Diagnostic Accuracy of Neuroimaging to Delineate Diffuse Gliomas within the Brain: A Meta-Analysis

BACKGROUND:Brain imaging in diffuse glioma is used for diagnosis, treatment planning, and follow-up.PURPOSE:In this meta-analysis, we address the diagnostic accuracy of imaging to delineate diffuse glioma.DATA SOURCES:We systematically searched studies of adults with diffuse gliomas and correlation of imaging with histopathology.STUDY SELECTION:Study inclusion was based on quality criteria. Individual patient data were used, if available.DATA ANALYSIS:A hierarchic summary receiver operating characteristic method was applied. Low- and high-grade gliomas were analyzed in subgroups.DATA SYNTHESIS:Sixty-one studies described 3532 samples in 1309 patients. The mean Standard for Reporting of Diagnostic Accuracy score (13/25) indicated suboptimal reporting quality. For diffuse gliomas as a whole, the diagnostic accuracy was best with T2-weighted imaging, measured as area under the curve, false-positive rate, true-positive rate, and diagnostic odds ratio of 95.6%, 3.3%, 82%, and 152. For low-grade gliomas, the diagnostic accuracy of T2-weighted imaging as a reference was 89.0%, 0.4%, 44.7%, and 205; and for high-grade gliomas, with T1-weighted gadolinium-enhanced MR imaging as a reference, it was 80.7%, 16.8%, 73.3%, and 14.8. In high-grade gliomas, MR spectroscopy (85.7%, 35.0%, 85.7%, and 12.4) and ¹¹C methionine–PET (85.1%, 38.7%, 93.7%, and 26.6) performed better than the reference imaging.LIMITATIONS:True-negative samples were underrepresented in these data, so false-positive rates are probably less reliable than true-positive rates. Multimodality imaging data were unavailable.CONCLUSIONS:The diagnostic accuracy of commonly used imaging is better for delineation of low-grade gliomas than high-grade gliomas on the basis of limited evidence. Improvement is indicated from advanced techniques, such as MR spectroscopy and PET.

Diffuse gliomas are the most common primary brain tumors in adults, with an annual incidence of approximately 6 per 100,000. Despite advances in neurosurgery, radiation therapy, and chemotherapy, gliomas are fatal.¹ Brain imaging is indispensable for diagnosis, treatment planning, evaluation, and follow-up. Although imaging standards to plan resection and radiation therapy vary between institutions and specialists, conventional imaging is in common use, typically consisting of T1-weighted MR imaging before and after gadolinium and T2/FLAIR-weighted imaging for gliomas. Of these conventional sequences, T2/FLAIR-weighted imaging is often considered as a reference for low-grade gliomas, and T1-weighted gadolinium-enhanced imaging, for high-grade gliomas in neurosurgical planning, combined with T2-weighted imaging in radiation therapy planning.^2,3Compared with other cancer types, accurate delineation of gliomas within the brain for treatment planning is particularly important due to the proximity of eloquent brain structures, which are vulnerable to surgery and radiation therapy.⁴ Conversely, more extensive resections and boosted radiation therapy correlate with longer survival.^5–7 At the same time, clinical observations challenge the diagnostic accuracy of current imaging protocols: Gliomas recur even after a radiologically complete resection,^8,9 and glioma cells have been detected outside MR imaging abnormalities.^10,11 Brain imaging techniques, such as multivoxel spectroscopy and PET, were developed to improve tumor grading and delineation.^12,13Inherent in any regional treatment, such as surgery and radiation therapy, is the need to delineate a target volume, which mandates a dichotomous classification into tumor and normal tissue. Low- and high-grade gliomas have different treatment strategies and prognosis, while both are characterized by diffuse tumor infiltration. This supports our pooled analysis for diffuse glioma in addition to subgroup analysis by glioma grade. More accurate glioma delineation may improve the consistency between treatment results and survival. For instance, more accurate delineation may serve to identify patients eligible for more aggressive surgery than would have been considered on the basis of conventional imaging and may identify patients with glioma infiltration beyond meaningful surgical therapy so that useless and possibly harmful resections can be avoided.The diagnostic accuracy of imaging techniques to delineate gliomas has not been systematically addressed, to our knowledge. In this meta-analysis, we estimate and compare the diagnostic accuracies of conventional imaging techniques and advanced MR imaging and PET to delineate newly diagnosed diffuse gliomas within brain tissue in adults.     

Dynamic contrast-enhanced T2-weighted MR imaging of recurrent malignant gliomas treated with thalidomide and carboplatin

BACKGROUND AND PURPOSE: Dynamic, contrast-enhanced MR imaging has allowed quantitative assessment of cerebral blood volume (CBV) in brain tumors. The purpose of our study was to compare postcontrast T1-weighted imaging with dynamic, contrast-enhanced T2*-weighted echo-planar imaging in the evaluation of the response of recurrent malignant gliomas to thalidomide and carboplatin. METHODS: Serial MR imaging was performed in 18 consecutive patients with recurrent malignant gliomas receiving both thalidomide and carboplatin for 12-month periods. Six patients undergoing carboplatin therapy alone were chosen as control subjects. Conventional postcontrast T1-weighted images were compared with relative CBV (rCBV) maps calculated on a pixel-by-pixel basis from dynamic echo-planar imaging data. Tumor progression was evaluated clinically using established criteria for malignant gliomas. Studies were performed at 2- to 3-month intervals, and imaging and clinical findings were compared. RESULTS: Tumor response to treatment, based on clinical findings, did not correlate well with conventional imaging findings. The rCBV values decreased significantly in all patients between the start of therapy and the first follow-up in the study group, but not in the control group. The difference in rCBV values between the clinically stable and the progressive group at 12-month follow-up was statistically significant, with the progressive group having higher values. CONCLUSION: Dynamic, contrast-enhanced MR imaging is a valuable adjunct to conventional imaging in assessing tumor activity during antiangiogenic therapy, and correlates better than conventional studies with clinical status and response to therapy.     

Preliminary experience with MR-guided thermal ablation of brain tumors.

PURPOSETo evaluate the feasibility of a technique of MR-guided stereotactic radio frequency ablation, which was developed as a minimally invasive treatment for brain tumors, and to determine MR characteristics and sequential evolution of radio frequency lesions created to ablate brain tumors.METHODSFourteen lesions in 12 patients with primary and metastatic brain tumors were treated with this technique and followed for up to 10 months. The stereotactic coordinates of the tumor and the angle of the radio frequency probe were calculated on MR imaging. The radio frequency lesion was generated in the awake patient by increasing the temperature to 80 degrees C within the tumor for 1 minute. This was repeated until the entire tumor volume was destroyed. MR imaging was performed before, during, and immediately after the radio frequency procedure, and sequential MR was obtained during clinical follow-up.RESULTSMR imaging clearly showed well-defined radio frequency lesions and provided feedback for treatment planning. The radio frequency lesion boundary was well identified as a dark signal rim on T2-weighted images and showed ring enhancement on contrast-enhanced T1-weighted images. The sequential MR imaging showed the radio frequency lesions decreased in volume in all cases, suggesting focal control.CONCLUSIONStereotactic MR-guided radio frequency brain tumor ablation is a feasible and promising technique that can be an attractive brain tumor treatment alternative. MR provided not only accurate tumor location but also visualization of feedback of thermal tissue changes that reflected therapeutic effect.     

Evaluation of treatment response of chemoembolization in hepatocellular carcinoma with diffusion-weighted imaging on 3.0-T MR imaging

PurposeTo assess the treatment response of hepatocellular carcinoma (HCC) after transarterial chemoembolization with diffusion-weighted imaging and dynamic contrast-enhanced magnetic resonance (MR) imaging with a 3-T system.Materials and MethodsBetween February 2010 and November 2010, 74 patients were treated with chemoembolization in our interventional radiology unit. Twenty-two patients (29%) who had liver MR imaging including diffusion and dynamic contrast-enhanced MR imaging on a 3-T system before and after transarterial chemoembolization were evaluated retrospectively. Tumor size, arterial enhancement, venous washout, and apparent diffusion coefficient (ADC) values of lesions, peritumoral parenchyma, normal liver parenchyma, and spleen were recorded before and after treatment. The significance of differences between ADC values of responding and nonresponding lesions was calculated.ResultsThe study included 77 HCC lesions (mean diameter, 31.4 mm) in 20 patients. There was no significant reduction in mean tumor diameter after treatment. Reduction in tumor enhancement in the arterial phase was statistically significant (P = .01). Tumor ADC value increased from 1.10 × 10^?3 mm²/s to 1.27 × 10^?3 mm²/s after treatment (P < .01), whereas the ADC values for liver and spleen remained unchanged. ADC values from cellular parts of the tumor and necrotic areas also increased after treatment. However, pretreatment ADC values were not reliable to identify responding lesions according to the results of receiver operating characteristic analysis.ConclusionsAfter transarterial chemoembolization, responding HCC lesions exhibited decreases in arterial enhancement and increases in ADC values in cellular and necrotic areas. Pretreatment ADC values were not predictive of response to chemoembolization.     

Irradiated paragangliomas of the head and neck: CT and MR appearance.

PURPOSETo present the spectrum of CT and MR findings of glomus tumors of the head and neck successfully treated with radiation therapy.METHODSThe patient charts and all CT and MR studies of 24 patients (25 tumors) who had been successfully treated with radiation therapy were retrospectively reviewed. Eighteen patients had pre- and posttreatment imaging studies. Tumor size, internal morphology, enhancement pattern, visualization of flow voids, and bone erosion were evaluated before and after radiation therapy. Statistical evaluation of the presence of flows voids and tumor size was performed using the Fischer Exact Test.RESULTSAll patients had residual tumor after radiation therapy. Sixty-one percent of tumors demonstrated a reduction in size. Only one tumor with pretreatment bone destruction demonstrated healing of the bone. MR findings after radiation therapy included variable alteration in T2 signal, decreased heterogeneous enhancement, and a reduction in flow voids. There was a significant difference in the presence of flow voids based on tumor size.CONCLUSIONSSuccessfully irradiated paragangliomas demonstrate residual masses, the presence of which does not by itself indicate treatment failure. Stabilization or reduction in size, decreased enhancement, diminished flow voids, and reduced T2 signal after radiation therapy are a result of therapy and are indicative of local control. Persistent bone demineralization and erosion without progression is commonly seen in successfully controlled tumors. Paragangliomas are relatively homogeneous in internal morphology except for areas of flow void. Flow voids are not a reliable criterion for diagnosis in lesions less than 2.5 cm.     

MR assessment of radiation-induced blood-brain barrier permeability changes in rat glioma model.

PURPOSETo assess the potential of a T1-weighted, gadolinium-enhanced MR technique for quantifying radiation-induced changes of blood-brain barrier permeability in a model of stereotactically implanted intracerebral gliomas in rats.METHODSWe calculated the gadolinium blood-to-tissue transport coefficient for gadopentetate dimeglumine from signal intensities in sequential MR images in nine control animals that were not irradiated and in five and three animals that had received 2500 cGy and 1500 cGy whole-brain irradiation, respectively, at 2 days before imaging.RESULTSThe average blood-to-tissue transport coefficient values were 9.76 mL.kg-1.min-1 in the control group, 23.41 mL.kg-1.min-1 in the 2500 cGy group, and 25.63 mL.kg-1.min-1 in the 1500-cGy group. Blood-to-tissue transport coefficients were significantly higher after irradiation, indicating increased radiation-induced blood-brain barrier permeability. Similar increased blood-brain barrier leakiness in brain tumors after high-dose irradiation has been shown by previous nuclear medicine studies using quantitative autoradiography.CONCLUSIONContrast-enhanced dynamic MR of brain gliomas is a sensitive method to document radiation-induced blood-brain barrier breakdown. Quantitative gadolinium-enhanced MR may become a useful tool for the management of patients with brain tumors undergoing radiation therapy.     

Treatment of brain tumors in children is associated with abnormal MR spectroscopic ratios in brain tissue remote from the tumor site.

PURPOSEChildren who have brain tumors are at risk for a variety of treatment-related sequelae, including neuropsychological and cognitive impairment, neurologic deficits, and neuroendocrinologic disturbances. We sought to determine the value of proton MR spectroscopy in assessing brain tissue remote from the tumor site to ascertain the effects of chemotherapy and radiation treatment in these patients.METHODSSingle-voxel proton MR spectra from 70 patients (111 spectra) and 11 healthy volunteers (11 spectra) were analyzed. NAA/Cr, NAA/Cho, and Cho/Cr ratios based on peak areas were obtained from nonneoplastic regions of the frontal lobe. The relationship between MR spectroscopic ratios and treatment was determined.RESULTSNAA-containing ratios were decreased in patients as compared with control subjects. The presence of gadolinium-based contrast material did not cause significant changes in the ratios as compared with precontrast data. When chemotherapy was a component of a child''s treatment protocol, we found a significant decline in NAA/Cr ratios. Patients who underwent both chemotherapy and radiation therapy showed a trend toward lower NAA-containing ratios if the chemotherapy was administered before the radiation therapy. Patients receiving whole-brain radiation had a trend toward lower NAA-containing ratios than did those who had only focal tumor treatment.CONCLUSIONIn children with brain tumors, MR spectroscopy of brain tissue remote from the tumor reveals treatment-related biochemical changes.     

Differentiation of brain tumor-related edema based on 3D T1rho imaging

Background and purposeCerebral edema associated with brain tumors is an important source of morbidity. Its type depends largely on the capillary ultra-structures of the histopathologic subtype of underlying brain tumor. The purpose of our study was to differentiate vasogenic edema associated with brain metastases and infiltrative edema related to diffuse gliomas using quantitative 3D T1 rho (T1ρ) imaging.Materials and methodsPreoperative MR examination including whole brain 3D T1ρ imaging was performed in 23 patients with newly diagnosed brain tumors (9 with metastasis, 8 with lower grade glioma, LGG, 6 with glioblastoma, GBM). Mean T1ρ values were measured in regions of peritumoral non-enhancing T2 signal hyperintensity, excluding both enhancing and necrotic or cystic component, and normal-appearing white matter.ResultsMean T1ρ values were significantly elevated in the vasogenic edema surrounding intracranial metastases when compared to the infiltrative edema associated with either LGG or GBM (p = 0.02 and <0.01, respectively). No significant difference was noted between T1ρ values of infiltrative edema between LGG and GBM (p = 0.84 and 0.96, respectively).ConclusionOur study demonstrates the feasibility and potential diagnostic role of T1ρ in the quantitative differentiation between edema related to intracranial metastases and gliomas and as a potentially complementary tool to standard MR techniques in further characterizing pathophysiology of vasogenic and infiltrative edema.     

In vivo molecular imaging for planning radiation therapy of gliomas: an application of 1H MRSI

Gliomas are infiltrative lesions that typically have poorly defined margins on conventional magnetic resonance (MR) and computed tomography (CT) images. This presents a considerable challenge for planning radiation and other forms of focal therapy, and introduces the possibility of both under-treating macroscopic tumor, and over-treating regions of normal brain tissue. New therapy systems are able to deliver radiation more precisely and accurately to irregular three-dimensional target volumes, and have placed a premium on definition of the spatial extent of the lesion. Proton MR spectroscopic imaging (H-MRSI) has been proposed as an in vivo molecular imaging technique that assists in targeting and predicts response to radiation therapy for patients with gliomas. The evidence that supports the use of H-MRSI for planning radiation treatment is reviewed, together with the technical requirements for implementing data acquisition and analysis procedures in a clinical setting. Although there is room for improvement in the spatial resolution and chemical specificity obtained at the conventional field strength of 1.5 T, there are clear benefits to integrating H-MRSI into treatment planning and follow-up examinations. Further work is required to integrate the results of the H-MRSI examination into the treatment planning workstation, and to improve the quality of the data using more sensitive phased array coils and higher field strength magnets.     

脑多发胶质瘤影像与病理对照研究

目的 探讨脑多发胶质瘤的影像特点与其病理结果的关系,提高对本病的认识及诊断水平.资料与方法 分析6例经手术病理证实的脑多发胶质瘤的MR及CT影像学资料、病理结果.结果 6例共计13个病灶,MR及CT影像表现为脑内各叶多发肿块样病灶,以额叶最多见,病灶间相互独立.5例影像增强共显示11个病灶,其中7个病灶呈中度至明显强化,病理结果为胶质瘤Ⅲ～Ⅳ级;4个病灶无明显强化,其中2个病灶病理结果为胶质瘤Ⅱ级.结论 脑多发胶质瘤影像表现特征与其病理学类型及分级相关,可初步作出诊断并判断其恶性程度,对临床治疗提供更多帮助.     

Characterization of intracranial mass lesions with in vivo proton MR spectroscopy.

PURPOSETo assess the use of in vivo proton MR spectroscopy for characterization of intracranial mass lesions and to ascertain its reliability in grading of gliomas.METHODSOne hundred twenty patients with intracranial masses were subjected to volume selective spectroscopy using stimulated echo acquisition mode (echo time, 20 and 270 milliseconds) and spin echo (echo time, 135 milliseconds) sequences. The intracranial lesions were grouped into intraaxial and extraaxial, as judged with MR imaging. Assignment of resonances was confirmed in two samples each of brain abscess, epidermoid cyst, and tuberculoma using ex vivo high-resolution MR spectroscopy.RESULTSThe in vivo spectra appeared distinct compared with normal brain in all the cases. All high-grade gliomas (n = 37) showed high choline and low or absent N-acetyl-L-aspartate and creatine along with lipid and/or lactate, whereas low-grade gliomas (n = 23) were characterized by low N-acetyl-aspartate and creatine and high choline and presence of only lactate. N-acetyl-aspartate/choline ratio was significantly lower and choline/creatine ratio was significantly higher in high-grade gliomas than in low-grade gliomas. Presence of lipids suggested a higher grade of malignancy. All metastases (n = 7) showed lipid and lactate, whereas choline was visible in only four cases. Epidermoids showed resonances from lactate and an unassigned resonance at 1.8 ppm. Meningiomas could be differentiated from schwannomas by the presence of alanine in the former. Among the infective masses, pyogenic abscesses (n = 6) showed resonances only from cytosolic amino acids, lactate, alanine, and acetate; and tuberculomas (n = 11) showed only lipid resonances.CONCLUSIONSIn vivo proton MR spectroscopy, helps in tissue characterization of intracranial mass lesions. Spectroscopy is a reliable technique for grading of gliomas when N-acetyl-aspartate/choline and choline/creatine ratios and presence of lipids are used in combination.     

Brain radiation lesions: MR imaging

This retrospective study was performed to assess the capability of magnetic resonance (MR) to depict and characterize diffuse and focal radiation lesions in the brain using the spin-echo technique. The MR images of 55 patients who had undergone radiation therapy were reviewed. Comparative computed tomography (CT) studies were available for all the patients. Normal white matter was chosen as reference tissue for the quantitative comparison of signal intensities. Radiation lesions (identified in eight patients) were seen as regions of high signal intensity on the sequence with a long repetition time (TR) (2.0 sec) and showed no difference in signal compared with white matter when the TR was short (0.5 sec). Nonspecific prolongation of T1 and T2 relaxation times was measured in such lesions. In one patient, subependymal tumor spread, demonstrated by contrast-enhanced CT, was missed on MR images, masked by the adjacent abnormal signal owing to radiation effects. Recurrent or residual brain tumor could not be distinguished from radiation brain necrosis either by CT or by MR imaging. It is concluded that MR can depict radiation lesions with great sensitivity but is not very helpful for discrimination between recurrent or residual brain tumor, radiation necrosis, and other brain lesions.     

Contrast enhancement of brain tumors at different MR field strengths: comparison of 0.5 T and 2.0 T.

PURPOSETo compare the degree of MR contrast enhancement of 0.5 T and 2.0 T in various brain tumors.METHODSMR images were studied prospectively in each of 31 patients with brain tumors (11 gliomas, 6 meningiomas, 6 neurinomas, and 8 others) before and after intravenous injection of gadopentetate dimeglumine. In every patient, both 0.5-T and 2.0-T MR studies were done within 1 week. Each patient received an initial standard dose (0.1 mmol/kg) of gadopentetate dimeglumine, followed by a subsequent 0.1-mmol/kg dose (total, double dose) in MR of each field strength. MR was done before and after each injection of the contrast agent. Degree of contrast enhancement in the lesions was assessed both visually and quantitatively.RESULTSWith standard-dose study, the tumor enhancement was visually stronger at 2.0 T than at 0.5 T in 9 gliomas. In extraaxial tumors there was visually no or minimal difference between 0.5 T and 2.0 T. Overall mean contrast-enhancement ratio and tumor and brain contrast-to-noise ratio were higher at 2.0 T than at 0.5 T by 53% and 108%, respectively. The double-dose study showed higher contrast-enhancement ratio and contrast-to-noise ratio than the standard-dose study at both field strengths, and the differences between 0.5 T and 2.0 T were almost similar to those of the standard-dose study. The degree of contrast enhancement with the standard dose at 2.0 T was comparable to that of the double dose at 0.5 T in most intraaxial tumors.CONCLUSIONThe results suggest that effect of contrast enhancement increases with the field strength. Therefore, reevaluation of optimal doses of contrast media may be needed in a variety of brain lesions at each field strength.     

Multivoxel proton MR spectroscopy and hemodynamic MR imaging of childhood brain tumors: preliminary observations.

PURPOSETo assess multivoxel proton MR spectroscopy combined with MR imaging and hemodynamic MR imaging in the evaluation of brain tumors in children and young adults.METHODSFifteen patients with brain tumors and 10 healthy children underwent MR imaging and MR spectroscopy on a 1.5-T system. Ten patients with tumors had both MR spectroscopy and hemodynamic MR imaging. MR spectroscopy data sets with 1 cm3 to 3.4 cm3 resolution were acquired within 8.5 minutes by using a point-resolved spectroscopic, chemical-shift imaging technique in two dimensions with volume preselection. MR imaging was performed using fast spin-echo techniques. Hemodynamic MR imaging data were acquired every 2.5 seconds at one anatomic level using a spoiled gradient-echo sequence during intravenous bolus administration of contrast material.RESULTSAssessment with multivoxel MR spectroscopy and hemodynamic MR imaging added about 30 minutes to the total MR examination time. Normal tissue exhibited spectral peaks from biologically significant compounds such as N-acetylaspartate (NAA), choline-containing compounds (Cho), and total creatine (tCr). Twelve biopsy-proved tumors exhibited prominent Cho, reduced NAA, variable tCr, and/or lactate or lipids, and two showed increased hemodynamic parameters. Three of the tumors treated with radiation did not reveal prominent levels of Cho. Tissue necrosis had no Cho, NAA, or tCr, and reduced hemodynamics.CONCLUSIONSPreliminary findings by MR spectroscopy combined with MR imaging and hemodynamic MR imaging suggest that regions of active tumor may be differentiated from areas of normal tissue and areas of necrosis. These findings may enable metabolic and hemodynamic characterization of childhood brain tumors as well as suggest their response to therapy.     

Serial proton MR spectroscopic imaging of recurrent malignant gliomas after gamma knife radiosurgery

BACKGROUND AND PURPOSE: The diagnosis of brain tumors after high-dose radiation therapy is frequently limited by the lack of metabolic discrimination available with conventional imaging methods. The purpose of this study was to use proton MR spectroscopy to investigate serial changes in recurrent malignant gliomas after gamma knife radiosurgery to characterize tissue response to high-dose radiation. METHODS: Eighteen patients with recurrent gliomas were studied with MR imaging and 3D proton MR spectroscopic imaging at the time of radiosurgery and at regular time points thereafter. Choline (Cho) and N-acetyl aspartate levels were calculated on a voxel-by-voxel basis and compared with levels found in normal tissue and with levels observed at previous time points. The results of the spectral analysis were then compared with the radiologic findings. Statistical comparisons were precluded by the small sample sizes involved. RESULTS: Response within the gamma knife target was observed as a reduction of Cho levels and an increase in lactate/lipid levels, typically within 6 months of treatment. Increases in Cho correlated with poor radiologic response and suggested tumor recurrence, confirmed histologically in six cases. The development of a spectral abnormality preceded a coincident increase in contrast enhancement by 1 to 2 months in nine cases. CONCLUSION: Proton MR spectroscopic imaging provided diagnostic and monitoring information before and after radiosurgery. Evaluation of metabolic changes with proton MR spectroscopy and structural changes with MR imaging improved tissue discrimination and provided correlation with histologic findings.     

Diffusion-weighted imaging in the follow-up of treated high-grade gliomas: tumor recurrence versus radiation injury

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is a means to characterize and differentiate morphologic features, including edema, necrosis, and tumor tissue, by measuring differences in apparent diffusion coefficient (ADC). We hypothesized that DW imaging has the potential to differentiate recurrent or progressive tumor growth from treatment-induced damage to brain parenchyma in high-grade gliomas after radiation therapy. METHODS: We retrospectively reviewed follow-up conventional and DW MR images obtained starting 1 month after completion of radiation treatment with or without chemotherapy for histologically proved high-grade gliomas. Eighteen patients with areas of abnormal enhancing tissue were identified. ADC maps were calculated from echo-planar DW images, and mean ADC values and ADC ratios (ADC of enhancing lesion to ADC of contralateral white matter) were compared with final diagnosis. Recurrence was established by histologic examination or by clinical course and a combination of imaging studies. RESULTS: Recurrence and nonrecurrence could be differentiated by using mean ADC values and ADC ratios. ADC ratios in the recurrence group showed significantly lower values (mean +/- SD, 1.43 +/- 0.11) than those of the nonrecurrence group (1.82 +/- 0.07, P <.001). Mean ADCs of the recurrent tumors (mean +/- SD, 1.18 +/- 0.13 x 10(-3) mm/s(2)) were significantly lower than those of the nonrecurrence group (1.40 +/- 0.17 x 10(-3) mm/s(2), P <.006). CONCLUSION: Assessment of ADC ratios of enhancing regions in the follow-up of treated high-grade gliomas is useful in differentiating radiation effects from tumor recurrence or progression.     

Breast MR imaging during or soon after radiation therapy

PURPOSE: To investigate the degree and prevalence of radiation-induced changes on breast magnetic resonance (MR) images in patients who were undergoing radiation therapy at that time or soon after, to assess prospectively whether possible radiation-induced effects impair diagnostic accuracy of imaging, and to investigate the prevalence of residual ipsilateral and synchronous contralateral breast cancer in patients undergoing radiation therapy after resection of a supposedly solitary breast cancer. MATERIALS AND METHODS: A total of 116 dynamic bilateral breast MR studies were performed during and up to 12 months after radiation therapy in 72 patients who had undergone breast-conservation surgery without preoperative MR imaging. Patients were assigned to four groups according to the time span between imaging and radiation therapy. Structural changes, parenchymal enhancement pattern, and prevalence and imaging features of incidental lesions were analyzed and compared with those of the nonirradiated breast. RESULTS: Radiation therapy led to parenchymal edema and a significant (two-tailed paired Student t test) increase in enhancement rates in the irradiated compared with those in the contralateral breasts during and up to 3 months after radiation therapy. Neither during nor at any time after radiation therapy did the mean enhancement rates reach diagnostically relevant rates. Unsuspected residual or recurrent breast cancers were identified in irradiated breasts of five patients and in contralateral breasts of two patients. False-positive MR findings resulted in a biopsy in three patients with irradiated and in one patient with nonirradiated breasts. There was no difference in enhancement kinetics or morphology of benign or malignant lesions in irradiated versus nonirradiated breasts. CONCLUSION: Radiation-induced changes occur at MR imaging during or up to 3 months after radiation therapy but are much less severe than reported. Detection and characterization of lesions were feasible with comparable diagnostic accuracies in irradiated and nonirradiated breasts.     

Estimating Local Cellular Density in Glioma Using MR Imaging Data

BACKGROUND AND PURPOSE:Increased cellular density is a hallmark of gliomas, both in the bulk of the tumor and in areas of tumor infiltration into surrounding brain. Altered cellular density causes altered imaging findings, but the degree to which cellular density can be quantitatively estimated from imaging is unknown. The purpose of this study was to discover the best MR imaging and processing techniques to make quantitative and spatially specific estimates of cellular density.MATERIALS AND METHODS:We collected stereotactic biopsies in a prospective imaging clinical trial targeting untreated patients with gliomas at our institution undergoing their first resection. The data included preoperative MR imaging with conventional anatomic, diffusion, perfusion, and permeability sequences and quantitative histopathology on biopsy samples. We then used multiple machine learning methodologies to estimate cellular density using local intensity information from the MR images and quantitative cellular density measurements at the biopsy coordinates as the criterion standard.RESULTS:The random forest methodology estimated cellular density with R² = 0.59 between predicted and observed values using 4 input imaging sequences chosen from our full set of imaging data (T2, fractional anisotropy, CBF, and area under the curve from permeability imaging). Limiting input to conventional MR images (T1 pre- and postcontrast, T2, and FLAIR) yielded slightly degraded performance (R² = 0.52). Outputs were also reported as graphic maps.CONCLUSIONS:Cellular density can be estimated with moderate-to-strong correlations using MR imaging inputs. The random forest machine learning model provided the best estimates. These spatially specific estimates of cellular density will likely be useful in guiding both diagnosis and treatment.

Increased cellular density (CD) is a hallmark of cancer and a key feature in histologic glioma analysis.¹ Mapping cellular density throughout a tumor would be a valuable tool to probe how tumors infiltrate and analyze the transition between diseased and healthy brain. However, measuring CD requires tissue, which entails additional risks and is expensive to obtain. There is no currently accepted clinical algorithm to translate imaging data into quantitative assessments of CD.There is great need for a method to estimate CD noninvasively in human patients with gliomas. In this article, we describe the development of such a method using MR imaging data inputs by correlating with multiple biopsy specimens acquired during a prospective human clinical trial. We obtained comprehensive MR imaging, including conventional, diffusion, perfusion, and permeability imaging sequences. We used machine learning approaches to correlate imaging findings with CD measurements from pathology, devised an algorithm to estimate CD from MR imaging inputs, and generated CD maps for the visual display of the predictions. We identified the most informative imaging data subset. This work has multiple applications in the diagnosis and treatment of patients with gliomas: For example, the method can be used to guide biopsy, resection, and surgery and delineate tumor borderzones both pre- and postoperatively.²     

Cranial MR imaging in neurofibromatosis

Cranial MR images of 53 patients with neurofibromatosis were reviewed to determine the nature, extent, and number of intracranial abnormalities present. All patients studied met tentative definitions established for the diagnosis of neurofibromatosis. Twenty-three were scanned for evaluation of known CNS of cranial nerve involvement; the remainder were neurologically asymptomatic patients without suspected lesions referred for screening. Single lesions were noted in 32 patients. Multiple lesions were identified in 14 patients. Seven had normal scans. In 23 patients small focal areas of increased signal on T2-weighted scans within the brain were though to represent heterotopias. Eight patients had chiasmal gliomas and two had optic nerve gliomas. Nine patients had parenchymal gliomas, two had ischemic changes, and one had a colloid cyst. Extraaxial lesions included acoustic neuromas (five patients), meningiomas (four), trigeminal neurofibromas (one), and dysplasia of a sphenoid wing (two). Of the 30 asymptomatic patients referred for screening, lesions were found in 23. MR was found to be an excellent method of imaging known disease and of detecting lesions in asymptomatic patients. Because of the large number of asymptomatic lesions detected in this population, a screening MR study is recommended in patients with neurofibromatosis.