Temporal lobe necrosis following radiation therapy for nasopharyngeal carcinoma: 1H MR spectroscopic findings

Prognostic and therapeutic evaluation of nasopharyngeal carcinoma by dynamic contrast-enhanced (DCE), diffusion-weighted (DW) magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS)

Nasopharyngeal carcinoma (NPC) is an aggressive head and neck malignancy, and radiotherapy (with or without chemotherapy) is the primary treatment modality. Reliable tumour assessment during the treatment phase, which can portend the efficacy of radiotherapy and early identification of potential treatment failure in radioresistant disease, has been implicit for better cancer management. Technological advancement in the last decade has fostered the development of functional magnetic resonance imaging (fMRI) techniques into a promising tool for diagnostic and therapeutic assessments in head and neck cancer. Apart from conventional morphological assessment, early detection of the physiological environment by fMRI allows a more thorough investigation in monitoring tumour response. This article discusses the relevant fMRI utilities in NPC as an early prognostic and monitoring tool for treatment. Challenges and future developments of fMRI in radiation oncology are also discussed.

Interferon-γ-inducible protein 16 (IFI16) is required for the maintenance of Epstein-Barr virus latency

BACKGROUND

Epstein-Barr virus (EBV) exhibits both lytic and latent (Lat. I, II, and III) phases in an infected individual. It's during the latent phase of EBV that all EBV-associated cancers, including Burkitt's lymphoma, nasopharyngeal carcinoma and lymphoproliferative disease arise. Interferon-γ-inducible protein 16 (IFI16) is a well-established innate immune sensor and viral transcriptional regulator involved in response to invading DNA viruses. During latency, IFI16 remains in the nucleus, in part bound to the EBV genome; however, neither its role in EBV lytic cycle or latency has been established.

METHODS

Short interfering RNA against IFI16 and IFI16 overexpression were used to identify the role of IFI16 in the maintenance of EBV latency I. We also studied how induction of the lytic cycle affected IFI16 using the EBV positive, latently infected Akata or MUTU-1 cell lines. Akata cells were induced with TPA and MUTU-1 cells with TGF-β up to 96 h and changes in IFI16 protein were analyzed by Western blotting and immunofluorescence microscopy. To assess the mechanism of IFI16 decrease, EBV DNA replication and late lytic transcripts were blocked using the viral DNA polymerase inhibitor phosphonoacetic acid.

RESULTS

Knockdown of IFI16 mRNA by siRNA resulted in enhanced levels of EBV lytic gene expression from all temporal gene classes, as well as an increase in the total EBV genome abundance, whereas overexpression of exogenous IFI16 reversed these effects. Furthermore, 96 h after induction of the lytic cycle with either TPA (Akata) or TGF-β (MUTU-1), IFI16 protein levels decreased up to 80% as compared to the EBV-negative cell line BJAB. Reduction in IFI16 was observed in cells expressing EBV lytic envelope glycoprotein. The decreased levels of IFI16 protein do not appear to be dependent on late lytic transcripts of EBV but suggest involvement of the immediate early, early, or a combination of both gene classes.

CONCLUSIONS

Reduction of IFI16 protein levels following lytic cycle induction, as well as reactivation from latency after IFI16 mRNA knockdown suggests that IFI16 is crucial for the maintenance of EBV latency. More importantly, these results identify IFI16 as a unique host factor protein involved in the EBV lifecycle, making it a potential therapeutic target to combat EBV-related malignancies.

Relative cerebral blood volume is a potential biomarker in late delayed radiation-induced brain injury

PURPOSE

To assess whether relative cerebral blood volume (rCBV) can provide information to reliably evaluate the stages of late delayed radiation-induced brain injury.

MATERIALS AND METHODS

Forty patients diagnosed with late delayed radiation-induced brain injury were enrolled. The patients were examined using a 1.5T magnetic resonance imaging (MRI) system equipped with an 8-channel head coil. An echo planar imaging (EPI) sequence was used in perfusion-weighted imaging (PWI). The location of 1H-MR spectroscopy scanning was acquired by a point-resolved spectroscopy sequence. Lesions of the temporal lobe were divided into one of two groups according to rCBV value: rCBV<1 (low rCBV [group 1; n = 45]); and rCBV>1 (elevated rCBV [group 2; n = 14]). PWI and MRS parameters, as well as morphological lesion types, in these two groups were compared. Morphological severity was assessed independently and agreed on by two imaging specialists (J.L. and H.X.S., with 16 and 24 years' experience, respectively). If necessary, a third imaging professor (Z.M.H.) with 30 years' experience resolved disagreement(s). Standards for evaluating morphological lesion types were based on previously published criteria. After testing the skewness of data, the Mann-Whitney U-test or Student's t-test was used, as appropriate.

RESULTS

rCBV, relative cerebral blood flow (rCBF), and relative mean transit time (rMTT) in group 2 (n = 14) were significantly higher than in group 1 (n = 45) (rCBV: 1.21 ± 0.38 vs. 0.72 ± 0.32, respectively; P < 0.001; rCBF: 1.13 ± 0.02 vs. 0.74 ± 0.04, respectively; P < 0.001; rMTT: 1.10 ± 0.26 vs. 0.96 ± 0.20, P < 0.001). The levels of choline-containing compounds (CHO) / creatine (Cr) and CHO/N-acetylaspartate (NAA) in group 1 were significantly greater than in group 2 (CHO/Cr: 1.89 ± 1.83 vs. 1.22 ± 1.31, respectively; P = 0.016; CHO/NAA: 1.85 ± 3.50 vs. 1.17 ± 0.75, respectively; P = 0.022). More severe morphological lesions were present in lesions with low rCBV compared with elevated rCBV (overall severity: 7.00 ± 4.25 vs. 5.00 ± 5.13, respectively; P = 0.029).

CONCLUSION

Elevated rCBV accompanied by a more conservative metabolic pattern and milder lesion(s) may represent a less advanced stage in the development of late delayed radiation-induced brain injury.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1112-1118.

Diffusion kurtosis imaging study on temporal lobe after nasopharyngeal carcinoma radiotherapy

PURPOSE

Diffusion kurtosis imaging (DKI) is a MRI technique which can measure alterations in the diffusion of water molecules to reflect tissue changes in both white and grey matter. This study evaluated the potential of DKI for the early diagnosis of radiation-induced temporal lobe changes in the grey and white matter of the temporal lobe in patients with nasopharyngeal carcinoma (NPC).

MATERIALS AND METHODS

Sixty patients with NPC who had normal MRI brain scans were enrolled and underwent DKI at 1 week (n=20), 6 months (n=20) or 1 year (n=20) after radiotherapy; 20 normal control individuals were also evaluated. Nonlinear fitting routines and equations were used to calculate mean diffusion (MD) and mean kurtosis (MK) and fractional anisotropy (FA). Analysis of variance was used to compare the MK/MD/FA values of white and grey matter between groups.

RESULTS

Compared to the normal control group, grey and white matter MK values were significantly higher at 1 week after radiotherapy and significantly lower at 6 months and 1 year after radiotherapy in patients with NPC, whereas the grey and white matter MD values were significantly lower at 1 week after radiotherapy and returned to normal by 6 months and 1 year after radiotherapy.

CONCLUSION

DKI can be used to detect radiotherapy-induced changes in both the white and grey matter of temporal lobe in patients with NPC. MK and MD values may represent reliable indicators for the early diagnosis of radiation-induced temporal lobe changes in NPC.

Diagnostic Value of Magnetic Resonance Spectroscopy in Radiation Encephalopathy Induced by Radiotherapy for Patients with Nasopharyngeal Carcinoma: A Meta-Analysis

In this study, articles in English and Chinese were selected from available electronic databases prior to September 2014. The metabolic concentrations and patterns of N-acetylaspartic acid (NAA), Choline (Cho), Creatine (Cr), NAA/Cr, NAA/Cho, and Cho/Cr ratios in radiotherapy-induced radiation encephalopathy by proton magnetic resonance spectroscopy were extracted. A meta-analysis was performed to quantitatively synthesize findings of these studies. Weighted mean difference (WMD) and 95% confidence intervals (95%CIs) were calculated using random or fixed effective models. Heterogeneity between studies was assessed using the Cochrane Q test and I (2) statistics. The results indicated that a total of 4 researches involving 214 patients met inclusion criteria. Depending on methodologies of selected studies, control groups were referred to as healthy subjects. The combined analysis revealed that there was no significant difference in value of Cr between radiotherapy group and healthy control group (WMD = -1.483, 95% CI: -67.185-64.219, p = 0.965). However, there were significant difference in values of NAA (WMD = -18.227, 95%CI: -36.317--0.137, p = 0.048), Cho (WMD = 38.003, 95%CI: 5.155-70.851, p = 0.023), NAA/Cr (WMD = -1.175, 95%CI: -1.563--0.787, p = 0.000), NAA/Cho (WMD = -1.108, 95%CI: -2.003-0.213, p = 0.015), and Cho/Cr (WMD = -0.773, 95%CI: 0.239-1.307, p = 0.005). In conclusion, MRS can be regarded as an effective and feasible imaging test for radiotherapy-induced radiation encephalopathy in NPC patients.

Pathophysiology, diagnosis, and treatment of radiation necrosis in the brain

New radiation modalities have made it possible to prolong the survival of individuals with malignant brain tumors, but symptomatic radiation necrosis becomes a serious problem that can negatively affect a patient’s quality of life through severe and lifelong effects. Here we review the relevant literature and introduce our original concept of the pathophysiology of brain radiation necrosis following the treatment of brain, head, and neck tumors. Regarding the pathophysiology of radiation necrosis, we introduce two major hypotheses: glial cell damage or vascular damage. For the differential diagnosis of radiation necrosis and tumor recurrence, we focus on the role of positron emission tomography. Finally, in accord with our hypothesis regarding the pathophysiology, we describe the promising effects of the anti-vascular endothelial growth factor antibody bevacizumab on symptomatic radiation necrosis in the brain.

Differentiating tumor recurrence from treatment necrosis: a review of neuro-oncologic imaging strategies

Differentiating treatment-induced necrosis from tumor recurrence is a central challenge in neuro-oncology. These 2 very different outcomes after brain tumor treatment often appear similarly on routine follow-up imaging studies. They may even manifest with similar clinical symptoms, further confounding an already difficult process for physicians attempting to characterize a new contrast-enhancing lesion appearing on a patient's follow-up imaging. Distinguishing treatment necrosis from tumor recurrence is crucial for diagnosis and treatment planning, and therefore, much effort has been put forth to develop noninvasive methods to differentiate between these disparate outcomes. In this article, we review the latest developments and key findings from research studies exploring the efficacy of structural and functional imaging modalities for differentiating treatment necrosis from tumor recurrence. We discuss the possibility of computational approaches to investigate the usefulness of fine-grained imaging characteristics that are difficult to observe through visual inspection of images. We also propose a flexible treatment-planning algorithm that incorporates advanced functional imaging techniques when indicated by the patient's routine follow-up images and clinical condition.

1H-MR spectroscopy and diffusion tensor imaging of normal-appearing temporal white matter in patients with nasopharyngeal carcinoma after irradiation: initial experience

PURPOSE

To detect radiation-induced changes of temporal lobe normal-appearing white mater (NAWM) following radiation therapy (RT) for nasopharyngeal carcinoma (NPC).

MATERIALS AND METHODS

Seventy-five H(1)-MR spectroscopy and diffusion-tensor imaging (DTI) examinations were performed in 55 patients before and after receiving fractionated radiation therapy (total dose; 66-75GY). We divided the dataset into six groups, a pre-RT control group and five other groups based on time after completion of RT. N-acetylaspartic acid (NAA)/choline (Cho), NAA/creatine (Cr), Cho/Cr, mean diffusibility (MD), functional anisotropy (FA), radial diffusibility (λ(⊥)), and axial diffusibility (λ(||)) were calculated.

RESULTS

NAA/Cho and NAA/Cr decreased and λ(⊥) increased significantly within 1 year after RT compared with pre-RT. After 1 year, NAA/Cho, NAA/Cr, and λ(⊥) were not significantly different from pre-RT. In all post-RT groups, FA decreased significantly. λ(||) decreased within 9 months after RT compared with pre-RT, but was not significantly different from pre-RT more than 9 months after RT.

CONCLUSION

DTI and H(1)-MR spectroscopy can be used to detect early radiation-induced changes of temporal lobe NAWM following radiation therapy for NPC. Metabolic alterations and water diffusion characteristics of temporal lobe NAWM in patients with NPC after RT were dynamic and transient.

Radiation necrosis following treatment of high grade glioma--a review of the literature and current understanding

Radiation therapy is an integral part of the standard treatment paradigm for malignant gliomas, with proven efficacy in randomized control trials. Radiation treatment is not without risk however, and radiation injury occurs in a certain proportion of patients. Difficulties in differentiating recurrence from radiation injury complicate the treatment course and can compromise care. These complexities are compounded by the recent distinction of two types of radiation injury: pseudoprogression and radiation necrosis, which are likely the result of radiation injury to the tumor and normal tissue, respectively. A thorough understanding of radiation-induced injury offers insights to guide further therapies. We detail the current knowledge of the mechanisms of radiation injury, along with potential targets for therapeutic intervention. Various diagnostic modalities are also described, in addition to the multiple options for treatment within the context of their pathophysiology and clinical efficacy. Radiation therapy is an integral part of the multidisciplinary management of gliomas, and the optimal diagnosis and management of radiation injury is paramount to improving patient outcomes.

Diffusion tensor imaging and 1H-MRS study on radiation-induced brain injury after nasopharyngeal carcinoma radiotherapy

AIM

To investigate the metabolic characteristics of the temporal lobes following radiation therapy for nasopharyngeal carcinoma using diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy ((1)H-MRS).

MATERIALS AND METHODS

DTI and (1)H-MRS were performed in 48 patients after radiotherapy for nasopharyngeal carcinoma and in 24 healthy, age-matched controls. All patients and controls had normal findings on conventional MRI. Apparent diffusion coefficient (ADC), fractional anisotropy (FA), three eigenvalues λ1, λ2, λ3, N-acetylaspartic acid (NAA)/choline (Cho), NAA/creatinine (Cr), and Cho/Cr were measured in both temporal lobes. Patients were divided into three groups according to time after completion of radiotherapy: group 1, less than 6 months; group 2, 6-12 months; group 3, more than 12 months. Mean values for each parameter were compared using one-way analysis of variance (ANOVA).

RESULTS

Mean FA in group 1 was significantly lower compared to group 3 and the control group (p < 0.05). Group-wise comparisons of apparent diffusion coefficient (ADC) values among all the groups were not significantly different. Eigenvalue λ1 was significantly lower in groups 1 and 3 compared to the control group (p < 0.05). NAA/Cho and NAA/Cr were significantly lower in each group compared to the control group (p < 0.01 for both). The decrease in NAA/Cho was greatest in group 1. There were no significant between-group differences regarding Cho/Cr.

CONCLUSION

A combination of DTI and (1)H-MRS can be used to detect radiation-induced brain injury, in patients treated for nasopharyngeal carcinoma.

Glioma residual or recurrence versus radiation necrosis: accuracy of pentavalent technetium-99m-dimercaptosuccinic acid [Tc-99m (V) DMSA] brain SPECT compared to proton magnetic resonance spectroscopy (1H-MRS): initial results

We compared pentavalent technetium-99m dimercaptosuccinic acid (Tc-99m (V) DMSA) brain single photon emission computed tomography (SPECT) and proton magnetic resonance spectroscopy ((1)H-MRS) for the detection of residual or recurrent gliomas after surgery and radiotherapy. A total of 24 glioma patients, previously operated upon and treated with radiotherapy, were studied. SPECT was acquired 2-3 h post-administration of 555-740 MBq of Tc-99m (V) DMSA. Lesion to normal (L/N) delayed uptake ratio was calculated as: mean counts of tumor ROI (L)/mean counts of normal mirror symmetric ROI (N). (1)H-MRS was performed using a 1.5-T scanner equipped with a spectroscopy package. SPECT and (1)H-MRS results were compared with pathology or follow-up neuroimaging studies. SPECT and (1)H-MRS showed concordant residue or recurrence in 9/24 (37.5%) patients. Both were true negative in 6/24 (25%) patients. SPECT and (1)H-MRS disagreed in 9 recurrences [7/9 (77.8%) and 2/9 (22.2%) were true positive by SPECT and (1)H-MRS, respectively]. Sensitivity of SPECT and (1)H-MRS in detecting recurrence was 88.8 and 61.1% with accuracies of 91.6 and 70.8%, respectively. A positive association between the delayed L/N ratio and tumor grade was found; the higher the grade, the higher is the L/N ratio (r = 0.62, P = 0.001). Tc-99m (V) DMSA brain SPECT is more accurate compared to (1)H-MRS for the detection of tumor residual tissues or recurrence in glioma patients with previous radiotherapy. It allows early and non-invasive differentiation of residual tumor or recurrence from irradiation necrosis.

Clinical, dosimetric, and radiographic correlation of radiation injury involving the brainstem and the medial temporal lobes following stereotactic radiotherapy for neoplasms of central skull base

Stereotactic Radiotherapy (SRT) is more commonly used for skull base tumors in conjunction with the technical development of radiation intensity modulation. Purpose of this study is to correlate clinical and radiographic characteristics of delayed radiation injury (RI) occurring around central skull base following SRT with SRT dosimetric data. Total of six patients were identified to have developed RI in the vicinity of SRT target volume out of 141 patients who received SRT in he center or near-center of the skull base. The images and medical records were retrospectively reviewed. The analysis was performed for RI location, time of development, imaging and clinical characteristics and evolution of RI and correlated with SRT dosimetric analysis using image fusion with follow-up MRI scans. Mean follow-up time was 24 +/- 9 months. During the follow-up period, twelve sites of RI were found in 6 patients. They were clinically symptomatic in 4/6 patients (66.6%) at median 12.5 months after SRT. Mean time interval between SRT and detection of RI was 9 +/- 3, 18.5 +/- 5, and 13.5 months for brainstem, temporal lobe, and cerebellum/labyrinth lesions, respectively. All RI lesions were included in the region of high SRT doses. After steroid and symptomatic treatment, 50% of RI lesions showed complete response, and 40% showed partial response. RI can occur around the skull base because of irregular shape of target tumor, its close proximity to normal brain parenchyma, and inhomogeneity of dose distribution. Brainstem lesions occurred earlier than temporal lobe RI. The majority of the RI lesions, not mixed with the tumor in this study, showed radiographic and clinical improvement with steroid and symptomatic treatments.

Brain irradiation: effects on normal brain parenchyma and radiation injury

Radiation therapy is a major treatment modality for malignant and benign brain tumors. Concerns of radiation effects on the brain tissue and neurocognitive function and quality of life increase as survival of patients treated for brain tumors improves. In this article, the clinical and neurobehavioral symptoms and signs of radiation-induced brain injury, possible histopathology, and the potential of functional, metabolic, and molecular imaging as a biomarker for assessment and prediction of neurotoxicity after brain irradiation and imaging findings in radiation necrosis are discussed.

MR spectroscopy in radiation injury

Detecting a new area of contrast enhancement in or in the vicinity of a previously treated brain tumor always causes concern for both the patient and the physician. The question that immediately arises is whether this new lesion is recurrent tumor or a treatment effect. The differentiation of recurrent tumor or progressive tumor from radiation injury after radiation therapy is often a radiologic dilemma regardless the technique used, CT or MR imaging. The purpose of this article was to review the utility of one of the newer MR imaging techniques, MR spectroscopy, to distinguish recurrent tumor from radiation necrosis or radiation injury.

Nasopharyngeal carcinoma

Imaging plays an important role in the staging of nasopharyngeal carcinoma. Accurate staging is necessary, as the treatment is directly dependent on stage. Clinical examination provides information on mucosal involvement but is unable to determine the deep extension or the presence of skull base invasion or intracranial spread. The intent of this manuscript is to provide information of the specific imaging findings that will directly affect the stage and treatment of nasopharyngeal carcinoma as well as post-treatment complications.

FIRST-PASS PERFUSION COMPUTED TOMOGRAPHY

OBJECTIVE

To differentiate recurrent tumors from radiation effects and necrosis in patients with irradiated brain tumors using perfusion computed tomographic (PCT) imaging.

METHODS

Twenty-two patients with previously treated brain tumors who showed recurrent or progressive enhancing lesions on follow-up magnetic resonance imaging scans and had a histopathological diagnosis underwent first-pass PCT imaging (26 PCT imaging examinations). Another eight patients with treatment-naïve, high-grade tumors (control group) also underwent PCT assessment. Perfusion maps of cerebral blood volume, cerebral blood flow, and mean transit time were generated at an Advantage Windows workstation using the CT perfusion 3.0 software (General Electric Medical Systems, Milwaukee, WI). Normalized ratios (normalized to normal white matter) of these perfusion parameters (normalized cerebral blood volume [nCBV], normalized cerebral blood flow [nCBF], and normalized mean transit time [nMTT]) were used for final analysis.

RESULTS

Fourteen patients were diagnosed with recurrent tumor, and eight patients had radiation necrosis. There was a statistically significant difference between the two groups, with the recurrent tumor group showing higher mean nCBV (2.65 versus 1.10) and nCBF (2.73 versus 1.08) and shorter nMTT (0.71 versus 1.58) compared with the radiation necrosis group. For nCBV, a cutoff point of 1.65 was found to have a sensitivity of 83.3% and a specificity of 100% to diagnose recurrent tumor and radiation necrosis. Similar sensitivity and specificity were 94.4 and 87.5%, respectively, for nCBF with a cutoff point of 1.28 and 94.4 and 75%, respectively, for nMTT with a cutoff point of 1.44 to diagnose recurrent tumor and radiation necrosis.

CONCLUSION

PCT may aid in differentiating recurrent tumors from radiation necrosis on the basis of various perfusion parameters. Recurrent tumors show higher nCBV and nCBF and lower nMTT compared with radiation necrosis.

Delayed complications of radiotherapy treatment for nasopharyngeal carcinoma: imaging findings

Radiotherapy is used to treat a wide variety of head and neck tumours that arise in and around the skull base. The delayed effects of radiation damages a range of structures, including the nervous system, bone, major vessels, mucus membranes, pituitary and salivary glands, as well as increasing the risk of radiation-induced neoplasms. In this review the complications resulting from radiation treatment for nasopharyngeal carcinoma (NPC), a cancer treated with a high dose of radiation to a fairly large region, are illustrated. Many patients with NPC have a long-term survival, so are at risk of developing delayed radiation effects, and hence may demonstrate a wide range of complications on imaging. Other tumours around the skull base treated with radiotherapy include meningiomas, chordomas, chondrosarcomas, pituitary adenomas, paranasal sinus and nasal cavity tumours. In these cases similar complications may be encountered on imaging, although the severity, incidence and location will vary.

Differentiation of recurrent brain tumor versus radiation injury using diffusion tensor imaging in patients with new contrast-enhancing lesions

BACKGROUND AND PURPOSE

The purpose of this study was to assess the use of diffusion tensor imaging (DTI) in the evaluation of new contrast-enhancing lesions and perilesional edema in patients previously treated for brain neoplasm in the differentiation of recurrent neoplasm from treatment-related injury.

METHODS

Twenty-eight patients with new contrast-enhancing lesions and perilesional edema at the site of previously treated brain neoplasms were retrospectively reviewed. Nine directional echoplanar DTIs with b=1000 s/mm(2) were obtained using a single-shot spin-echo echoplanar imaging. Standardized regions of interest were manually drawn in several regions. Mean apparent diffusion coefficient (ADC), fractional anisotropy (FA) and eigenvalue indices (lambda( parallel) and lambda( perpendicular)) and their ratios relative to the contralateral side were compared in patients with recurrent neoplasm versus patients with radiation injury, as established by histological examination or by clinical course, including long-term imaging studies and magnetic resonance spectroscopy.

RESULTS

The ADC values in the contrast-enhancing lesions were significantly higher (P=.01) for the recurrence group (range=1.01 x 10(-3) to 1.66 x 10(-3) mm(2)/s; mean+/-S.D.=1.27+/-0.15) than for the nonrecurrence group (range=0.9 x 10(-3) to 1.31 x 10(-3) mm(2)/s; mean+/-S.D.=1.12+/-0.14). The ADC ratios in the white matter tracts in perilesional edema trended higher (P=.09) in treatment-related injury than in recurrent neoplasm (mean+/-S.D.=1.85+/-0.30 vs. 1.60+/-0.27, respectively). FA ratios were significantly higher in normal-appearing white matter (NAWM) tracts adjacent to the edema in the nonrecurrence group (mean+/-S.D.=0.89+/-0.15) than in those in the recurrence group (mean+/-S.D.=0.74+/-0.14; P=.03). Both eigenvalue indices lambda( parallel) and lambda( perpendicular) were significantly higher in contrast-enhancing lesions in the recurrence group than in those in the nonrecurrence group (P=.02). As well, both eigenvalue indices lambda( parallel) and lambda( perpendicular) were significantly higher in perilesional edema than in normal white matter (P<.01 and P<.001, respectively) in both groups.

CONCLUSION

The assessment of diffusion properties, especially ADC values and ADC ratios, in contrast-enhancing lesions, perilesional edema and NAWM adjacent to the edema in the follow-up of new contrast-enhancing lesions at the site of previously treated brain neoplasms may add to the information obtained by other imaging techniques in the differentiation of radiation injury from tumor recurrence.

Long-term normal-appearing brain tissue monitoring after irradiation using proton magnetic resonance spectroscopy in vivo: statistical analysis of a large group of patients

PURPOSE

The aim of this study was to detect the non-neoplastic white-matter changes vs. time after irradiation using 1H nuclear magnetic resonance (NMR) spectroscopy in vivo.

METHODS AND MATERIALS

A total of 394 1H MR spectra were acquired from 100 patients (age 19-74 years; mean and median age, 43 years) before and during 2 years after radiation therapy (the mean absorbed doses calculated for the averaged spectroscopy voxels are similar and close to 20 Gy).

RESULTS

Oscillations were observed in choline-containing compounds (Cho)/creatine and phosphocreatine (Cr), Cho/N-acetylaspartate (NAA), and center of gravity (CG) of the lipid band in the range of 0.7-1.5 ppm changes over time reveal oscillations. The parameters have the same 8-month cycle period; however the CG changes precede the other by 2 months.

CONCLUSIONS

The results indicate the oscillative nature of the brain response to irradiation, which may be caused by the blood-brain barrier disruption and repair processes. These oscillations may influence the NMR results, depending on the cycle phase in which the NMR measurements are performed in. The earliest manifestation of radiation injury detected by magnetic resonance spectroscopy is the CG shift.

Physiologic and Metabolic Magnetic Resonance Imaging in Gliomas

Magnetic resonance (MR) imaging provides excellent soft tissue differentiation and in vivo assessment of physiologic and metabolic properties of tissue. As new and more aggressive treatment modalities and combined modalities are being investigated for brain tumor treatment, it is becoming more important to accurately define tumor volumes for treatment planning, to determine the most aggressive tumor regions for intensified radiation treatment, to identify early regional response to therapy for reoptimization of treatment, and to detect early indicators of developing normal tissue toxicity. Readily available MR techniques of physiologic and metabolic imaging can currently provide useful information regarding tumor tissue properties including chemical composition, cerebral blood volume, perfusion, vascular permeability, and water mobility. This article will focus on the potential value of MR physiologic and metabolic imaging in the clinical management of malignant gliomas.

Diffusion Tensor Magnetic Resonance Imaging

Molecular diffusion plays an important role in many biologic phenomena. The ability to study diffusion, therefore, is extremely useful in physiology and medicine. MRI offers a non-invasive window to diffusion, particularly water self-diffusion. MRI techniques, which provide diffusion sensitivity or quantitation (diffusion tensor MRI [DTI]), have found widespread application in neuroscience and medicine, including the evaluation of stroke, brain development, tumor imaging, and demyelinating disorders. We discuss the tensor nature of diffusion and provide an overview of how DTI offers unique information on tissue organization, water mobility, and disease states, particularly those of neuro-ophthalmologic interest.

Differentiation between brain tumor recurrence and radiation injury using MR spectroscopy

OBJECTIVE

The purpose of our study was to explore the feasibility and utility of 2D chemical shift imaging (CSI) MR spectroscopy in the evaluation of new areas of contrast enhancement at the site of a previously treated brain neoplasm.

MATERIALS AND METHODS

Two-dimensional CSI (point-resolved spectroscopy sequence [PRESS]; TR/TE, 1,500/144) was performed in 29 consecutive patients (4-54 years old; mean age, 34 years) who had a new contrast-enhancing lesion in the vicinity of a previously diagnosed and treated brain neoplasm. Clinical and imaging follow-up, and histopathology in 16 patients, were used as indicators of the identity of a lesion.

RESULTS

Diagnostic-quality spectra were obtained in 97% of the patients. The Cho/Cr (choline/creatine) and Cho/NAA (choline/N-acetyl aspartate) ratios were significantly higher, and the NAA/Cr ratios significantly lower, in tumor than in radiation injury (all three differences, p < 0.0001). The Cho/Cr and Cho/NAA ratios were significantly higher in radiation injury than in normal-appearing white matter (p < 0.0003 and p < 0.0001, respectively), whereas NAA/Cr ratios were not different (p = 0.075). Mean Cho/Cr ratios were 2.52 for tumor, 1.57 for radiation injury, and 1.14 for normal-appearing white matter. Mean Cho/NAA ratios were 3.48, 1.31, 0.79, and mean NAA/Cr ratios were 0.79, 1.22, and 1.38, respectively. When values greater than 1.8 for either Cho/Cr or Cho/NAA ratios were considered evidence of tumor, 27 of 28 patients could be correctly classified.

CONCLUSION

Two-dimensional CSI MR spectroscopy can differentiate tumor from radiation injury in patients with recurrent contrast-enhancing intracranial lesions. In these lesions, the Cho/NAA and Cho/Cr ratios may be the best numeric discriminators.

Post treatment imaging in head and neck tumours

Cancer is a leading cause of death in most parts of the world. Most patients will undergo multiple imaging studies following treatment. The regular follow up of these patients often leads to the early detection of tumour recurrence or the onset of treatment complications. Early diagnosis may result in the timely institution of appropriate therapy thereby improving the survival and morbidity rates. This review addresses difficulties related to demonstrating early tumour recurrence and nodal metastasis and focuses on the complications seen in the central nervous system, cranial nerves and brachial plexus following radiotherapy.

Imaging of neoplasms of the paranasal sinuses

The assessment of sinonasal malignancies requires a multidisciplinary team approach.Advances in pretherapeutic imaging have significantly contributed to the managementof sinonasal tumors. CT and MR imaging play complementary roles in the assess-mentand staging of these malignancies by determining the presence or absence of exten-sionof disease into the skull base and its foramina, the orbit, and the intracranial compartment.

Investigation of metabolic changes in irradiated rat brain tissue by means of 1H NMR in vitro relaxation study

The effect of irradiation on concentrations and relaxation behaviour of brain metabolites was studied by means of high-resolution 1H NMR in vitro. The studies were performed on rat brains irradiated with the doses of 20 Gy applied in fractions of 2 Gy. Standard procedures were used to obtain HClO4 extracts of rat brains. The 1H NMR studies of the extracts solutions in D2O were performed using a Varian Inova-300 NMR spectrometer. The integral intensities of the metabolite signals were found to change during the irradiation cycle and after it. These changes are accompanied by the variations in the T1 relaxation times. N-acetylaspartate, glycerophosphocholine, phosphocholine, choline, creatine and phosphocreatine, myoinositol and taurine were analysed as potential markers of irradiation injury.

1H-MR spectroscopy of normal brain tissue before and after postoperative radiotherapy because of primary brain tumors

PURPOSE

Brain metabolism after surgery and postoperative radiotherapy (pRT) because of primary brain tumors was assessed by proton magnetic resonance spectroscopy ((1)H-MRS) in vivo. The study was designed to reveal the impact of pRT on normal brain tissue metabolism, which may potentially help in delineating the target volumes for reirradiated patients.

METHODS AND MATERIALS

Spectra of 43 patients ages 16-63 years treated with pRT for primary glial tumors in the Center of Oncology Maria Curie Memorial Institute Branch in Gliwice were analyzed. The control group consisted of spectra acquired for 30 healthy volunteers. All patients were treated with 3D conformal techniques using 6-20 MV photons to total doses of 60 Gy. Spectra were acquired from the control region before pRT and from three uninvolved regions 9-12 months after the end of pRT. Voxels were located in the region of low (<6 Gy), medium (29-39 Gy), and high radiation dose ( approximately 60 Gy). Relative intensities of the signals relating to N-acetyl-aspartate (NAA), choline-based compounds, creatine and phosphocreatine (Cr), mio-Inositol, lactate, and lipids were obtained.

RESULTS

The spectra of "normal brain" taken 9 months after pRT are significantly different from those obtained for control volunteers and from the spectra acquired before radiotherapy. The lactate and lipids signals are very strong; however, they are not correlated with absorbed dose. NAA/Cr ratios are significantly lower than before radiotherapy even for the low-dose regions. Differences increase with radiation dose: the NAA/Cr ratio is significantly lower for the regions of brain receiving a high dose of radiation than for the low-dose areas.

CONCLUSION

Combined treatment of primary brain tumors (surgery + postoperative radiotherapy) causes alteration of brain metabolism, even in regions of the brain far from the postoperative tumor bed and receiving relatively low total doses of radiation. Single voxel MRS spectroscopy in vivo cannot help in delineating target volumes for secondary irradiation.

In vivo 3-T MR spectroscopy in the distinction of recurrent glioma versus radiation effects: initial experience

PURPOSE

To determine if 3-T magnetic resonance (MR) spectroscopy allows accurate distinction of recurrent tumor from radiation effects in patients with gliomas of grade II or higher.

MATERIALS AND METHODS

This blinded prospective study included 14 patients who underwent in vivo 3-T MR spectroscopy prior to stereotactic biopsy. All patients received a previous diagnosis of glioma (grade II or higher) and high-dose radiation therapy (>54 Gy). Prior to MR spectroscopy, conventional MR imaging was performed at 1.5 T to identify a gadolinium-enhanced region within the irradiated volume. Diagnosis was assigned by means of histopathologic analysis of the biopsy samples.

RESULTS

Sixteen of 17 biopsy locations could be classified as predominantly tumor or predominantly radiation effect on the basis of the ratio of choline at the biopsy site to normal creatine level by using a value greater than 1.3 as the criterion for tumor. The remaining case, classified as recurrent tumor on the basis of MR spectroscopy results, was diagnosed as predominantly radiation effect on the basis of histopathologic findings. Disease in this patient progressed to biopsy-proven recurrence within 3 months. Overall, the ratio of choline at the biopsy site to normal creatine level was significantly elevated (unpaired two-tailed Student t test, P <.002) in those biopsy samples composed predominantly of tumor (n = 9) compared with those containing predominantly radiation effects (n = 8). The ratio was not significantly different between the two histopathologic groups.

CONCLUSION

In vivo 3-T MR spectroscopy has sufficient spatial resolution and chemical specificity to allow distinction of recurrent tumor from radiation effects in patients with treated gliomas.

Neurological changes following radiation therapy for head and neck tumours

Radiation therapy is widely used in the treatment of head and neck tumours either as a primary form of treatment or a supplementary modality. Although the benefits of radiation therapy are well established, this treatment modality is not without untoward consequences and complications. The intent of this paper is to highlight the neurological complications that may follow the treatment for head and neck malignancies, in particular, following radiation therapy for nasopharyngeal carcinoma.

Posttreatment imaging of the nasopharynx

Nasopharyngeal carcinoma (NPC) is the most common epithelial tumor of the nasopharynx. Radiation therapy is the mainstay of treatment while surgery or chemotherapy is used in selected patients. NPC usually regresses after 3 months of radiation therapy. Nonetheless, a residual mass may be present following treatment and this does not necessarily indicate viable tumor. Imaging studies are often used in conjunction with clinical examination following treatment. While computed tomography (CT) is widely used due to its greater availability, less expensive, and less time consuming, MR imaging is now becoming the preferred modality. MR imaging is more capable than CT for identifying mature scarring, tumor recurrence and postradiation complications. However, MR imaging cannot reliably demonstrate mucosal recurrence or differentiate tumor recurrence from postradiation tissue changes. Familiarity with the imaging findings of various posttreatment changes, tumor recurrence and postradiation complications is essential for management of NPC. Comparison with previous images or imaging-guided biopsy facilitates definitive diagnosis.

Concomitant diminishing magnetization-transfer effect and increasing choline level in radiation-induced temporal-lobe changes

This article reports on the use of both magnetization-transfer (MT) imaging and 1H-MR spectroscopy in two cases of bilateral temporal-lobe changes after radiation therapy for nasopharyngeal carcinoma. In the first case, the following patterns were noted: (i) although the temporal lobes appeared relatively normal on T2-weighted MR imaging, corresponding MT imaging clearly showed signal abnormalities (decreased MT effect) consistent with alterations in macromolecular structure; and (ii) concomitant strongly elevated choline on 1H-MR spectroscopy was observed, and this is associated with metabolic changes in cell membranes. The second case presented similar characteristics. In addition, there was an increased lactate signal and T2 signal changes in keeping with established oedema. Both MT and proton-spectroscopic findings were consistent with postulated pathophysiological features of radiation injury, but their specificity for this condition remains unclear. Magnetization-transfer imaging, and possibly 1H-MR spectroscopy, might be sensitive techniques for the early detection of late radiation injury.

Imaging of neoplasms of the paranasal sinuses

The assessment of sinonasal malignancies requires a multidisciplinary team approach. Advances in pretherapeutic imaging have significantly contributed to the management of sinonasal tumors. CT and MR imaging play complementary roles in the assessment and staging of these malignancies by determining the presence or absence of extension of disease into the skull base and its foramina, the orbit, and the intracranial compartment.

Detection of an intense resonance at 2.4 ppm in 1H MR spectra of patients with severe late-delayed, radiation-induced brain injuries

Proton MRS and MRI were used to monitor the progression of severe cerebral radiation injuries in 10 patients over a period of 18 months. An unknown resonance (Px) in the 2.37-2.40 ppm region was consistently detected in the affected temporal lobes of four patients. The detection of Px was only confined to spectra with lactate (Lac) and in patients with the highest severity grading of radiation injury. The incidence of Px in Lac-positive spectra was 42.8% (15/35) and in lesions with highest injury grading was 46.8% (15/32). Lesions with Px had significantly higher Lac/creatine (Cr) ratios and more extensive mass effect changes when compared to lesions without Px. The probable identity of Px was examined in the context of anaerobic glycolysis producing pyruvate (2.37 ppm) and the model of metabolic changes in brain abscess formation implicating succinate (2.40 ppm).

Automatic quantitation of localized in vivo 1H spectra with LCModel

The LCModel method analyzes an in vivo spectrum as a Linear Combination of Model in vitro spectra from individual metabolite solutions. Complete model spectra, rather than individual resonances, are used in order to incorporate maximum prior information into the analysis. A nearly model-free constrained regularization method automatically accounts for the baseline and lineshape in vivo without imposing a restrictive parameterized form on them. LCModel is automatic (non-interactive) with no subjective input. Approximately maximum-likelihood estimates of the metabolite concentrations and their uncertainties (Cramér-Rao lower bounds) are obtained. LCModel analyses of spectra from users with fields from 1.5 to 9.4 T and a wide range of sequences, particularly with short TE, are used here to illustrate the capabilities and limitations of LCModel and proton MRS.

Radiation-induced temporal lobe changes: CT and MR imaging characteristics

OBJECTIVE

This article documents the CT and MR imaging characteristics of patients with temporal lobe changes after radiation therapy for nasopharyngeal carcinoma. These characteristics may serve to differentiate radiation-induced changes from intracranial tumor recurrence.

MATERIALS AND METHODS

We reviewed the imaging records of 1916 patients with nasopharyngeal carcinoma examined over a 5-year period. Forty-seven patients (2.5%) had temporal lobe changes. Thirty-four patients underwent CT (55 examinations), and 26 patients underwent MR imaging (32 examinations). Thirteen patients underwent CT and MR imaging. These studies were independently analyzed according to imaging technique and were categorized as follows: location of lesions, characteristics of gray or white matter changes, and patterns of late changes.

RESULTS

On CT, 12 patients (35%) had unilateral temporal lobe changes, and 22 patients (65%) had bilateral temporal lobe changes. The following patterns were noted: ill-defined contrast enhancement in 27 patients (79%); solid enhancement in six patients (18%); and ring enhancement in one patient (3%). On MR imaging, 11 patients (42%) had unilateral lesions, and 15 patients (58%) had bilateral lesions. Simultaneous gray and white matter lesions were noted in 17 patients (65%), and nine patients (35%) had lesions localized to the gray matter. Three patients (6%) had cerebral atrophy, and two patients (4%) had encephalomalacia.

CONCLUSION

The temporal lobes show characteristic CT and MR imaging features after radiation injury. Familiarity with these changes may assist in differentiating temporal lobe changes from progressive nasopharyngeal carcinoma.