A full-brain, bootstrapped analysis of diffusion tensor imaging robustly differentiates Parkinson disease from healthy controls

There is a compelling need for early, accurate diagnosis of Parkinson's disease (PD). Various magnetic resonance imaging modalities are being explored as an adjunct to diagnosis. A significant challenge in using MR imaging for diagnosis is developing appropriate algorithms for extracting diagnostically relevant information from brain images. In previous work, we have demonstrated that individual subject variability can have a substantial effect on identifying and determining the borders of regions of analysis, and that this variability may impact on prediction accuracy. In this paper we evaluate a new statistical algorithm to determine if we can improve accuracy of prediction using a subjects left-out validation of a DTI analysis. Twenty subjects with PD and 22 healthy controls were imaged to evaluate if a full brain diffusion tensor imaging-fractional anisotropy (DTI-FA) map might be capable of segregating PD from controls. In this paper, we present a new statistical algorithm based on bootstrapping. We compare the capacity of this algorithm to classify the identity of subjects left out of the analysis with the accuracy of other statistical techniques, including standard cluster-thresholding. The bootstrapped analysis approach was able to correctly discriminate the 20 subjects with PD from the 22 healthy controls (area under the receiver operator curve or AUROC 0.90); however the sensitivity and specificity of standard cluster-thresholding techniques at various voxel-specific thresholds were less effective (AUROC 0.72-0.75). Based on these results sufficient information to generate diagnostically relevant statistical maps may already be collected by current MRI scanners. We present one statistical technique that might be used to extract diagnostically relevant information from a full brain analysis.

Accurate localization of brain activity in presurgical FMRI by structure adaptive smoothing

An important problem of the analysis of functional magnetic resonance imaging (fMRI) experiments is to achieve some noise reduction of the data without blurring the shape of the activation areas. As a novel solution to this problem, recently the propagation-separation (PS) approach has been proposed. PS is a structure adaptive smoothing method that adapts to different shapes of activation areas. In this paper, we demonstrate how this method results in a more accurate localization of brain activity. First, it is shown in numerical simulations that PS is superior over Gaussian smoothing with respect to the accurate description of the shape of activation clusters and results in less false detections. Second, in a study of 37 presurgical planning cases we found that PS and Gaussian smoothing often yield different results, and we present examples showing aspects of the superiority of PS as applied to presurgical planning.

Quantitative objective markers for upper and lower motor neuron dysfunction in ALS

OBJECTIVE

To investigate the value of objective biomarkers for upper (UMN) and lower (LMN) motor neuron involvement in ALS.

METHODS

We prospectively studied 64 patients with ALS and its subsets using clinical measures, proton MR spectroscopic imaging ((1)H MRSI), diffusion tensor imaging, transcranial magnetic stimulation, and the motor unit number estimation (MUNE) at baseline and every 3 months for 15 months and compared them with control subjects.

RESULTS

(1)H MRSI measures of the primary motor cortex N-acetyl-aspartate (NAA) concentration were markedly reduced in ALS (p = 0.009) and all UMN syndromes combined (ALS, familial ALS [fALS], and primary lateral sclerosis; p = 0.03) vs control values. Central motor conduction time to the tibialis anterior was prolonged in ALS (p < 0.0005) and combined UMN syndromes (p = 0.001). MUNE was lower in ALS (p < 0.0005) and all LMN syndromes combined (ALS, fALS, and progressive muscular atrophy; p = 0.001) vs controls. All objective markers correlated well with the ALS Functional Rating Scale-Revised, finger and foot tapping, and strength testing, suggesting these markers related to disease activity. Regarding changes over time, MUNE changed rapidly, whereas neuroimaging markers changed more slowly and did not significantly differ from baseline.

CONCLUSIONS

(1)H MR spectroscopic imaging measures of the primary motor cortex N-acetyl-aspartate (NAA) concentration and ratio of NAA to creatine, central motor conduction time to the tibialis anterior, and motor unit number estimation significantly differed between ALS, its subsets, and control subjects, suggesting they have potential to provide insight into the pathobiology of these disorders.

Diffusion anisotropy changes in the brains of professional boxers

BACKGROUND AND PURPOSE

Professional boxing may result in brain injury. We hypothesize that quantitative MR diffusion imaging may be useful in determining early white matter changes.

METHODS

Forty-nine professional boxers (age 30 +/- 4.5 years) and 19 healthy control subjects (age 32 +/- 9.5 years) were imaged on a clinical 1.5T scanner. None of the subjects had neurologic disorder or deficit. The average diffusion constant (D(av)) and diffusion anisotropy (FA) were determined pixel by pixel. Regional diffusion measurements were done in the corpus callosum (CC) and internal capsule (IC). The whole brain diffusion constant (BD(av)) was also determined. Student t test was used to analyze the diffusion difference between boxers and the healthy control subjects. P < .05 was considered statistically significant.

RESULTS

Of the 49 professional boxers, 42 had normal conventional MRIs. The remaining 7 boxers had abnormal MR imaging findings dominated by nonspecific white matter disease. There was a significant difference in diffusion and anisotropy measurements in all the boxers compared with the healthy control subjects. In the boxer group, BD(av) increased and FA decreased significantly in the CC and posterior limb of IC. The measured FA and D(av) inversely correlated in regions of CC and IC in boxers but not in healthy control subjects. BD(av) also robustly correlated with both FA and D(av) in the splenium of CC in boxers.

CONCLUSION

Increased BD(av) and the decreased FA in the CC and IC may represent preclinical signs of subtle brain injury in professional boxers.

Creatine in Huntington disease is safe, tolerable, bioavailable in brain and reduces serum 8OH2'dG

In a randomized, double-blind, placebo-controlled study in 64 subjects with Huntington disease (HD), 8 g/day of creatine administered for 16 weeks was well tolerated and safe. Serum and brain creatine concentrations increased in the creatine-treated group and returned to baseline after washout. Serum 8-hydroxy-2'-deoxyguanosine (8OH2'dG) levels, an indicator of oxidative injury to DNA, were markedly elevated in HD and reduced by creatine treatment.

Parametric manipulation of conflict and response competition using rapid mixed-trial event-related fMRI

In the current study we examined the influence of preceding context on attentional conflict and response competition using a flanker paradigm. Nine healthy right-handed adults participated in a rapid mixed trial event-related functional magnetic resonance imaging (fMRI) study, in which increasing numbers of either compatible or incompatible trials preceded an incompatible trial. Behaviorally, reaction times on incompatible trials increased as a function of the number of preceding compatible trials. Several brain regions showed monotonic changes to the preceding context manipulation. The most common pattern was observed in anterior cingulate, dorsolateral prefrontal, and superior parietal regions. These areas showed an increase in activity for incompatible trials as the number of preceding compatible trials increased and a decrease in activity for incompatible trials as the number of preceding incompatible trials increased. Post hoc analysis showed that while the MR signal in the anterior cingulate and dorsolateral prefrontal regions peaked before the superior parietal region, the dorsolateral prefrontal MR signal peaked early and remained at this level. These findings are consistent with the conflict monitoring theory that postulates that the anterior cingulate cortex detects or monitors conflict, while PFC is involved in control adjustments that may then lead to modulation of superior parietal cortex in top-down biasing of attention.

Elevated CNS average diffusion constant in Fabry disease

AIMS

Evaluation of the average brain diffusion constant in Fabry disease.

INTRODUCTION

Fabry disease is an X-linked recessive lysosomal storage disorder secondary to deficiency of alpha-galactosidase A and resulting in excess tissue globotriaosylceramide, particularly in cerebral blood vessels. This has been associated with cerebral hyperperfusion. Increased tissue perfusion should increase interstitial water by the Starling relationship. This hypothesis was examined by measuring the average CNS diffusion constant (Dav) in patients with Fabry disease using diffusion-weighted magnetic resonance imaging (DWI).

METHODS

Axial DWI was performed at b=0 seconds/mm2 and b = 1000 seconds/mm2 (TR (pulse repetition time), 10000; TE (time to echo), 100; FOV (field of view), 22 cm: 3 mm interleaved slices; image matrix, 128 x 128; GE Signa, 1.5T). Eight healthy male volunteers (age range, 21-47 years) and 17 hemizygous patients with Fabry disease (age range, 19-49 years) were examined. Following DWI acquisition, the trace image and the diffusion distribution map were calculated. The diffusion distribution curve was then fitted by a multi-modal Gaussian curve, allowing estimation of Dav.

RESULTS

The Dav was 0.743 +/- 0.024 x 10(-5) cm2/second (mean +/- SD) for patients with Fabry disease and 0.726 +/- 0.014 x 10(-5) cm2/second for the control group. Dav was significantly increased in the patients with Fabry disease compared with the controls (p = 0.029)

CONCLUSIONS

The elevated Dav indicates increased brain tissue water diffusivity in patients with Fabry disease, a finding consistent with increased extracellular water and increased cerebral blood flow.

Proton MR spectroscopic imaging predicts lesion progression on MRI in X-linked adrenoleukodystrophy

BACKGROUND

The phenotypic expression of X-linked adrenoleukodystrophy (X-ALD) ranges from the rapidly progressive childhood cerebral form to the milder adrenomyeloneuropathy in adults. It is not possible to predict phenotype by mutation analysis or biochemical assays. Multislice proton MRS imaging (MRSI) has previously detected more extensive brain abnormalities in X-ALD than conventional MRI, which has been suggested to predict impending demyelination. However, the significance of these changes is unclear.

OBJECTIVE

The purpose of this study was to determine the long-term sensitivity and specificity of MRSI for disease progression in X-ALD.

METHODS

Twenty-five patients with X-ALD were investigated (average age, 15 years; range, 2-43 years) with MRI and proton MRSI at baseline and follow-up MRI over a mean period of 3.5 years. Eight patients had normal MRI findings at baseline and on follow-up (noncerebral group), 11 had abnormal MRI at baseline and no change on follow-up (cerebral nonprogressive group), and 6 had progressive MRI abnormalities (cerebral progressive group). On MRSI, voxels were analyzed in the normal MRI-appearing perilesional white matter, or in the corresponding area in the noncerebral group.

RESULTS

The concentration ratio of N-acetylaspartate (NAA) to choline was the most sensitive indicator of disease progression. The average NAA/choline ratio was 5.99 for the noncerebral group, 5.75 for the cerebral nonprogressive group, and 3.74 for the cerebral progressive group (p = 0.002). At a cut-off point of 5.0, the NAA/choline ratio predicted disease progression in all patients with six cerebral progressive disease (sensitivity 100%). The specificity was 83%, the positive predictive value was 66%, and the negative predictive value was 100%.

CONCLUSIONS

Multislice proton MRS imaging is able to identify impending or beginning degeneration in white matter that still appears normal on conventional MRI. Multislice proton MRSI may be a suitable technique for the prediction of lesion progression on MRI in X-linked adrenoleukodystrophy.

Proton magnetic resonance spectroscopy of choroid plexus tumors in children

A variety of lesions may present as intraventricular masses in children. We report quantitative proton magnetic resonance spectroscopy (MRS) of two intraventricular tumors of the choroid plexus: choroid plexus carcinoma (CPC) and choroid plexus papilloma (CPP). Both lesions were characterized by high levels of choline-containing compounds and a complete absence of creatine and the neuronal/axonal marker N-acetyl aspartate. The CPC showed higher levels of choline compared to the CPP, and it also had elevated lactate. These preliminary results, if confirmed in a larger cohort of patients, indicate that proton MRS may have a role in the presurgical diagnosis of choroid plexus tumors in children, which may also have important implications for therapy and prognosis.

Hyperintense signal abnormality in subarachnoid spaces and basal cisterns on MR images of children anesthetized with propofol: new fluid-attenuated inversion recovery finding

BACKGROUND AND PURPOSE

MR imaging is the method of choice for pediatric neuroimaging. Sedation is often needed to suppress patient motion and ensure diagnostic image quality, and propofol is rapidly becoming the preferred anesthetic. The purpose of this study was to document a new finding on fast fluid-attenuated inversion recovery (fast-FLAIR) MR images of children anesthetized with propofol that can be mistaken for subarachnoid space pathologic abnormality.

METHODS

A retrospective analysis was conducted of 55 MR images of the brain for children who ranged in age from 1 week to 12 years. Forty-two patients received chloral hydrate, and 13 received propofol anesthetic. Multiplanar MR images were studied to detect the presence or absence of hyperintense signal (artifact) in the subarachnoid spaces and basal cisterns. The T1 values and null times of chloral hydrate, propofol, and CSF were determined in vitro at room temperature by using an inversion recovery pulse sequence at 1.5 T.

RESULTS

The fast-FLAIR images of all 13 patients who received propofol had hyperintense signal abnormality. For 10 (77%) of 13 patients, this artifact was in the basal cisterns and subarachnoid spaces overlying the brain convexity. For three (23%) of 13 patients, this artifact was in the convexity region only. Two patients underwent follow-up MR imaging with a nonpropofol anesthetic agent, and the artifact resolved. None of the images of the children who received chloral hydrate had this artifact. The T1 value of chloral hydrate was 0.2 s, of propofol was 1.86 s, and of CSF was 2.32 s at room temperature.

CONCLUSION

The fast-FLAIR images of children anesthetized with propofol have artifactual hyperintense signal in the basal cisterns and subarachnoid spaces, and this artifact mimics disease of the subarachnoid space. The T1 value of propofol approaches that of CSF. Depending on the chosen null time, there may be incomplete nulling of signal coming from propofol. To account for this observation, other possible causes include increased CSF pulsation in children creating motion artifact, changes in arterial oxygen concentration intrinsic to propofol or related to the supplemental oxygen normally administered, or changes in CSF protein levels related to propofol binding to proteins for uptake into CSF.

Diffusion tensor imaging of patients with HIV and normal-appearing white matter on MR images of the brain

BACKGROUND AND PURPOSE

HIV enters the CNS early in the course of infection and produces neuropsychiatric impairment throughout the course of illness, which preferentially affects the subcortical white matter. The development of a neuroimaging marker of HIV may allow for the earliest detection of cognitive impairment. The purpose of this study was to determine whether MR diffusion tensor imaging can detect white matter abnormalities in patients who have tested positive for HIV.

METHODS

Ten patients with HIV (eight men and two women; mean age, 42 years) underwent MR imaging of the brain with MR diffusion tensor imaging, which included routine fluid-attenuated inversion recovery and fast spin-echo T2-weighted imaging. Diffusion constants and anisotropy indices were calculated from diffusion tensor maps. Peripheral viral load, Centers for Disease Control staging, and cluster of differentiation 4 levels were determined.

RESULTS

All patients had normal results of MR imaging of the brain, except for mild atrophy. Four of 10 patients had undetectable viral loads. These patients were receiving highly active antiretroviral therapy. The diffusion constant and anisotropy were normal. Four of 10 patients had viral loads between 10,000 and 200,000. Diffusion anisotropy in the splenium and genu was significantly decreased (P < .02). The diffusion constant of the subcortical white matter was elevated in the frontal and parietooccipital lobes (11%). Two of 10 patients had viral loads >400,000. Anisotropy of the splenium was half normal (P < .0004) and of the genu was decreased 25% (P < .002). The average diffusion constant was diffusely elevated in the subcortical white matter.

CONCLUSION

Calculating the diffusion constant and anisotropy in the subcortical white matter and corpus callosum in patients with HIV detected abnormalities despite normal-appearing white matter on MR images and nonfocal neurologic examinations. Patients with the highest diffusion constant elevations and largest anisotropy decreases had the most advanced HIV disease. Patients with the lowest viral load levels, who had normal anisotropy and diffusion constants, were receiving highly active antiretroviral therapy.

MR diffusion imaging in stroke: review and controversies

Magnetic resonance (MR) diffusion imaging allows detection of cerebral ischemia within minutes of onset, and the temporal evolution of diffusion characteristics enables differentiation of acute from chronic stroke. T2-weighted MR imaging demonstrates infarcted tissue but fails to demonstrate acutely ischemic regions. Furthermore, the similar signal intensity characteristics of acute and chronic stroke on T2-weighted images limit the ability to determine the acuteness of an infarct. Diffusion imaging thus has tremendous potential for helping direct the treatment of acute ischemic stroke. Controversy exists over the pathophysiology of underlying changes in diffusion and the reversibility of changes after reperfusion in humans. There is also a lack of reproducibility in the time course of diffusion changes between research centers. Use of optimal diffusion imaging strategies results in increased conspicuity of ischemic regions and increased reproducibility of diffusion constants between research centers. An understanding of the principles of diffusion imaging and current controversies in the field is necessary for optimal application of this technique in the evaluation and treatment of cerebral ischemia.

Improved tissue characterization in adrenoleukodystrophy using magnetization transfer imaging

OBJECTIVE

We performed this study to evaluate the usefulness of magnetization transfer (MT) imaging techniques and magnetization transfer ratio (MTR) measurements in assessing patients with adrenoleukodystrophy (ALD).

SUBJECTS AND METHODS

Twelve patients who encompassed the range of ALD phenotypes were evaluated prospectively with MR and MT imaging (including digital subtraction images). The MT images and spin-echo MR images were compared by two staff neuroradiologists and a staff neurologist for extent of disease, different zones of involvement, and the presence of enhancement. MTR measurements were obtained from affected and unaffected regions of the brain.

RESULTS

Eight of the 12 patients exhibited gadolinium enhancement. In seven of these patients, the MT subtraction images showed two zones of abnormal signal within the affected white matter. Their MTR measurements were classified as zone 1 (mean MTR, 35%; SD, 6%) and zone 2 (mean MTR, 20%; SD, 6%). Three of the other patients showed a single zone of involvement corresponding to the affected white matter on the standard spin-echo MR images. Their MTR measurements were similar to that of zone 1. The remaining two patients had no demonstrable signal abnormalities on any of the images. We noted no difference in any of the 12 subjects in the extent of white matter involvement on any of the imaging techniques. The MTR measurements in the unaffected white matter (mean MTR, 46%; SD, 5%) approximated established MTRs in white matter of normal volunteers.

CONCLUSION

MT imaging and MTR measurements are helpful clinical techniques that may improve the evaluation of patients with ALD, particularly in the proposed ability of these techniques to divide the affected white matter into different zones that correspond to specific pathologic areas. These techniques can help the understanding of pathogenetic mechanisms and the evaluation of therapies.