shortening contrast agent in patients with contrast-enhancing brain lesions, with 1.5-T MR imaging as a reference standard.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for all patient and volunteer studies. Twelve patients (six women, six men; mean age, 58 years; range, 29-76 years) with 12 enhancing brain lesions (11 patients with primary brain tumors and one with a solitary cerebral metastasis) underwent contrast material-enhanced MR imaging three times, on three separate days: once at 1.5 T with a full dose of 0.10 mmol/kg gadopentetate dimeglumine, once at 3.0 T with a full dose, and once at 3.0 T with half that dose, 0.05 mmol/kg. The same contrast-enhanced T1-weighted spin-echo images (repetition time msec/echo time msec, 500/12; section thickness, 5 mm; matrix, 256 x 205) were obtained at both 3.0 T and 1.5 T after prior optimization of parameters at 3.0 T. The number and conspicuity of enhancing brain lesions were assessed with blinded clinical image reading. Signal-to-noise ratio and CNR were determined with region of interest analysis of enhancing lesions and normal contralateral white matter. For 3.0 T with half the standard dose and with the full dose, CNR of lesions was intraindividually compared with CNR at 1.5 T with the full dose by using the Wilcoxon matched-pairs signed rank test.

RESULTS

At 3.0 T and full dose, CNR was 2.8-fold higher than that at 1.5 T and full dose (P < .001). At the same time, higher lesion conspicuity at clinical image reading was observed. With only half the standard dose, MR imaging at 3.0 T still yielded higher CNR (1.3-fold higher) than that with full dose at 1.5 T (P < .01).

CONCLUSION

With the same amount of contrast agent, MR imaging at 3.0 T offered a significantly higher CNR of enhancing cerebral lesions, compared with that at 1.5 T; even with the dose reduced by half, CNR was still higher at 3.0 T.

Acute myocardial infarction: tissue characterization with T1rho-weighted MR imaging--initial experience

Acute myocardial injury was evaluated in 21 patients by using a contrast material-enhanced T1rho-weighted cine turbo field-echo magnetic resonance (MR) imaging sequence and a delayed-enhancement sequence. In 12 of 21 patients, conventional T1-weighted contrast-enhanced cine turbo field-echo MR images were also collected for direct comparison with T1rho-weighted images. Delayed-enhancement technique distinctly characterized irreversible injury (percentage enhancement, 588% +/- 344). With T1rho weighting, percentage enhancement of irreversibly injured myocardium was 68% +/- 41, compared with 23% +/- 24 without T1rho weighting (P <.006). The addition of T1rho weighting to contrast-enhanced cine turbo field-echo MR sequences may offer a new contrast enhancement mechanism for characterization of acutely infarcted myocardium.

Infectious meningitis: prospective evaluation with magnetization transfer MRI

The study was performed with the aim of prospectively characterizing infectious meningitis of different aetiology using magnetization transfer (MT) MRI. Spin-echo (SE) T(1), T(2) and pre- and post-contrast T(1) weighted MT images in 100 patients with aetiologically proven meningitis were evaluated for the visibility and enhancement of the meninges on pre- and post-contrast T(1) weighted MT images, respectively. The MT ratio (MTR) was calculated from the thickened meninges in tuberculous meningitis. In addition, the percentage difference in the mean signal intensity (SI) of the meninges and adjacent brain parenchyma was calculated and compared between different groups using 2-tailed student's t-test. T(1) weighted MT images were highly sensitive (96%) in the detection of abnormal meningeal enhancement. Meninges were visible on pre-contrast T(1) weighted MT images only in patients with tuberculous meningitis. The MTR from meninges in tuberculous infection was 19.10+/-1.02, and the percentage difference in the mean SI of the meninges and the adjacent T(2) normal brain parenchyma was significantly higher (p<0.05) in the tuberculous group compared with that in the non-tuberculous group. MT MRI is an important technique for the detection and characterization of infectious meningitis of different aetiology. Visibility of the meninges on pre-contrast T(1) weighted MT images may be considered highly suggestive of tuberculous meningitis.

Comparison of contrast-enhanced magnetization transfer imaging and contrast-enhanced fat saturation T1-weighted imaging in nasopharyngeal carcinoma

OBJECTIVE

The objective of this study was to evaluate the efficacy of contrast-enhanced magnetization transfer (CEMT) imaging in the study of nasopharyngeal carcinoma (NPC).

METHODS

The contrast-to-noise ratio (CNR) of CEMT images was compared with the CNR of contrast-enhanced fat-saturation (CEFS) T1-weighted images in locoregional tumors and adenopathies of 50 patients with pathologically proven NPC.

RESULTS

The CEMT images showed higher CNRs than CEFS images of local nasopharyngeal regions. The mean CNRs of the precontrast T1-weighted, CEFS, and CEMT images were 4.9, 15.4, and 21.2, respectively. There was a statistically significant difference (p < 0.01) in the CNRs of CEFS and CEMT images. In considering images of nodal metastasis, the mean values in these three groups were 0.7, 16.8, and 19.7, respectively, with the difference (p < 0.05) between CEFS and CEMT being statistically significant.

CONCLUSIONS

The CEMT image with a larger CNR is superior to the CEFS image in detecting locoregional NPC. CEMT can be useful in imaging patients with possible small tumors and local recurrences.

Comparative evaluation of magnetization transfer MR imaging and in-vivo proton MR spectroscopy in brain tuberculomas

We have compared and analyzed the value of in vivo proton MR spectroscopy (PMRS) and T1 weighted magnetization transfer (MT) MR imaging in tissue characterization of brain tuberculomas. We studied 33 cases of proven intracranial tuberculomas with in vivo PMRS and T1 weighted MT MR imaging. MT ratios from the rim and core of the tuberculomas were calculated and compared with metabolites seen on PMRS. Final diagnosis of tuberculoma was based on histopathology (n = 26) and/or associated tuberculous meningitis (n = 7) in all the cases. Out of the 33 patients who underwent both PMRS and T1 weighted MT MR imaging, spectroscopy showed only lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm, and 2.80 ppm in 26 cases while lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm and 2.80 ppm along with choline at 3.22 ppm was seen in remaining 7 patients. MT ratios from the core or solid necrosis varied from 21-29% while from the rim or cellular region varied from 16-24%. MT ratios from all the 33 lesions were consistent with tuberculomas while PMRS showed choline along with lipids in 7 predominantly cellular lesions simulating a neoplasm. We conclude that T1 weighted MT MR imaging appears to be more consistent in the tissue characterization of brain tuberculomas.

Characteristics and pitfalls of contrast-enhanced, T1-weighted magnetization transfer images of the brain

RATIONALE AND OBJECTIVES

This study was undertaken to clarify the difference in signal pattern on contrast material-enhanced T1-weighted magnetic resonance (MR) magnetization transfer (MT) images between enhancing and nonenhancing lesions in various intracranial diseases and to determine the necessity of nonenhanced MT images for evaluating lesional contrast enhancement.

MATERIALS AND METHODS

MR images of 116 patients who underwent nonenhanced T1-weighted imaging, nonenhanced MT imaging, and contrast-enhanced MT imaging were reviewed. The increase in signal intensity of lesions relative to normal brain was compared between nonenhanced T1-weighted images and contrast-enhanced MT images. Signal intensity of lesions was compared with that of the striate nucleus and white matter on contrast-enhanced MT images. True enhancement was determined by comparison with nonenhanced MT images.

RESULTS

In all, 143 lesions, including 86 enhancing and 57 nonenhancing lesions, were identified among 63 patients. Almost all (99%) of the enhancing lesions were hyperintense to striate nucleus on contrast-enhanced MT images, and most (>87%) showed moderate to marked signal intensity increase from nonenhanced T1-weighted images to contrast-enhanced MT images. Most (>95%) of the nonenhancing lesions showed mild or no increase in relative signal intensity, and most (75%) were iso- or hypointense to striate nucleus on contrast-enhanced MT images. A few nonenhancing lesions (4%-6%), however, showed increase in signal intensity that was indistinguishable from true enhancement without comparison to non-enhanced MT images.

CONCLUSION

Nonenhanced MT images should be obtained to assess pathologic enhancement accurately.

Optimizing lesion contrast without using contrast agents

The essence of optimizing lesion detection is increasing the signal-to-noise (S/N) for the lesion while decreasing the S/N of the background. Maneuvers which improve one aspect of lesion detection may have a deleterious effect on another. For example, thinner slices decrease partial volume averaging (important for detection of small lesions) but also decrease S/N. Attempts to increase S/N by lowering the bandwidth may increase the TE, decreasing the degree of T1-weighting. Fast spin echo (FSE) generally offers the best T2-weighting for detection of long T2 lesions. However, lesions with short T2s (due to magnetic susceptibility effects) are better detected with gradient echo techniques. Strategies which decrease background S/N include those based on chemical shift differences (ie, spectroscopic techniques like FatSat) and those based on differences in T1 (ie, inversion recovery [IR] techniques like STIR and FLAIR).

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.

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.

Brain: gadolinium-enhanced fast fluid-attenuated inversion-recovery MR imaging

PURPOSE

To determine the clinical utility of gadolinium-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain by comparing results with those at gadolinium-enhanced T1-weighted MR imaging with magnetization transfer (MT) saturation.

MATERIALS AND METHODS

In 105 consecutive patients referred for gadolinium-enhanced brain imaging, FLAIR and T1-weighted MR imaging with MT saturation were performed before and after administration of gadopentetate dimeglumine (0.1 mmol per kilogram of body weight). Pre- and postcontrast images were evaluated to determine the presence of abnormal contrast enhancement and whether enhancement was more conspicuous with the FLAIR or T1-weighted sequences.

RESULTS

Thirty-nine studies showed intracranial contrast enhancement. Postcontrast T1-weighted images with MT saturation showed superior enhancement in 14 studies, whereas postcontrast fast FLAIR images showed superior enhancement in 15 studies. Four cases demonstrated approximately equal contrast enhancement with both sequences. Six cases showed some areas of enhancement better with T1-weighted imaging with MT saturation and other areas better with postcontrast fast FLAIR imaging. Superficial enhancement was typically better seen with postcontrast fast FLAIR imaging.

CONCLUSION

Fast FLAIR images have noticeable T1 contrast making gadolinium-induced enhancement visible. Gadolinium enhancement in lesions that are hyperintense on precontrast FLAIR images, such as intraparenchymal tumors, may be better seen on T1-weighted images than on postcontrast fast FLAIR images. However, postcontrast fast FLAIR images may be useful for detecting superficial abnormalities, such as meningeal disease, because they do not demonstrate contrast enhancement of vessels with slow flow as do T1-weighted images.

Gadoteridol in multiple sclerosis patients. A comparison of single and triple dose with immediate vs. delayed imaging

Enhancement of lesions in multiple sclerosis (MS) has been investigated using standard and high doses of gadolinium. The purposes of this study are to compare the relative merits of single and triple dose as well as examine the merits of delayed triple-dose images in a large group of patients. Thirty-seven patients with multiple sclerosis underwent contrast enhanced brain magnetic resonance imaging (MRI). After noncontrast images, a single dose (0.1 mmol/kg) of gadoteridol was administered. Subsequently, axial T1-weighted images were obtained immediately after administration, and again after a delay of approximately 20 minutes. After an additional 0.2-mmol/kg dose was administered, to provide a total cumulative dose of 0.3 mmol/kg of gadoteridol, immediate and delayed axial T1-weighted image sequences were repeated. The contrast-noise ratio (C/N) was calculated for each identified, enhancing lesion in each series. Furthermore, blinded readings were performed to determine the lesion detection rate. Of the forty definite lesions that underwent all four sequences, triple-dose delayed images exhibited the highest contrast-noise ratio in a significantly larger number of lesions (p < 0.0001). Triple-dose immediate and delayed scans resulted in significantly higher contrast-noise ratios (6.47 and 9.99, respectively) when compared with those of the single dose scans (3.4 for immediate scans and 5.24 for delayed) (p < 0.01). The lesion detection rate was highest for triple dose delayed (95%), followed by triple-dose immediate (83%), single-dose delayed (68%) and finally, single-dose immediate scans (43%). Triple-dose immediate was noted to have a significantly increased (p < 0.0002) lesion detection rate with respect to the standard-dose immediate scans and standard-dose delayed scans (p < 0.02). In four lesions (10% of the total number of lesions), detection occurred only with the triple-dose delayed image sequence. Triple-dose 0.3 mmol/kg gadolinium with delayed imaging resulted in the highest lesion conspicuity and the highest lesion identification rate. There was a trend of progressively increasing detection rates from single-dose immediate scans to triple-dose delayed scans. Triple-dose delayed scans resulted in significantly higher (p < 2 x 10(-8) contrast noise ratios than all other sequences of this study.

Off-resonance experiments and contrast agents to improve magnetic resonance imaging

The effect of off-resonance irradiation on the water proton NMR signal intensity has been investigated as follows: (a) in the presence of a paramagnetic probe like manganese(II); (b) in the presence of bovine serum albumin (BSA) and two gadolinium(III) complexes, Gd-DTPA and Gd-BOPTA; (c) in the presence of cross-linked BSA and the two above-mentioned gadolinium(III) complexes. The experimental data have been rationalized on the basis of the available theoretical models. The effectiveness of the two complexes as contrast agents for MRI has been predicted. It is shown that contrast agents providing comparable longitudinal and transverse relaxation rate enhancements are those of general interest for off-resonance magnetization transfer-MRI.

Gadolinium chelates with weak binding to serum proteins. A new class of high-efficiency, general purpose contrast agents for magnetic resonance imaging

RATIONALE AND OBJECTIVES

The authors assess the effect of weak protein binding on the efficacy of gadolinium chelates as contrast agents for magnetic resonance imaging (MRI).

METHODS

Chelates with no (gadopentetate dimeglumine), weak (gadobenate dimeglumine), and strong (B-21326/7) protein binding were compared by in vitro MRI at 2T (spin echo [SE]: repetition time [TR]/echo time [TE] 350/8 mseconds) on solutions in 0.5 mM bovine serum albumin and in rat whole blood, and by in vivo MRI at 2T on rat models of brain tumors (SE TR/TE 350/10 mseconds) and of focal blood-brain barrier disruption (SE TR/TE 400/15 mseconds) after injection of MPP+. Relaxation rate enhancement in the blood of normal rabbits was measured in vivo after administration of contrast agents using IR-Snapshot FLASH.

RESULTS

Signal intensity enhancement measured in vitro for whole rat blood 0.1 mM in gadobenate was 142% relative to the same concentration of gadopentetate. Peak signal intensity enhancement in brain tumors was 87% +/- 8% and 64% +/- 5% after 0.1 mmol/kg intravenous administration of gadobenate and gadopentetate, respectively; in MPP+ lesions, the peak signal intensity enhancement was 22% +/- 9%, 32% +/- 7%, and 64% +/- 14% after 0.2 mmol/kg intravenous of gadopentetate, gadobenate, and B-21326/7, respectively. In rabbits, the relaxation enhancement of blood 5 minutes after B-21326/7 and gadobenate administration was 323% and 182%, respectively, relative to the same dose (0.1 mmol/kg intravenous) of gadopentetate.

CONCLUSIONS

Weak protein binding can substantially increase the efficacy of gadolinium chelates as general purpose contrast agents for MRI.

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.

Infarction of the corpus callosum: computed tomography and magnetic resonance imaging

OBJECTIVE

To describe the computed tomography (CT) and magnetic resonance (MR) features of corpus callosum (CC) infarctions.

METHODS

We reviewed retrospectively 352 consecutive cranial CT and MR scans showing cerebral infarcts. Involvement of the CC was identified in 28 patients.

RESULTS

Infarctions of the CC were diffuse (n = 3) or focal (n = 25). The former were seen in the setting of diffuse cerebral ischemia secondary to cardiopulmonary arrest or status epilepticus. The latter were divided into those affecting predominantly the genu, body or splenium. The most common location of the insult was the splenium (n = 13), followed by the body (n = 6) and genu (n = 3). In the remaining three patients combined genu/body infarctions were seen.

CONCLUSION

Infarction of the CC may be more common than previously thought and is most often the result of cerebral embolism. MR is better suited than CT for the detection of vascular lesions of the CC.

Improvement of brain lesion detection at 0.1 T by simultaneous use of Gd-DTPA and magnetization transfer imaging

Imaging parameters were optimized at 0.1 T to improve contrast-to-noise ratios (CNR) when combining magnetization transfer (MT) imaging and the use of paramagnetic contrast medium. This was accomplished by imaging a phantom containing serial concentrations of Gd-DTPA in cross-linked bovine serum albumin. With the use of simulations, the dependence of CNR on imaging parameters was studied. Conventional and MT images were obtained from 10 brain tumor patients with single and triple doses of Gd-DTPA. Simulations demonstrated the importance of TR in postcontrast sequences. The CNR in MT images is less sensitive to TR than in conventional images. A significant CNR improvement caused by MT remains at longer TR when there is no contrast enhancement without MT. The clinical results indicate that a single dose of Gd-DTPA combined with MT cannot replace imaging with a triple dose. However, MT significantly improved the CNR after single and triple Gd-DTPA-doses on T1-weighted and proton-density images.

Application of magnetization transfer imaging for intracranial lesions of tuberous sclerosis

PURPOSE

Our goal was to assess the effectiveness of magnetization transfer imaging (MTI) and the usefulness of the magnetization transfer ratio (MTR) in tuberous sclerosis (TS).

METHOD

T2- and T1-weighted SE images with saturation pulse on/off before and after gadolinium enhancement in 10 patients with TS were obtained. The numbers of subependymal nodule (SEN), cortical tuber, and white matter (WM) abnormality detected on T1-, proton density, T2-, and MT T1-weighted SE images were compared. The contrast-to-noise ratio (C/N) on T1-, MT T1-, Gd T1-, and Gd MT T1-weighted SE images and MTR (1-Msat/MO) on each set of saturation/nonsaturation images for each lesions were calculated. Mean MTRs (mMTRs) of WM and gray matter (GM) from seven normal volunteers were also obtained.

RESULTS

MT T1-weighted SE images always depicted all lesions seen on conventional MRI and allowed depiction of more SENs (n = 80), cortical tubers (n = 197), and WM abnormalities (n = 82) than did T1-weighted (n = 58/85/33), proton density (n = 41/108/36), or T2-weighted (n = 48/121/46) SE images. The best C/N was obtained from Gd MT T1-weighted SE images in SENs and from MT T1-weighted SE images in other lesions. mMTRs of normal WM and GM were 36.43 and 29.42%, respectively. Cortical tubers and WM abnormalities had measured MTRs that were statistically equal to MTRs of GM in normal subjects (p < 0.005). MTRs of SENs showed lower mean (25.55%) and greater diversity (SD +/- 5.30), compared with MTRs of other lesions and normal GM and WM. One SEN with MTR of 20.72% was pathologically confirmed to be subependymal giant cell astrocytoma (SGCA). Nine SENs had measured MTR below 20.72% and six nodules among these were located in the region of the foramen of Monro, which is the characteristic location of SGCA.

CONCLUSION

MTI may be effective in detecting all cranial lesions of TS. MTR may increase the specificity of MRI because it can differentiate the histopathologic subtypes and track and evolution of SEN into SGCA.

Effects of contrast dose, delayed imaging, and magnetization transfer saturation on gadolinium-enhanced MR imaging of brain lesions

This paper discusses the types of paramagnetic agents available for clinical brain imaging and reviews investigations that have sought to optimize the use of these agents by varying the administered dose, delaying the imaging time after contrast administration, and altering image contrast by using magnetization transfer saturation pulses.

Comparison between magnetization transfer contrast and fast spin-echo MR imaging of degenerative disease of the cervical spine at 0.3 T

We compared magnetization transfer contrast (MTC) with gradient recalled echo (GRE) magnetic resonance imaging (MRI) and fast spin-echo (FSE) MRI of the degenerative cervical spine at 0.3 T. Fifty patients with suspected degenerative disease of the cervical spine were prospectively evaluated. Multislice sagittal and axial images of the cervical spine were obtained using MTC GRE sequence [repetition time (TR)/echo time (TE)/flip angle = 750/23/25 degrees] and FSE sequence with peripheral gating (TR/effective TE = 2000-4000/120). Quantitatively, FSE showed higher signal-to-noise ratio and superior disk contrast between normal and degenerative disks, while MTC images showed superior contrast-to-noise ratio for the cerebrospinal fluid (CSF) versus cord and superior CSF homogeneity. In qualitative analysis, similar results were obtained. In conclusion, FSE and MTC GRE sequences are MRI techniques of imaging the cervical spine that have different characteristics and supplement each other in the diagnostic imaging of degenerative disease of the cervical spine.

CT and MRI of stroke

A review of the CT and MRI features of stroke imaging is presented. The pathophysiology of stroke is discussed as a basis for understanding the neuroimaging findings. Neuroimaging is divided according to the time interval between ictus and imaging: hyperacute, acute, subacute, and chronic. Newer MR stroke imaging techniques such as perfusion imaging and diffusion-weighted imaging are presented.

Guidelines for MRI monitoring of the treatment of multiple sclerosis: recommendations of the US Multiple Sclerosis Society's task force

In relapsing-remitting and secondary progressive multiple sclerosis (MS), MRI activity on monthly brain scans is a sensitive primary outcome measure in short term exploratory treatment trials. Because conventional MRI findings have a limited correlation with disability, the primary outcome in definitive trials should be clinical, although MRI is useful in providing an index of pathological progression. In trials aimed at preventing evolution from a clinically isolated syndrome to MS, MRI findings should be used in the entry criteria. The likely pathological substrates of irreversible disability are demyelination and axonal loss. Putative MR markers for these pathologies appear to relate more closely to disability than conventional MRI findings. Further technical developments should lead to improved quantitation, pathological specificity and clinical correlations.

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 (T1w) did not differ between tumor groups, whereas the T1s, the apparent MT relaxation times (T1a), and the parameters MT contrast (MTC) differed significantly between several tumor types. The MT rates (Rwm) demonstrated the most significant differences; Rwm values could reliably separate high grade and low grade gliomas. T1ws 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.

Experimental acute cerebral ischemia with reperfusion. Evaluation with gadolinium-texaphyrin

RATIONALE AND OBJECTIVES

The authors explore the potential usefulness of the new contrast medium gadolinium (Gd)-texaphyrin (PCI-0101) in magnetic resonance imaging of experimental acute cerebral ischemia with reperfusion.

METHODS

Four New Zealand white rabbits underwent 2 hours of transorbital occlusion of the left internal carotid, anterior, and middle cerebral arteries, followed by 2 hours of reperfusion with normal saline. Immediately thereafter, the rabbits were injected with 25 mumol/kg of 2 mmol/L Gd-texaphyrin and killed by barbiturate overdose. Postmortem T1- and T2-weighted coronal scans were performed at 1.5 Tesla and correlated with histopathologic findings.

RESULTS

Postcontrast T1-weighted images showed high signal within extensive cortical and basal ganglia infarcts. Areas of high signal on T1-weighted images were less extensive than on T2-weighted images, and corresponded to only a portion of the region of neuronal damage seen histologically. Signal intensity of infarcted brain on postcontrast T1-weighted images was significantly greater than normal brain in the contralateral hemisphere (P < 0.0014).

CONCLUSIONS

Experimental reperfused infarcts only 2 hours old demonstrate contrast enhancement with Gd-texaphyrin.

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 T1-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 < .01]; hemangioma 24 +/- 2.1 [P < .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.