Quantitative MRI assessment of leukoencephalopathy

Modified Diffusion Tensor Image Processing Pipeline for Archived Studies of Patients With Leukoencephalopathy

BACKGROUND

In archived diffusion tensor imaging (DTI) studies, a reversed-phase encoding (PE) scan required to correct the distortion in single-shot echo-planar imaging (EPI) may not have been acquired. Furthermore, DTI tractography is adversely affected by incorrect white matter segmentation due to leukoencephalopathy (LE). All these issues need to be addressed.

PURPOSE

To propose and evaluate a modified DTI processing pipeline with DIstortion COrrection using pseudo T₂ -weighted images (DICOT) to overcome limitations in existing acquisition protocols.

STUDY TYPE

Retrospective feasibility.

SUBJECTS

DICOT was assessed in simulated data and 84 acute lymphoblastic leukemia (ALL) patients with reversed PE acquired. The pipeline was then tested in 522 scans from 261 ALL patients without a reversed PE acquired.

FIELD STRENGTH/SEQUENCE

A 3 T; diffusion-weighted EPI; 3D magnetization prepared rapid acquisition gradient echo (MPRAGE).

STATISTICAL TESTS

Repeated measures analysis of variance and Tukey post hoc tests were performed to compare fractional anisotropy (FA) values obtained by different methods.

ASSESSMENT

FA and corresponding absolute error maps were obtained using TOPUP, DICOT, INVERSION (Inverse contrast Normalization for VERy Simple registratION) and NO CORR (no correction). Each method was assessed by comparing to TOPUP. The pipeline in the ALL patients was evaluated based on the failure rate of the distortion correction using the global correlation values.

RESULTS

Using DICOT reduced the mean absolute errors by an average of 32% in FA in simulation datasets. In 84 patients, the error reductions were approximately 15% in FA with DICOT, while it was 5% with INVERSION. No significant differences between the TOPUP and DICOT were observed in FA with P = 0.090/0.894(AP/PA). Only 15 of 516 examinations requiring any additional manual intervention.

CONCLUSION

This modified pipeline produced better results than the INVERSION. Furthermore, robust performance was demonstrated in archived patient scans acquired without an inverse PE necessary for TOPUP correction.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

Regional brain glucose metabolism and neurocognitive function in adult survivors of childhood cancer treated with cranial radiation

The objective of this study was to examine associations between regional brain metabolism, as measured by (18)F-FDG PET, and neurocognitive outcomes in adult survivors of childhood acute lymphoblastic leukemia (ALL) treated with cranial radiation.

METHOD

Thirty-eight adult survivors of ALL were randomly selected from a large cohort treated with cranial radiation therapy (19 with 18 Gy and 19 with 24 Gy of exposure). At a mean age of 26.4 (range, 22.3-37.4) years, and 23.5 (range, 20.4-32.8) years since diagnosis, patients underwent comprehensive neurocognitive evaluations and brain (18)F-FDG PET imaging during a resting condition. (18)F-FDG PET images were analyzed stereotactically, and pixel values were normalized to global activity. Predefined region-of-interest and voxel-based correlation analyses were performed.

RESULTS

Compared with national norms, survivors demonstrated lower vocabulary (P < 0.001), reading (P < 0.001), mathematics (P < 0.001), working memory (P < 0.001), oral naming speed (P < 0.001), and cognitive flexibility (P < 0.001). Metabolic activity was higher in basal gangliar structures for those treated with 24 Gy of cranial radiation therapy (P = 0.04). Metabolic activity was positively correlated with oral naming speed in both lateral frontal lobes (ρ = 0.48 and 0.47 for right and left frontal regions, respectively, P < 0.01) and negatively correlated with cognitive flexibility in the sections of the basal ganglia (P < 0.01 for both caudate and putamen).

CONCLUSION

Neurocognitive impairment in long-term survivors of ALL treated with cranial radiation appears to be associated with increased metabolic activity in frontal cerebral cortical and subcortical regions in the basal ganglia, suggesting decreased efficiency of the frontostriatal brain circuit.

The relationship between working memory and cerebral white matter volume in survivors of childhood brain tumors treated with conformal radiation therapy

Survivors of childhood brain tumors (BTs) treated with CNS-directed therapy show changes in cerebral white matter that are related to neurocognitive late effects. We examined the association between white matter volume and working memory ability in survivors treated with conformal radiation therapy (CRT). Fifty survivors (25 males, age at assessment = 13.14 ± 2.88, age at CRT = 7.41 ± 3.41 years) completed Digit Span from the Wechsler Intelligence Scales for Children, 4th Edition and experimental Self-Ordered Search (SOS) tasks as measures of working memory. Caregiver ratings were obtained using the Behavior Rating Inventory of Executive Function. MRI exams were acquired on a 1.5 T scanner. Volumes of normal appearing white matter (NAWM) were quantified using a well-validated automated segmentation and classification program. Correlational analyses demonstrated that NAWM volumes were significantly larger in males and participants with tumors located in the infratentorial space. Correlations between NAWM volume and Digit Span Backward were distributed across anterior and posterior regions, with evidence for greater right hemisphere involvement (r = .32-.34, p ≤ .05). Correlations between NAWM volume with Digit Span Backward (r = .44-.52; p ≤ .05) and NAWM volume with SOS-Object Total (r = .45-.52, p ≤ .05) were of greater magnitude in females. No relationship was found between NAWM volume and caregiver report. Working memory performance in survivors of pediatric BTs treated with CRT are related to regionally specific NAWM volume. Developmental differences in cerebral myelination may explain findings of greater risk for neurocognitive late effects in female survivors. Future studies are needed to better isolate vulnerable white matter pathways, thus facilitating the development of neuroprotective interventions.

Evaluation of memory impairment in aging adult survivors of childhood acute lymphoblastic leukemia treated with cranial radiotherapy

BACKGROUND

Cranial radiotherapy (CRT) is a known risk factor for neurocognitive impairment in survivors of childhood cancer and may increase risk for mild cognitive impairment and dementia in adulthood.

METHODS

We performed a cross-sectional evaluation of survivors of childhood acute lymphoblastic leukemia (ALL) treated with 18 Gy (n = 127) or 24 Gy (n = 138) CRT. Impairment (age-adjusted score >1 standard deviation below expected mean, two-sided exact binomial test) on the Wechsler Memory Scale IV (WMS-IV) was measured. A subset of survivors (n = 85) completed structural and functional neuroimaging.

RESULTS

Survivors who received 24 Gy, but not 18 Gy, CRT had impairment in immediate (impairment rate = 33.8%, 95% confidence interval [CI] = 25.9% to 42.4%; P < .001) and delayed memory (impairment rate = 30.2%, 95% CI = 22.6% to 38.6%; P < .001). The mean score for long-term narrative memory among survivors who received 24 Gy CRT was equivalent to that for individuals older than 69 years. Impaired immediate memory was associated with smaller right (P = .02) and left (P = .008) temporal lobe volumes, and impaired delayed memory was associated with thinner parietal and frontal cortices. Lower hippocampal volumes and increased functional magnetic resonance imaging activation were observed with memory impairment. Reduced cognitive status (Brief Cognitive Status Exam from the WMS-IV) was identified after 24 Gy (18.5%, 95% CI = 12.4% to 26.1%; P < .001), but not 18 Gy (8.7%, 95% CI = 4.4% to 15.0%; P = .11), CRT, suggesting a dose-response effect. Employment rates were equivalent (63.8% for 24 Gy CRT and 63.0% for 18 Gy CRT).

CONCLUSIONS

Adult survivors who received 24 Gy CRT had reduced cognitive status and memory, with reduced integrity in neuroanatomical regions essential in memory formation, consistent with early onset mild cognitive impairment.

The impact of therapy for childhood acute lymphoblastic leukaemia on intelligence quotients; results of the risk-stratified randomized central nervous system treatment trial MRC UKALL XI

Background

The MRC UKALLXI trial tested the efficacy of different central nervous system (CNS) directed therapies in childhood acute lymphoblastic leukaemia (ALL). To evaluate morbidity 555/1826 randomised children underwent prospective psychological evaluations. Full Scale, verbal and performance IQs were measured at 5 months, 3 years and 5 years. Scores were compared in; (1) all patients (n = 555) versus related controls (n = 311), (2) low-risk children (presenting white cell count (WCC) < 50 × 10⁹/l) randomised to intrathecal methotrexate (n = 197) versus intrathecal and high-dose intravenous methotrexate (HDM) (n = 202), and (3) high-risk children (WCC ≥ 50 × 10⁹/l, age ≥ 2 years) randomised to HDM (n = 79) versus cranial irradiation (n = 77).

Results

There were no significant differences in IQ scores between the treatment arms in either low- or high-risk groups. Despite similar scores at baseline, results at 3 and 5 years showed a significant reduction of between 3.6 and 7.3 points in all three IQ scores in all patient groups compared to controls (P < 0.002) with a higher proportion of children with IQs < 80 in the patient groups (13% vs. 5% at 3 years p = 0.003).

Conclusion

Children with ALL are at risk of CNS morbidity, regardless of the mode of CNS-directed therapy. Further work needs to identify individuals at high-risk of adverse CNS outcomes.

Trial registration

ISRCTN: ISRCTN16757172

Attention and working memory abilities in children treated for acute lymphoblastic leukemia

BACKGROUND

To extend investigation beyond global cognitive measures prevalent in the literature, this study examined attention and working memory (WM) abilities of survivors of childhood acute lymphoblastic leukemia (ALL), the separate contributions of attention and WM to intelligence quotient (IQ), and their association with neuroimaging changes.

METHODS

Ninety-seven children with ALL received risk-directed therapy based on presenting clinical and biological factors. During consolidation therapy, low-risk patients received half the dose of intravenous methotrexate that standard-risk/high-risk patients received, and fewer doses of triple intrathecal therapy. Patients were classified according to end of consolidation magnetic resonance imaging scans (normal or leukoencephalopathy), and continuous measures of white matter structure were computed. As part of the protocol study, children completed cognitive assessment 2 years later (completion of therapy), using Digit Span Forward (DSF) for attention and Digit Span Backward (DSB) for WM.

RESULTS

For the total sample and the standard-/high-risk group, Total Digit Span (TDS), DSF, and DSB were impaired relative to norms (P<.05). In the low-risk group, only DSB was impaired (P<.0001). Across groups, a higher percentage of patients performed below the average range (scale score<7) on DSB (66%) compared with the DSF (14%) or TDS (18%). Regression analysis indicated that DSB predicted estimated IQ (P<.05), after accounting for DSF. Leukoencephalopathy was predictive of lower TDS (P<.05).

CONCLUSIONS

WM appears to be especially sensitive to treatment-related changes in ALL survivors, detecting difficulties potentially missed by global intelligence measures. These findings may facilitate the identification of vulnerable neural pathways and the development of targeted cognitive interventions.

Cerebellocerebral diaschisis is the likely mechanism of postsurgical posterior fossa syndrome in pediatric patients with midline cerebellar tumors

BACKGROUND AND PURPOSE

PFS occurs in approximately 25% of pediatric patients receiving surgery for midline posterior fossa tumors. Increasing evidence suggests that PFS represents a complex supratentorial cortical dysfunction related to surgery-induced disruption of critical cerebellocerebral connections. The purpose of this study was to determine whether a consistent surgical damage pattern may be identified in patients with PFS by early postoperative anatomic imaging analysis of the pECP and to test whether DSC can detect corresponding changes in cerebral cortical perfusion to indicate a secondary, remote functional disturbance, which could suggest a diaschisis-like pathomechanism.

MATERIALS AND METHODS

Eleven patients with postoperative PFS were evaluated retrospectively and were paired with age- and sex-matched control subjects in whom PFS did not develop. MR imaging work-up included DSC within 3 to 4 weeks after surgery as well as early postoperative anatomic imaging to evaluate components of the pECP.

RESULTS

DSC showed significant decreases in CBF within frontal regions (P < .05) and a trend to global cerebral cortical hypoperfusion in patients with PFS. Logistic regression analysis suggested a strong (potentially predictive) relationship between bilateral damage to pECP and the development of PFS (P = .04).

CONCLUSIONS

Our data suggest that the primary cause of PFS is the bilateral surgical damage to the pECP. This leads to a trans-synaptic cerebral cortical dysfunction (a form of bilateral crossed cerebellocerebral diaschisis), which manifests with DSC-detectable global, but dominantly frontal, cortical hypoperfusion in patients with patients with PFS compared with age- and sex-matched control subjects.

Multiple factors contribute to neuropsychological outcome in children with posterior fossa tumors

Cognitive deficits are frequently reported in children treated for posterior fossa (PF) tumors. A range of tumor, treatment, medical and treatment complications have been implicated in causing a variety of cognitive deficits. The aim of this study is to identify factors that influence intelligence, attention and information processing in these children. Thirty-five children (aged 4-16) with PF tumors attending the Royal Children's Hospital Melbourne, Australia, were enrolled into a prospective, repeated measures design. Neuropsychological assessments were conducted at diagnosis and at 12 month intervals for three years. The results find that the PF tumor, hydrocephalus, white matter injury and radiation therapy have various impacts on intelligence, attention and information processing skills, and contribute to the long term outcome in children treated for PF tumor. The neurological structures that subserve the efficient function of attention and information processing are particularly vulnerable to those factors.

Quantitative morphologic evaluation of magnetic resonance imaging during and after treatment of childhood leukemia

INTRODUCTION

Medical advances over the last several decades, including CNS prophylaxis, have greatly increased survival in children with leukemia. As survival rates have increased, clinicians and scientists have been afforded the opportunity to further develop treatments to improve the quality of life of survivors by minimizing the long-term adverse effects. When evaluating the effect of antileukemia therapy on the developing brain, magnetic resonance (MR) imaging has been the preferred modality because it quantifies morphologic changes objectively and noninvasively.

METHOD AND RESULTS

Computer-aided detection of changes on neuroimages enables us to objectively differentiate leukoencephalopathy from normal maturation of the developing brain. Quantitative tissue segmentation algorithms and relaxometry measures have been used to determine the prevalence, extent, and intensity of white matter changes that occur during therapy. More recently, diffusion tensor imaging has been used to quantify microstructural changes in the integrity of the white matter fiber tracts. MR perfusion imaging can be used to noninvasively monitor vascular changes during therapy. Changes in quantitative MR measures have been associated, to some degree, with changes in neurocognitive function during and after treatment.

CONCLUSION

In this review, we present recent advances in quantitative evaluation of MR imaging and discuss how these methods hold the promise to further elucidate the pathophysiologic effects of treatment for childhood leukemia.

Quantitative morphologic evaluation of white matter in survivors of childhood medulloblastoma

In survivors of pediatric brain tumors, cranial radiation therapy can cause a debilitating cognitive decline associated with decreased volume in normal-appearing white matter (NAWM). We applied fractal geometry to quantify white matter (WM) integrity in the brain of medulloblastoma survivors. Fractal features of WM were evaluated by indices of fractal dimensions (FDs) of WM intensity and boundary on T1-weighted magnetic resonance images. The FD index of WM intensity was calculated by using a fractional Brownian motion model, and the FD index of WM boundary was calculated by using a box-counting method. Fractal features of WM on 116 magnetic resonance images of 58 patients with medulloblastoma were investigated at the start of therapy (Start TX) and approximately 2 years later (After TX). Patients were assigned to one of two groups based on change in NAWM volumes. Fractal features in patients with decreased NAWM volume were significantly greater After TX, whereas those in patients with increased NAWM volumes were not. Multiple linear regression analysis showed that fractal features were strongly correlated with NAWM volumes After TX in patients with decreased NAWM volume. These results demonstrated significant deficit in NAWM integrity and WM density changes in children treated for medulloblastoma. Multiple regression analysis illustrated that deficits in NAWM integrity in these children may partly explain the decrease in NAWM volume. We conclude that fractal geometry can be used to monitor the morphologic effects of neurotoxicity in brain tumor survivors.

Delayed neurotoxicity associated with therapy for children with acute lymphoblastic leukemia

Most children diagnosed today with acute lymphoblastic leukemia (ALL) will be cured. However, treatment entails risk of neurotoxicity, causing deficits in neurocognitive function that can persist in the years after treatment is completed. Many of the components of leukemia therapy can contribute to adverse neurologic sequelae, including craniospinal irradiation, nucleoside analogs, corticosteroids, and antifolates. In this review, we describe the characteristic radiographic findings and neurocognitive deficits seen among survivors of childhood ALL. We summarize what is known about the pathophysiology of delayed treatment-related neurotoxicity, with a focus on the toxicity resulting from pharmacologic disruption of folate physiology within the central nervous system. Finally, we suggest testable strategies to ameliorate the symptoms of treatment-related neurotoxicity or decrease its incidence.

A quantitative MR imaging assessment of leukoencephalopathy in children treated for acute lymphoblastic leukemia without irradiation

PURPOSE

Intravenous methotrexate (IV-MTX), an effective treatment for acute lymphoblastic leukemia (ALL), has a significant toxic effect on the central nervous system, with leukoencephalopathy (LE) being the most common form. The purpose of this study was to use objective quantitative MR imaging to prospectively assess the temporal evolution of LE extent and intensity.

METHODS

Forty-five children (low-risk, 10 mol/L/12F; mean age, 5.0 years at diagnosis; standard/high-risk, 11 mol/L/12F; mean age, 9.2 years at diagnosis) treated for ALL on a single institutional protocol were evaluated longitudinally to assess the extent of LE (proportion of white matter impacted) through tissue segmentation and the relative intensity of LE through relative elevations in T1 and T2 relaxation rates. One-sided Wilcoxon-Mann-Whitney tests were used to assess differences in quantitative measures at 4 different points in therapy both within and between risk arms.

RESULTS

The proportion of white matter affected in both patient groups increased significantly with additional courses of IV-MTX, whereas the intensity of LE also increased steadily; however, both the intensity and extent of LE declined significantly approximately 1.5 years after completion of IV-MTX. Increases in the T1 and T2 relaxation rates above normal-appearing white matter were significantly correlated with each other and were dependent on the proportion of white matter affected.

CONCLUSION

Higher doses and more courses of IV-MTX were associated with increased intensity and extent of LE. There was a significant reduction in both the intensity and extent of LE after completion of therapy. The impact of these changes on neurocognitive functioning and quality of life in survivors remains to be determined.

Prevalence of leukoencephalopathy in children treated for acute lymphoblastic leukemia with high-dose methotrexate

BACKGROUND AND PURPOSE

An effective treatment for acute lymphoblastic leukemia (ALL), intravenous (IV) methotrexate (MTX) has a notable toxic effect on the CNS, with leukoencephalopathy (LE) being the most common form. The purpose of this study was to use objective quantitative MR imaging to prospectively assess potential risk factors on the temporal evolution of LE in patients treated for ALL.

METHODS

We evaluated the longitudinal prevalence of LE in 45 children treated for ALL in a single institutional protocol including seven courses of IV MTX and no cranial irradiation. Differences in signal intensity on T2-weighted and fluid-attenuated inversion recovery (FLAIR) images between hyperintense regions and normal-appearing genu were used to quantitatively detect LE. Cox proportional regression was used to estimate the effect of covariates (e.g., sex, MTX dose, age at diagnosis) on the prevalence of LE. After influential factors were identified, a generalized linear model was determined to predict the probability of LE in new patients. The model was necessary to facilitate statistical testing between examinations.

RESULTS

Increasing exposure, which corresponding to more courses and higher doses of IV MTX, influenced the prevalence of LE. The prevalence of LE was significant reduced approximately 1.5 years after the completion of IV MTX.

CONCLUSION

Higher doses and more courses of IV MTX placed patients at a higher risk for LE; many of the changes resolved after the completion of therapy. The effect of these changes on neurocognitive functioning and quality of life in survivors remains to be determined.

Atypical white matter volume development in children following craniospinal irradiation

Most children with medulloblastoma (MB), the second most common pediatric brain tumor, have a 70% probability of survival. However, survivors who receive aggressive therapy are at significant risk of cognitive deficits that have been associated with lower volumes of normal-appearing white matter (NAWM). We hypothesized that cranial irradiation inhibited normal brain volume development in these survivors. We retrospectively analyzed 324 MRI studies of 52 patients with histologically proven MB treated with surgery and 35 to 40 Gy craniospinal irradiation, with or without chemotherapy. The volume of NAWM and that of cerebrospinal fluid were quantified from a single index section and compared with those of healthy, age-similar control subjects. A quadratic random coefficient model was used to identify trends in brain volume with increasing age. Patients treated for MB at younger ages demonstrated substantially less development of NAWM volume than did their healthy peers. Younger age at the time of irradiation and the need for a ventricular shunt were significantly associated with reduced NAWM volume. NAWM and craniospinal fluid volume differences between patients who had shunts and those without resolved over a period of four to five years. NAWM volume is known to be associated with neurocognitive test performance, which shows deficiencies after cranial irradiation early in life. Therefore, volumetric monitoring of brain development can be used to guide the care of survivors, assess the toxicity of previous and current clinical trials, and aid in the design of therapies that minimize toxicity.

Improving the segmentation of therapy-induced leukoencephalopathy in children with acute lymphoblastic leukemia using a priori information and a gradient magnitude threshold

Reliably quantifying therapy-induced leukoencephalopathy is a challenging task due to the similarity between its MR properties and those of normal tissues. Multispectral MR images were analyzed for 15 children treated for acute lymphoblastic leukemia. Three different analysis techniques were compared to examine improvements in the segmentation accuracy of leukoencephalopathy versus manual tracings by two experienced observers. The original technique used a white matter mask based on the segmentation of the first serial examination of each patient and no a priori information. The modified techniques combine spatially normalized a priori maps as input and a gradient magnitude threshold. The second technique used a 2D threshold, while the third algorithm utilized a 3D threshold. MR images were segmented with a Kohonen self-organizing map for all three algorithms. Kappa values were compared for the three techniques to each observer and statistically significant improvements were seen between the original and third algorithms (Observer 1: 0.651, 0.744, P = 0.015; Observer 2: 0.603, 0.699, P = 0.024). More accurate and reliable quantification reduces the amount of variance in MR measures and facilitates clinical trials to determine the clinical significance of leukoencephalopathy in this vulnerable population.

Brain volume in pediatric patients with sickle cell disease: evidence of volumetric growth delay?

BACKGROUND AND PURPOSE

Despite the large body of data available about somatic growth delay in patients with sickle cell disease (SCD), virtually nothing is known about the effect of the disease on volumetric growth of the brain. This study was designed to test a hypothesis that children with SCD have a disease-related delay in brain volumetric growth compared with healthy children.

METHODS

A cross-sectional study design was used to evaluate 83 children with SCD and 43 age-similar healthy children, including 27 patient siblings. Brain volume was measured by segmenting and classifying MR imaging data, by using at least three separate image sets (T1-, T2-, and proton density-weighted MR images). A linear model was used to compare the various brain volumes with the covariates of group (patient versus control) and age, with age treated as a continuous variable.

RESULTS

With age controlled for, no significant difference was noted in total brain volume between patients and control subjects at age 9.5 years. However, patients showed a deficit specifically in gray matter volume (P=.005), without significant differences in white matter or ventricular volume. The deficit in patient gray matter was greater in central gray matter (P <.005) than in cortical gray matter (P <.02). In healthy control subjects, gray matter volume decreased significantly with age (P <.005), probably due to myelination of white matter tracts. In patients with SCD, gray matter volume did not change with age.

CONCLUSION

Volumetric growth of brain gray matter may be delayed in children with SCD, suggesting that there may be neurodevelopmental consequences of this disease.

Prediction of total cerebral tissue volumes in normal appearing brain from sub-sampled segmentation volumes

The need for anatomical coverage and multi-spectral information must be balanced against examination and processing time to ensure high-quality, feasible imaging protocols for clinical research of cerebral development in normal-appearing brains. The focus of this study was to create and assess models to estimate total cerebral volumes of gray matter, white matter, and cerebrospinal fluid (CSF) from anatomically defined sub-samples of full clinical examinations. Pediatric patients (18F, 11M; aged 1.7 to 18.7, median 5.2 years) underwent a clinical imaging protocol consisting of 3 mm contiguous T1-, T2-, PD-, and FLAIR-weighted images after obtaining informed consent. Magnetic resonance imaging (MRI) sets were registered, RF-corrected, and then analyzed with a hybrid neural network segmentation and classification algorithm to identify normal brain parenchyma. The correlation between the image subsets and the total cerebral volumes of gray matter, white matter and CSF were examined through linear regression analyses. Five sub-sampled sets were defined and assessed in each patient to produce estimation models which were all significantly correlated (p < 0.001) with the total cerebral volumes of gray matter, white matter, and CSF. Volumes were estimated from as little as a single representative slice requiring minimal processing time, 27 min, but with an average estimation error of approximately 6%. Larger sub-samples of approximately three-quarters of the full cerebral volume required much more processing time, 2 h and 4 min, but produced estimates with an average error less than 2%. This study demonstrated that investigators can choose the amount of cerebrum sampled to optimize the acquisition and processing time against the degree of accuracy needed in the total cerebral volume estimates.

Toxic leukoencephalopathy: a review and report of two chemotherapy-related cases

Leukoencephalopathy syndrome is a rare disorder that results from structural alterations of cerebral white matter, is characterized by cerebral edema, and can occur in patients of any age. Cranial irradiation and certain chemotherapy agents, especially those used in high-dose protocols, are causal agents. The prevalence of toxic leukoencephalopathy is unknown; however, this syndrome has been reported increasingly in the literature in patients who develop neurobehavioral changes following exposure to various toxins. Diagnosis must confirm exposure to a toxin and the presence of neurobehavioral deficits and neuroradiologic abnormalities. In most reported cases, clinical symptoms are reversible after the offending toxin is withdrawn. This article describes two cases of chemotherapy-related leukoencephalopathy and reviews the nursing care of patients experiencing this syndrome.

Prospective brain imaging evaluation of children with sickle cell trait: initial observations

PURPOSE

To determine whether sickle cell trait (hemoglobin AS) is associated with abnormalities in the brain of asymptomatic children.

MATERIALS AND METHODS

Magnetic resonance (MR) imaging and MR angiography were performed prospectively in 26 siblings (eight girls, 18 boys; mean age, 10.5 years) of patients with sickle cell disease. Two neuroradiologists, blinded as to whether a child had hemoglobin AS or AA, reviewed images obtained in siblings. With MR imaging, lacunae, loss of white matter volume, encephalomalacia, or leukoencephalopathy was identified. With MR angiography, arterial stenosis, occlusion, or tortuosity was identified. Images with definite or possible abnormalities were mixed with randomly selected images and were referred to a third neuroradiologist for a completely blinded review. In cases in which all neuroradiologists concurred, a score was assigned that indicated the sibling had an abnormality. MR angiographic findings were assigned a score for tortuosity with a new quantitative scale.

RESULTS

Among 26 siblings screened, 21 children had sickle cell trait. Among these 21 children, two had mild abnormalities at MR imaging (sample prevalence rate, 10% [95% CI: 1%, 29%]), and four had arterial tortuosity (sample prevalence rate, 19% [95% CI: 5%, 42%]). When children with sickle cell trait were compared with 31 control subjects without the trait, arterial tortuosity was significantly more common in children with sickle cell trait (P =.014). Among children with sickle cell trait, percentage of hemoglobin S was significantly greater in children who had tortuosity than percentage of hemoglobin S in children who had normal blood vessels at MR angiography (P <.03).

CONCLUSION

Findings suggest that greater percentage of hemoglobin S is associated with mild vasculopathy. This vasculopathy may explain some of the excess risk of stroke among African Americans.

Developmental model relating white matter volume to neurocognitive deficits in pediatric brain tumor survivors

BACKGROUND

The primary objective of this study was to test the hypothesis that, among survivors of pediatric brain tumors, the association between reduced volumes of normal-appearing white matter (NAWM) and intellectual/academic achievement deficits can be explained by patient problems with memory and attention.

METHODS

Quantitative tissue volumes from magnetic resonance imaging scans and neurocognitive assessments were obtained for 40 long-term survivors of pediatric brain tumors. They were treated with radiotherapy (RT) with or without chemotherapy 2.6-15.3 years earlier (median, 5.7 years) at an age of 1.7-14.8 years (median, 6.5 years). Neurocognitive assessments included standardized tests of intellect (intelligence quotient [IQ]), attention, memory, and academic achievement.

RESULTS

Analyses revealed significant impairments in patients' neurocognitive test performance on all measures. After statistically controlling for age at RT and time from RT, significant associations were found between NAWM volumes and both attentional abilities and IQ, and between attentional abilities and IQ. Subsequent analyses supported the hypothesis that attentional abilities, but not memory, could explain a significant amount of the relationship between NAWM and IQ. The final developmental model predicting academic achievement based on NAWM, attentional abilities, and IQ explained approximately 60% of the variance in reading and spelling and almost 80% of the variance in math.

CONCLUSIONS

The authors demonstrated that the primary consequence of reduced NAWM among pediatric patients treated for brain tumors was decreased attentional abilities, leading to declining IQ and academic achievement.

T2 relaxation time histograms in multiple sclerosis

An accurate measurement of the transverse relaxation time T(2), and the histogram of T(2) in the brain parenchyma can be accomplished in vivo using a multi-echo magnetic resonance imaging sequence. An estimate of the error in the T(2) measurement is derived using copper sulfate doped water phantoms. Correction factors are calculated and applied to the signal intensity of each voxel prior to the in vivo T(2) evaluation. These corrected T(2) are in good agreement with the theoretical values calculated from copper sulfate concentrations. This technique is then applied to calculate T(2) histograms of the brain. The population studied was composed of normal volunteers and multiple sclerosis patients. The corrected T(2) histogram method discriminates the normal control population from the MS population, and also discriminates between relapsing-remitting patients and primary progressive or secondary progressive patients. Moreover using this approach we are able to detect in MS patients a global shift of the T(2) of the white mater toward higher values. The results of this study showed that the method is easy to implement and may be used to characterize MS pathology.