Dynamic contrast-enhanced T2*-weighted MR imaging of tumefactive demyelinating lesions.

PURPOSE: Dynamic contrast-enhanced T2*-weighted MR imaging has been helpful in characterizing intracranial mass lesions by providing information on vascularity. Tumefactive demyelinating lesions (TDLs) can mimic intracranial neoplasms on conventional MR images, can be difficult to diagnose, and often result in surgical biopsy for suspected tumor. The purpose of this study was to determine whether dynamic contrast-enhanced T2*-weighted MR imaging can be used to distinguish between TDLs and intracranial neoplasms that share common features on conventional MR images. METHODS: We retrospectively reviewed the conventional and dynamic contrast-enhanced T2*-weighted MR images and medical records of 10 patients with tumefactive demyelinating disease that was diagnosed by either biopsy or strong clinical suspicion supported by laboratory evaluation that included CSF analysis and evoked potential tests. Twelve TDLs in 10 patients and 11 brain tumors that appeared similar on conventional MR images were studied. Relative cerebral blood volume (rCBV) was calculated from dynamic MR data and was expressed as a ratio to contralateral normal white matter. rCBV values from 11 patients with intracranial neoplasms with very similar conventional MR imaging features were used for comparison. RESULTS: The rCBV values of TDLs ranged from 0.22 to 1.79 (n = 12), with a mean of 0.88 +/- 0.46 (SD). The rCBV values of intracranial neoplasms ranged from 1.55 to 19.20 (n = 11), with a mean of 6.47 +/- 6.52. The difference in rCBV values between the two groups was statistically significant (P =.009). The difference in rCBV values between TDLs and primary cerebral lymphomas (n = 4) was less pronounced but was statistically significant (P =.005). CONCLUSION: Dynamic contrast-enhanced T2*-weighted MR imaging is a useful diagnostic tool in differentiating TDLs from intracranial neoplasms and may therefore obviate unnecessary surgical biopsy.     

Perfusion magnetic resonance imaging in intracerebral parenchymal tuberculosis: preliminary findings

OBJECTIVES: To study the vascular perfusion patterns of focal intracerebral tubercular lesions using echoplanar magnetic resonance (MR) imaging-derived relative cerebral blood volume (rCBV) maps. METHODS: Seventeen focal tubercular lesions were evaluated with conventional and perfusion-weighted MR imaging on a 1.5-T MR system. The rCBVs of the center, peripheral wall, and perilesional white matter were calculated from the perfusion MR-derived data. Perfusion MR imaging findings as depicted on the rCBV maps were qualitatively compared with those of conventional MR findings. RESULTS: Eleven of the 17 lesions demonstrated vascularity greater than that of the contralateral white matter on rCBV maps. The mean of the measured rCBV values of the peripheral wall and center of the lesions was 2.5 +/- 1.42 and 0.33 +/- 0.3 (mean +/- SD), respectively. Most of the hypervascular lesions (8) revealed a concentric peripheral wall having alternating hypointense and hyperintense signal intensity rims surrounding a variable intensity center on T2-weighted images. All the lesions having a nodular enhancing pattern (4) were hypervascular. CONCLUSIONS: Focal cerebral tubercular lesions can have variable vascularity as shown on perfusion MR-derived rCBV maps. It may be difficult to differentiate hypervascular lesions from cerebral tumors in some patients based on perfusion MR imaging alone.     

Dynamic contrast-enhanced T2*-weighted MR imaging of gliomatosis cerebri

BACKGROUND AND PURPOSE: MR imaging characteristics of gliomatosis cerebri reiterate the diffuse nature of this tumor but are nonspecific and thus may pose a diagnostic challenge. Because perfusion MR imaging can provide a physiologic map of the microcirculation, we compared the measured relative cerebral blood volume (rCBV) at perfusion imaging with histopathologic findings in gliomatosis cerebri. MR spectroscopic findings were also reviewed. METHODS: Retrospective analysis was performed of conventional and perfusion MR images from seven patients with proved gliomatosis cerebri. The conventional MR images were evaluated for the presence or absence of contrast enhancement, necrosis, and extent of T2-weighted signal intensity abnormality. Dynamic contrast-enhanced T2*-weighted gradient-echo echo-planar images were acquired during the first pass of a bolus injection of gadopentetate dimeglumine. The rCBV was calculated by using nondiffusible tracer kinetics and expressed relative to normal-appearing white matter. Pathologic findings were reviewed in all patients and compared with the MR perfusion data. Multivoxel 2D chemical shift imaging proton MR spectroscopic data were available for three patients and single-voxel data for one patient. RESULTS: Conventional MR images showed diffuse abnormality in all cases and absence of contrast enhancement in all but one case. Average rCBV range was 0.75-1.26 (mean, 1.02 +/- 0.42 [SD]). MR spectroscopic data revealed spectra consistent with presence of tumoral disease. Histopathologic review showed absence of vascular hyperplasia in all specimens. CONCLUSION: The low MR rCBV measurements of gliomatosis cerebri are in concordance with the lack of vascular hyperplasia found at histopathologic examination; thus, perfusion MR imaging provides useful adjunctive information that is not available from conventional MR imaging techniques.     

MR digital subtraction angiography in the diagnosis of meningiomas

OBJECTIVE: MR digital subtraction angiography (DSA) is a technique for demonstrating the vasculature combining a rapid two-dimensional T1-weighted sequence with a bolus injection of gadolinium. We attempted to determine its contribution to the diagnosis of intracranial meningiomas. METHODS AND PATIENTS: MR DSA was performed in 18 patients with meningioma as well as in 28 patients with other tumors. The findings were analyzed regarding demonstration of tumor stain and tumor-related vessels. RESULTS: All meningiomas except one were visualized as a homogeneous and intense stain. Feeding arteries were visualized in 2 patients, and draining or abnormal veins in three. In 21 of the 28 patients with other tumors, tumor stains of varying degrees were demonstrated. CONCLUSION: MR DSA can serve as an adjunct to routine MR imaging, because it enables assessment of the hemodynamics of meningiomas and facilitates its differential diagnosis from other tumors.     

Cerebral hemodynamics on MR perfusion images before and after bypass surgery in patients with giant intracranial aneurysms.

BACKGROUND AND PURPOSE: Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm.     

Dynamic susceptibility contrast MR imaging: correlation of signal intensity changes with cerebral blood volume measurements

Cerebral blood volume (CBV) maps derived from dynamic susceptibility contrast (DSC) magnetic resonance (MR) imaging provide valuable information regarding intracranial micro-hemodynamics and have been helpful in characterizing primary brain tumors and guiding stereotactic biopsy. Another parameter, the maximum signal drop (MSD) during the first pass of intravascular contrast bolus due to T2* effect, can also be measured directly without extensive post-processing and data manipulation. The purpose of our study is to determine whether MSD maps provide information similar to CBV maps in patients presenting with intracranial mass lesions. Twenty-nine patients with various intracranial mass lesions were studied with DSC MR imaging prior to stereotactic biopsy or volumetric resection. Maps of both CBV and MSD are calculated on a pixel-by-pixel basis and displayed as color overlays over the raw images. Relative CBV (rCBV) and MSD (rMSD) values were measured in regions of interest (ROIs) within areas of abnormality and compared. In addition, computer-generated noise was added to the data to estimate the sensitivity of each measurement to noise. The rMSD values were strongly correlated with rCBV values (r = 0.87, P = 0.0001). CBV values were much more sensitive to added noise than MSD values (P < 0.01). MSD maps derived from DSC MR imaging provide information similar to CBV maps in patients with intracranial mass lesions. MSD maps are a simple and reliable indicator of vascularity that can easily be incorporated into routine MR imaging.     

Pulmonary arterial hypertension: diagnosis with fast perfusion MR imaging and high-spatial-resolution MR angiography--preliminary experience

PURPOSE: To determine prospectively the accuracy of a magnetic resonance (MR) perfusion imaging and MR angiography protocol for differentiation of chronic thromboembolic pulmonary arterial hypertension (CTEPH) and primary pulmonary hypertension (PPH) by using parallel acquisition techniques. MATERIALS AND METHODS: The study was approved by the institution's internal review board, and all patients gave written consent prior to participation. A total of 29 patients (16 women; mean age, 54 years +/- 17 [+/- standard deviation]; 13 men; mean age, 57 years +/- 15) with known pulmonary hypertension were examined with a 1.5-T MR imager. MR perfusion imaging (temporal resolution, 1.1 seconds per phase) and MR angiography (matrix, 512; voxel size, 1.0 x 0.7 x 1.6 mm) were performed with parallel acquisition techniques. Dynamic perfusion images and reformatted three-dimensional MR angiograms were analyzed for occlusive and nonocclusive changes of the pulmonary arteries, including perfusion defects, caliber irregularities, and intravascular thrombi. MR perfusion imaging results were compared with those of radionuclide perfusion scintigraphy, and MR angiography results were compared with those of digital subtraction angiography (DSA) and/or contrast material-enhanced multi-detector row computed tomography (CT). Sensitivity, specificity, and diagnostic accuracy of MR perfusion imaging and MR angiography were calculated. Receiver operator characteristic analyses were performed to compare the diagnostic value of MR angiography, MR perfusion imaging, and both modalities combined. For MR angiography and MR perfusion imaging, kappa values were used to assess interobserver agreement. RESULTS: A correct diagnosis was made in 26 (90%) of 29 patients by using this comprehensive MR imaging protocol. Results of MR perfusion imaging demonstrated 79% agreement (ie, identical diagnosis on a per-patient basis) with those of perfusion scintigraphy, and results of MR angiography demonstrated 86% agreement with those of DSA and/or CT angiography. Interobserver agreement was good for both MR perfusion imaging and MR angiography (kappa = 0.63 and 0.70, respectively). CONCLUSION: The combination of fast MR perfusion imaging and high-spatial-resolution MR angiography with parallel acquisition techniques enables the differentiation of PPH from CTEPH with high accuracy.     

Correlation between dynamic susceptibility contrast perfusion MRI and methionine metabolism in brain gliomas: preliminary results

PURPOSE: To evaluate in brain gliomas the relationship between tumor vascularity measured by MR-based maximum regional cerebral blood volume (rCBV) and tumor amino-acid metabolism based on maximum carbon-11 methionine (MET) uptake on positron emission tomography (PET). MATERIALS AND METHODS: Eighteen patients with histologically proven primary brain gliomas were included in the study. In addition to conventional MR sequences, dynamic MR images, including a first-pass gadopentetate dimeglumine T2*-weighted echo-planar perfusion sequence and a PET study using MET, were acquired. Eleven patients had low-grade gliomas, and seven had high-grade gliomas. rCBV ratios and MET uptake ratios normalized to the contralateral white matter (WM) corresponding values were measured in each tumor. Both maximum rCBV ratios and maximum MET uptake ratios were correlated to histopathology. The maximum rCBV ratios were correlated to the maximum MET uptake ratios. RESULTS: Both the maximum rCBV ratios and maximum MET uptake ratios of high-grade gliomas were significantly higher than those of low-grade gliomas (P<0.05). There was a significant positive correlation between maximum rCBV ratios and maximum MET uptake ratios (Spearman: r=0.89, P<0.00001). CONCLUSION: The maximum rCBV ratio and maximum MET uptake ratio are significantly correlated in gliomas, reflecting a close link between amino acid uptake and vascularity in these tumors.     

VIBE MRI for evaluating the normal and abnormal gastrointestinal tract in fetuses

OBJECTIVE: The great potential of MRI for assessing gastrointestinal abnormalities in fetuses has been described. T1-weighted images may add additional information to T2-weighted images in diagnosing fetal gastrointestinal abnormalities. The objective of this study was to assess the performance of a 3D volumetric interpolated breath-hold sequence (VIBE) in evaluating the normal and abnormal fetal gastrointestinal tract. CONCLUSION: VIBE provides high-quality T1-weighted and 3D MR colonography images for the evaluation of the normal and abnormal gastrointestinal tract in fetuses, and 3D MR colonography provides excellent delineation of the meconium.     

MR动态减影血管造影在脑动静脉畸形治疗前后中的评价

目的评价MR动态减影血管造影（MR-DSA）在脑动静脉畸形（AVM）栓塞治疗前后的价值和限度。方法22例AVM患者，在栓塞前后均行MR—DSA、三维增强MR血管造影（3D—CEMRA）、MR质子加权成像（PWI）和DSA检查，同时由2名有经验的医生独立进行双盲对照研究。结果MR-DSA和DSA在22例AVM栓塞前后的瘤巢大小及分类上结果一致，MR—DSA能够显示AVM栓塞后的血液动力学改变，瘤巢及引流静脉显影推迟17例，瘤巢变小13例（其中完全消失4例），与DSA符合率为100％。与DSA相比，MR-DSA没有显示瘤巢内动脉瘤和栓塞后引流静脉及供血动脉直径变小各1例，而3D-CEMRA对此显示清晰。栓塞后的PWI与栓塞前相比，22例均可见不同程度的高信号。结论MR—DSA是1种快速、有效、无创的血管造影检查方法，能提供AVM栓塞前后的血流动力学信息，MR—DSA、3D-CEMRA和PWI应在AVM的随访中相互结合，综合运用。     

Prospective evaluation of suspected stenoocclusive disease of the intracranial artery: combined MR angiography and CT angiography compared with digital subtraction angiography

BACKGROUND AND PURPOSE: MR angiography is primarily and increasingly used to assess intracranial arterial stenoocclusion. However, MR angiography can cause overestimation of stenosis. Although CT angiography is accurate, it has limitations. Our purpose was to determine whether the accuracy of combined MR angiography and CT angiography is equal to that of digital subtraction angiography (DSA) in measuring stenosis and detecting major intracranial arterial occlusion. METHODS: CT angiography and intraarterial DSA were prospectively performed in 18 patients with suspected intracranial stenoocclusive disease, as revealed with MR angiography. Before DSA, two reviewers independently assessed MR intracranial angiograms. Subsequently, they assessed CT angiograms with MR angiograms. Results were compared with DSA results. The degree of stenoocclusion was categorized; stenosis of 50% or more indicated stenoocclusive disease. After the blinded study, two radiologists retrospectively reviewed the angiographic findings. RESULTS: Stenoocclusive disease was identified in 18 of 198 intracranial arteries at DSA. MR angiography had a sensitivity of 92%, a specificity of 91%, and an accuracy of 91% for the identification of stenosis of 50% or more; the addition of CT angiography yielded values of 100%, 99%, and 99%, respectively. Stenotic grades with combined CT angiography and MR angiography agreed with those of DSA in 98% of cases. In the retrospective study, CT angiography did not always correctly delineate arterial lumina with circumferential calcification and cavernous portions of the internal carotid artery. CONCLUSION: In this investigation, the evaluation of suspected stenoocclusive diseases in major intracranial arteries, the accuracy of combined MR angiography and CT angiography is equal to that of DSA in most cases.     

Clinical relevance of diffusion and perfusion magnetic resonance imaging in assessing intra-axial brain tumors

Advanced magnetic resonance (MR) imaging techniques provide physiologic information that complements the anatomic information available from conventional MR imaging. We evaluated the roles of diffusion and perfusion imaging for the assessment of grade and type of histologically proven intraaxial brain tumors. A total of 28 patients with intraaxial brain tumors underwent conventional MR imaging (T2- and T1-weighted sequences after gadobenate dimeglumine injection), diffusion imaging and T2*-weighted echo-planar perfusion imaging. Examinations were performed on 19 patients during initial diagnosis and on nine patients during follow-up therapy. Determinations of relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) were performed in the solid parts of each tumor, peritumoral region and contralateral white matter. For gliomas, rCBV values were greater in high-grade than in low-grade tumors (3.87±1.94 versus 1.30±0.42) at the time of initial diagnosis. rCBV values were increased in all recurrent tumors, except in one patient who presented with a combination of recurrent glioblastoma and massive radionecrosis on histology. Low-grade gliomas had low rCBV even in the presence of contrast medium enhancement. Differentiation between high- and low-grade gliomas was not possible using diffusion-weighted images and ADC values alone. In the peritumoral areas of untreated high-grade gliomas and metastases, the mean rCBV values were higher for high-grade gliomas (1.7±0.37) than for metastases (0.54±0.18) while the mean ADC values were higher for metastases. The rCBV values of four lymphomas were low and the signal intensity–time curves revealed a significant increase in signal intensity after the first pass of gadobenate dimeglumine. Diffusion and perfusion imaging, even with relatively short imaging and data processing times, provide important information for lesion characterization.     

Preliminary experience with dynamic MR projection angiography in the evaluation of cervicocranial steno-occlusive disease

The application of a contrast-enhanced, two-dimensional MR technique, which provides dynamic projection angiograms at a subsecond temporal frame rate for depiction of the cervical and intracranial arteries, was evaluated in three healthy volunteers and seven patients with various cervicocranial steno-occlusive diseases. Intra-arterial digital subtraction angiography (DSA) served as standard of reference for findings in the patients. Magnetic resonance projection angiography (MRPA) was performed on a standard 1.5-T clinical MR imaging system at intravenous injection of a single dose of contrast agent (0.1 mmol/kg GdDTPA-BMA). Sixty consecutive images of the cerebral circulation were acquired at a temporal frame rate of 900 ms per image in the coronal plane. The collateral flow and the perfusion of the compromised vessel territory were readily assessed by MPRA in patients with occlusion of the internal cerebral artery (ICA) or middle cerebral artery (MCA). The leptomeningeal collateralisation of these patients was displayed in a dynamic fashion. Furthermore, quantitative perfusion measurement provided a difference between both MCA territories in the time to peak (ΔDTTP) of the contrast bolus of 1.12 ± 0.28 s in five patients with severe stenosis or occlusion of the ICA (healthy volunteers 0.19 ± 0.05 s). However, important pathological findings, such as the evaluation of carotid artery stenoses and the intracranial collateral flow pattern in patients with severe carotid stenoses, were not sufficiently assessable as compared with DSA. We conclude that the possibility of obtaining simultaneously information about morphology and perfusion dynamics of the cervicocranial vessels is unique in MPRA as compared with other MR techniques. However, in the applied form, the technique is not a reliable tool for the complete evaluation of the cervicocranial vessels in patients with steno-occlusive disease. Received: 27 January 2000/Revised: 11 July 2000/Accepted: 13 July 2000     

Perfusion MR imaging for differentiation of benign and malignant meningiomas

INTRODUCTION: Our purpose was to determine whether perfusion MR imaging can be used to differentiate benign and malignant meningiomas on the basis of the differences in perfusion of tumor parenchyma and/or peritumoral edema. METHODS: A total of 33 patients with preoperative meningiomas (25 benign and 8 malignant) underwent conventional and dynamic susceptibility contrast perfusion MR imaging. Maximal relative cerebral blood volume (rCBV) and the corresponding relative mean time to enhance (rMTE) (relative to the contralateral normal white matter) in both tumor parenchyma and peritumoral edema were measured. The independent samples t-test was used to determine whether there was a statistically significant difference in the mean rCBV and rMTE ratios between benign and malignant meningiomas. RESULTS: The mean maximal rCBV values of benign and malignant meningiomas were 7.16+/-4.08 (mean+/-SD) and 5.89+/-3.86, respectively, in the parenchyma, and 1.05+/-0.96 and 3.82+/-1.39, respectively, in the peritumoral edema. The mean rMTE values were 1.16+/-0.24 and 1.30+/-0.32, respectively, in the parenchyma, and 0.91+/-0.25 and 1.24+/-0.35, respectively, in the peritumoral edema. The differences in rCBV and rMTE values between benign and malignant meningiomas were not statistically significant (P>0.05) in the parenchyma, but both were statistically significant (P<0.05) in the peritumoral edema. CONCLUSION: Perfusion MR imaging can provide useful information on meningioma vascularity which is not available from conventional MRI. Measurement of maximal rCBV and corresponding rMTE values in the peritumoral edema is useful in the preoperative differentiation between benign and malignant meningiomas.     

Differentiation of cerebral tumors using multi-section echo planar MR perfusion imaging

OBJECTIVE: We have investigated the performance of magnetic resonance (MR) perfusion imaging to differentiate between astrocytomas grade II, grade III and glioblastomas in a prospective study. MATERIALS AND METHODS: In 33 patients with suspected supratentorial primary cerebral tumors we performed multi-section Echo Planar MR perfusion imaging. Regional cerebral blood volume (rCBV) maps were calculated and the maximum rCBV was determined from the entire lesion. This value was divided by the mean rCBV value from the contralateral side, which provided the rCBV index used in this study. The rCBV index was correlated with the histological tumor classification after stereotactic biopsy (n=7) or open resection (n=26). RESULTS: The maximum rCBV index was 1.2+/-0.8 for grade II astrocytomas (n=3), 4.0+/-1.2 for grade III astrocytomas (n=13), and 10.3+/-3.3 for glioblastomas (n=17). The difference between grade III astrocytomas and glioblastomas was highly significant (P<0.001). DISCUSSION AND CONCLUSION: The rCBV index measured with multi-section Echo Planar MR perfusion is capable of differentiating grade III astrocytomas from glioblastomas. It serves as an additional parameter to establish a diagnosis in cases where it is not possible to clearly differentiate between these types of tumors on the basis of conventional MR imaging. MR perfusion imaging also provides information about spatial heterogeneities within a tumor which might improve diagnostic performance. This technology may also be of interest for follow-up examinations after histological diagnosis and further treatment.     

Evaluation of therapeutic effectiveness of transarterial chemoembolization for hepatocellular carcinoma: correlation of dynamic susceptibility contrast-enhanced echoplanar imaging and hepatic angiography

The objective of this study was to evaluate the therapeutic effectiveness of transarterial chemoembolization (TACE) for hepatocellular carcinoma (HCC) with dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI). Seventeen patients with histopathologically proven HCC were included in this study. All patients underwent MR examinations with conventional T1- and T2-weighted images, gadolinium-enhanced images, and DSC-MRI before TACE treatment. Hepatic blood volume (HBV) maps were reconstructed from the time-intensity curves. The same MRI sequences and techniques were repeated 24 h and 6 weeks after TACE. Serial changes in tumor perfusion on HBV maps were correlated with vascularity in hepatic angiography. All tumors were hypointense on T1-weighted images and hyperintense on T2-weighted images. Heterogeneous enhancement was observed in all tumors before and immediately after TACE. Hyperperfusion was noted in most of the tumors on HBV map before TACE and moderate to marked hypoperfusion following TACE. The degree of tumor perfusion on HBV map correlated well with the vascularity in angiography. In conclusion, the noninvasive nature of DSC-MRI is useful to evaluate the effectiveness of TACE. Invasive procedures, such as angiography, are seldom necessary.     

Relative cerebral blood volume maps corrected for contrast agent extravasation significantly correlate with glioma tumor grade, whereas uncorrected maps do not

BACKGROUND AND PURPOSE: Relative cerebral blood volume (rCBV) estimates for high-grade gliomas computed with dynamic susceptibility contrast MR imaging are artificially lowered by contrast extravasation through a disrupted blood-brain barrier. We hypothesized that rCBV corrected for agent leakage would correlate significantly with histopathologic tumor grade, whereas uncorrected rCBV would not. METHODS: We performed dynamic T2*-weighted perfusion MR imaging on 43 patients with a cerebral glioma after prebolus gadolinium diethylene triamine penta-acetic acid administration to diminish competing extravasation-induced T1 effects. The rCBV was computed from non-necrotic enhancing tumor regions by integrating the relaxivity-time data, with and without contrast extravasation correction by using a linear fitting algorithm, and was normalized to contralateral brain. We determined the statistical correlation between corrected and uncorrected normalized rCBV and histopathologic tumor grade with the Spearman rank correlation test. RESULTS: Eleven, 9, and 23 patients had WHO grades II, III, and IV glioma, respectively. Mean uncorrected normalized rCBVs were 1.53, 2.51, and 2.14 (grade II, III, and IV). Corrected normalized rCBVs were 1.52, 2.84, and 3.96. Mean absolute discrepancies between uncorrected and corrected rCBVs were 2% (0%-15%), 16% (0%-106%), and 74% (0%-411%). The correlation between corrected rCBV and tumor grade was significant (0.60; P < .0001), whereas it was not for uncorrected rCBV (0.15; P = .35). CONCLUSION: For gliomas, rCBV estimation that correlates significantly with WHO tumor grade necessitates contrast extravasation correction. Without correction, artificially lowered rCBV may be construed erroneously to reflect lower tumor grade.     

Diffusion-perfusion in intra-axial brain tumors with high relaxivity contrast agents

A high relaxivity contrast agent is indicated for use in MRI of the central nervous system to visualize lesions with an abnormal blood-brain barrier (BBB) or abnormal vascularity of the brain. We evaluated MultiHance (gadobenate dimeglumine, Gd-BOPTA) on T2*-weighted perfusion imaging in 33 histologically proven intra-axial brain tumors. The higher T1 relaxivity, and therefore better contrast-enhanced T1 imaging led to significantly better tumor delineation. The higher T2 relaxivity allowed high quality T2* perfusion MRI and post processed rCBV maps, with a dose of 0.1 mmol/kg MultiHance.     

Perfusion-sensitive MRI of pilocytic astrocytomas: initial results

Purpose To present the imaging and perfusion data obtained in nine patients with pilocytic astrocytomas (PA) and to discuss the original functional issues of this technique. Method Nine patients with pathologically proven PA underwent conventional and perfusion MR imaging. Various areas of relative cerebral blood volume (rCBV) within the tumors were obtained. The maximum rCBV ratios were identified and considered as representative of the tumor. The results were compared with the pathological findings. Results In all patients, rCBV was <1.5 (mean 1) and the signal intensity curve overshot the baseline. Conclusion PA tend to have low rCBV values and a first-pass curve that crosses the baseline. These characteristics may be explained by the histological profile of the tumoral vascularity and are of relevance in the identification of these rare tumors.     

Glioma grading: sensitivity, specificity, and predictive values of perfusion MR imaging and proton MR spectroscopic imaging compared with conventional MR imaging

BACKGROUND AND PURPOSE: Sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of conventional MR imaging in predicting glioma grade are not high. Relative cerebral blood volume (rCBV) measurements derived from perfusion MR imaging and metabolite ratios from proton MR spectroscopy are useful in predicting glioma grade. We evaluated the sensitivity, specificity, PPV, and NPV of perfusion MR imaging and MR spectroscopy compared with conventional MR imaging in grading primary gliomas. METHODS: One hundred sixty patients with a primary cerebral glioma underwent conventional MR imaging, dynamic contrast-enhanced T2*-weighted perfusion MR imaging, and proton MR spectroscopy. Gliomas were graded as low or high based on conventional MR imaging findings. The rCBV measurements were obtained from regions of maximum perfusion. Metabolite ratios (choline [Cho]/creatine [Cr], Cho/N-acetylaspartate [NAA], and NAA/Cr) were measured at a TE of 144 ms. Tumor grade determined with the three methods was then compared with that from histopathologic grading. Logistic regression and receiver operating characteristic analyses were performed to determine optimum thresholds for tumor grading. Sensitivity, specificity, PPV, and NPV for identifying high-grade gliomas were also calculated. RESULTS: Sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 72.5%, 65.0%, 86.1%, and 44.1%, respectively. Statistical analysis demonstrated a threshold value of 1.75 for rCBV to provide sensitivity, specificity, PPV, and NPV of 95.0%, 57.5%, 87.0%, and 79.3%, respectively. Threshold values of 1.08 and 1.56 for Cho/Cr and 0.75 and 1.60 for Cho/NAA provided the minimum C2 and C1 errors, respectively, for determining a high-grade glioma. The combination of rCBV, Cho/Cr, and Cho/NAA resulted in sensitivity, specificity, PPV, and NPV of 93.3%, 60.0%, 87.5%, and 75.0%, respectively. Significant differences were noted in the rCBV and Cho/Cr, Cho/NAA, and NAA/Cr ratios between low- and high-grade gliomas (P <.0001,.0121,.001, and.0038, respectively). CONCLUSION: The rCBV measurements and metabolite ratios both individually and in combination can increase the sensitivity and PPV when compared with conventional MR imaging alone in determining glioma grade. The rCBV measurements had the most superior diagnostic performance (either with or without metabolite ratios) in predicting glioma grade. Threshold values can be used in a clinical setting to evaluate tumors preoperatively for histologic grade and provide a means for guiding treatment and predicting postoperative patient outcome.