Multiparameter MR imaging in the 6-OPRI variant of inherited prion disease.

BACKGROUND AND PURPOSE: Inherited prion diseases represent over 15% of human prion cases and are a frequent cause of early onset dementia. The purpose of this study was to define the distribution of changes in cerebral volumetric and microstructural parenchymal tissues in a specific inherited human prion disease mutation combining VBM with VBA of cerebral MTR and MD. MATERIALS AND METHODS: VBM and VBA of cerebral MTR and MD were performed in 16 healthy control participants and 9 patients with the 6-OPRI mutation. An analysis of covariance consisting of diagnostic grouping with age and total intracranial volume as covariates was performed. RESULTS: On VBM, there was a significant reduction in gray matter volume in patients compared with control participants in the basal ganglia, perisylvian cortex, lingual gyrus, and precuneus. Significant MTR reduction and MD increases were more anatomically extensive than volume differences on VBM in the same cortical areas, but MTR and MD changes were not seen in the basal ganglia. CONCLUSIONS: Gray matter and WM changes were seen in brain areas associated with motor and cognitive functions known to be impaired in patients with the 6-OPRI mutation. There were some differences in the anatomic distribution of MTR-VBA and MD-VBA changes compared with VBM, likely to reflect regional variations in the type and degree of the respective pathophysiologic substrates. Combined analysis of complementary multiparameter MR imaging data furthers our understanding of prion disease pathophysiology.

Tapping linked to function and structure in premanifest and symptomatic Huntington disease.

OBJECTIVE: Motor signs are functionally disabling features of Huntington disease. Characteristic motor signs define disease manifestation. Their severity and onset are assessed by the Total Motor Score of the Unified Huntington's Disease Rating Scale, a categorical scale limited by interrater variability and insensitivity in premanifest subjects. More objective, reliable, and precise measures are needed which permit clinical trials in premanifest populations. We hypothesized that motor deficits can be objectively quantified by force-transducer-based tapping and correlate with disease burden and brain atrophy. METHODS: A total of 123 controls, 120 premanifest, and 123 early symptomatic gene carriers performed a speeded and a metronome tapping task in the multicenter study TRACK-HD. Total Motor Score, CAG repeat length, and MRIs were obtained. The premanifest group was subdivided into A and B, based on the proximity to estimated disease onset, the manifest group into stages 1 and 2, according to their Total Functional Capacity scores. Analyses were performed centrally and blinded. RESULTS: Tapping variability distinguished between all groups and subgroups in both tasks and correlated with 1) disease burden, 2) clinical motor phenotype, 3) gray and white matter atrophy, and 4) cortical thinning. Speeded tapping was more sensitive to the detection of early changes. CONCLUSION: Tapping deficits are evident throughout manifest and premanifest stages. Deficits are more pronounced in later stages and correlate with clinical scores as well as regional brain atrophy, which implies a link between structure and function. The ability to track motor phenotype progression with force-transducer-based tapping measures will be tested prospectively in the TRACK-HD study.

Onset and progression of pathologic atrophy in Huntington disease: a longitudinal MR imaging study.

BACKGROUND AND PURPOSE: Longitudinal MR imaging measures provide an opportunity to track progression in HD before the emergence of clinical symptoms. This may prove useful in assessing disease-modifying treatments. We investigated how caudate and global volumes change as HD progresses from premanifest to early disease. MATERIALS AND METHODS: Forty HD gene-positive individuals and 19 controls underwent serial volumetric MR imaging (baseline, 12 and 27 months; 2 or 3 scans per person). At baseline, 3 patients with HD were premanifest but developed overt motor features during the study, and 37 had early HD. All had dates of motor onset recorded. Caudates, lateral ventricles, and TIVs were measured using semiautomated procedures. Linear mixed models were used to investigate differences between HD and controls in relation to motor onset, controlling for TIV, sex, and age. RESULTS: Extrapolating backwards in time, we found that differences in caudate and ventricular volumes between patients with HD and controls were evident 14 and 5 years, respectively, before motor onset (P < .05). At onset, caudate volume was 2.58 mL smaller than that in controls (P < .0001); ventricular volume was 9.27 mL larger (P < .0001). HD caudate atrophy rates were linear, showed low variability between subjects, and were approximately 10-fold higher than those in controls (P < .001). HD ventricular enlargement rates were variable between subjects, were approximately 4-fold higher than those in controls at onset (P < .001), and accelerated with disease duration (P = .02). CONCLUSIONS: We provide evidence of acceleration of global atrophy in HD with disproportionate caudate involvement. Both caudate and global measures may be of use as early markers of HD pathology.

Pitfalls in the use of voxel-based morphometry as a biomarker: examples from huntington disease.

BACKGROUND AND PURPOSE: VBM is increasingly used in the study of neurodegeneration, and recently there has been interest in its potential as a biomarker. However, although it is largely "automated," VBM is rarely implemented consistently across studies, and changing user-specified options can alter the results in a way similar to the very biologic differences under investigation. MATERIALS AND METHODS: This work uses data from patients with HD to demonstrate the effects of several user-specified VBM parameters and analyses: type and level of statistical correction, modulation, smoothing kernel size, adjustment for brain size, subgroup analysis, and software version. RESULTS: The results demonstrate that changing these options can alter results in a way similar to the biologic differences under investigation. CONCLUSIONS: If VBM is to be useful clinically or considered for use as a biomarker, there is a need for greater recognition of these issues and more uniformity in its application for the method to be both reproducible and valid.

A comparison of methods for the automated calculation of volumes and atrophy rates in the hippocampus.

Hippocampal atrophy rates have been used in a number of studies in Alzheimer's disease (AD) to assess disease progression and are being increasingly utilized as an outcome measure in clinical trials of new pharmaceutical agents. Owing to the labor-intensive nature of hippocampal segmentation, more automated approaches are required for such analysis. In this study we compared methods of automatically segmenting the hippocampus (single-person template and template library) on the baseline image in a group of probable AD (n=36) and control (n=19) subjects with serial images. Using the method that gave most similar results to manual, three automated methods of calculating change within the hippocampal region were compared: fluid change calculated using (1) Jacobian change or (2) region propagation and (3) boundary shift. Rates were compared with manual measures. We found that segmentation of baseline hippocampus was most accurate using a template library combined with morphological operations (intensity thresholding plus one conditional dilation). This gave a voxel similarity of 0.69 (0.05) and 0.72 (0.06) in controls and probable AD subjects respectively compared with manual measures. Atrophy rates within these regions were most similar to the manual rates using the boundary shift integral (mean difference from manual rate 0.03% (1.29) in controls and 0.48% (2.44) in AD). A template library segmentation approach, together with morphological operations, provides a segmentation accurate enough to quantify relative change over time. The change over time can then be calculated automatically using boundary shift or fluid measures, with boundary shift giving most similar results to manual.

Increased hippocampal atrophy rates in AD over 6 months using serial MR imaging.

We measured hippocampi on baseline-, 6- and 12-month scans in a group of AD (n=36) and control subjects (n=20). We found that mean annualised atrophy rates using 6-month intervals were comparable at a group level to those generated from a 12-month interval. Higher variance was seen using shorter intervals, although this was only significant in the control group. This has implications where shorter inter-scan intervals may be advantageous, such as rapid diagnosis, and tracking of disease progression including in a clinical trial.

Automatic calculation of hippocampal atrophy rates using a hippocampal template and the boundary shift integral.

We describe a method of automatically calculating hippocampal atrophy rates on T1-weighted MR images without manual delineation of hippocampi. This method was applied to a group of Alzheimer's disease (AD) (n=36) and control (n=19) subjects and compared with manual methods (manual segmentation of baseline and repeat-image hippocampi) and semi-automated methods (manual segmentation of baseline hippocampi only). In controls, mean (S.D.) atrophy rates for manual, semi-automated, and automated methods were 18.1 (53.5), 15.3 (50.2) and 11.3 (50.4) mm3 loss per year, respectively. In AD patients these rates were 174.6 (106.5) 159.4 (101.2) and 172.1 (123.1) mm3 loss per year, respectively. The automated method was a significant predictor of disease (p=0.001) and gave similar group discrimination compared with both semi-automated and manual methods. The automated hippocampal analysis in this small study took approximately 20 min per hippocampal pair on a 3.4 GHz Intel Xeon server, whereas manual delineation of each hippocampal pair took approximately 90 min of operator-intensive labour. This method may be useful diagnostically or in studies where analysis of many scans may be required.

Improved reliability of hippocampal atrophy rate measurement in mild cognitive impairment using fluid registration.

MRI-derived rates of hippocampal atrophy may serve as surrogate markers of disease progression in mild cognitive impairment (MCI). Manual delineation is the gold standard in hippocampal volumetry; however, this technique is time-consuming and subject to errors. We aimed to compare regional non-linear (fluid) registration measurement of hippocampal atrophy rates against manual delineation in MCI. Hippocampi of 18 subjects were manually outlined twice on MRI scan-pairs (interval+/-SD: 2.01+/-0.11 years), and volumes were subtracted to calculate change over time. Following global affine and local rigid registration, regional fluid registration was performed from which atrophy rates were derived from the Jacobian determinants over the hippocampal region. Atrophy rates as derived by fluid registration were computed using both forward (repeat onto baseline) and backward (baseline onto repeat) registration. Reliability for both methods and agreement between methods was assessed. Mean+/-SD hippocampal atrophy rates (%/year) derived by manual delineation were: left: 2.13+/-1.62; right: 2.36+/-1.78 and for regional fluid registration: forward: left: 2.39+/-1.68; right: 2.49+/-1.52 and backward: left: 2.21+/-1.51; right: 2.42+/-1.49. Mean hippocampal atrophy rates did not differ between both methods. Reliability for manual hippocampal volume measurements (cross-sectional) was high (intraclass correlation coefficient (ICC): baseline and follow-up, left and right, >0.99). However, the resulting ICC for manual measurements of hippocampal volume change (longitudinal) was considerably lower (left: 0.798; right: 0.850) compared with regional fluid registration (forward: left: 0.985; right: 0.988 and backward: left: 0.975; right: 0.989). We conclude that regional fluid registration is more reliable than manual delineation in assessing hippocampal atrophy rates, without sacrificing sensitivity to change. This method may be useful to quantify hippocampal volume change, given the reduction in operator time and improved precision.

Longitudinal imaging in dementia.

Dementia represents one of the major public health problems facing ageing populations, with 20% of those over 80 years of age suffering from this disorder. The advent of therapeutic agents has brought about an increasing demand for a more accurate and earlier diagnosis, and the value of neuroimaging in improving the diagnostic process is becoming widely accepted. Neuroimaging assessments may add weight to a diagnosis of neurodegeneration as opposed to healthy ageing, improve the differential diagnosis, aid in the prediction of conversion to dementia in individuals at a higher risk of developing the disorder, track disease progression and provide an outcome measure for assessment of drug efficacy.

Mapping the onset and progression of atrophy in familial frontotemporal lobar degeneration.

BACKGROUND: Frontotemporal lobar degeneration (FTLD) may be inherited as an autosomal dominant disease. Studying patients "at risk" for developing FTLD can provide insights into the earliest onset and evolution of the disease. METHOD: We carried out approximately annual clinical, MRI, and neuropsychological assessments on an asymptomatic 51 year old "at risk" family member from a family with FTLD associated with ubiquitin-positive and tau-negative inclusion bodies. We used non-linear (fluid) registration of serial MRI to determine areas undergoing significant regional atrophy at different stages of the disease. RESULTS: Over the first 26 months of the study, the patient remained asymptomatic, but subsequently developed progressive speech production difficulties, and latterly severe orofacial dyspraxia, dyscalculia, frontal executive impairment, and limb dyspraxia. Regional atrophy was present prior to the onset of symptoms, and was initially centred on the left dorsolateral prefrontal cortex and the left middle frontal gyrus. Latterly, there was increasing asymmetric left frontal and parietal atrophy. Imaging revealed excess and increasing global atrophy throughout the study. Neuropsychological evaluation revealed mild intellectual impairment prior to the onset of these clinical symptoms; frontal executive and left parietal impairment subsequently emerged, culminating in widespread cognitive impairment. Fluid registered MRI allowed the emerging atrophy patterns to be delineated. CONCLUSION: We have demonstrated the onset and progressive pattern of in vivo atrophy in familial FTLD using fluid registered MRI and correlated this with the clinical features. Fluid registered MRI may be a useful technique in assessing patterns of focal atrophy in vivo and demonstrating the progression of degenerative diseases.

Epilepsy presenting as AD: neuroimaging, electroclinical features, and response to treatment.

Three patients with progressive memory impairment initially attributed to AD underwent serial neuropsychometry, MRI, and EEG. Registered serial MRI volumetric analysis showed no loss of whole or regional brain volume. EEG revealed temporal lobe spike activity and antiepileptic treatment was optimized. Memory functions improved with antiepileptic medication in all three patients. The demonstration of temporal lobe spike activity in patients with progressive memory impairment is an indication for a trial of antiepileptic medication.

Rates of global and regional cerebral atrophy in AD and frontotemporal dementia.

OBJECTIVE: Serial registered MRI provides a reproducible technique for detecting progressive cerebral atrophy in vivo and was used to determine if there were differences between the rates of cerebral atrophy in AD and frontotemporal dementia (FTD). METHODS: Eighty-four patients with dementia (54 AD and 30 FTD) and 27 age-matched control subjects each had at least two volumetric MR scans. Serial scans were positionally matched (registered), and brain volume loss was determined by calculation of the brain boundary shift integral. RESULTS: There was a difference between the rates of whole-brain atrophy in patients (mean annual volume loss 2.7% of total brain volume) and in control subjects (mean annual volume loss 0.5%). AD and FTD were associated with different rates of atrophy (mean annual losses 2.4 and 3.2%). The range of atrophy rates in the FTD group (0.3 to 8.0%) greatly exceeded that in the AD group (0.5 to 4.7%). Frontal-variant FTD was associated with a wider range of atrophy rates than temporal-variant FTD. Analysis of regional brain atrophy rates revealed that there was widespread symmetrically distributed cerebral volume loss in AD, whereas in frontal FTD there was greater atrophy anteriorly and in temporal FTD the atrophy rate was greatest in the left anterior cerebral cortex. CONCLUSIONS: Both AD and FTD patients had increased rates of brain atrophy. Whereas the patients with AD were associated with a relatively restricted spread of atrophy rates, the greater spread of rates observed in the patients with FTD may reflect the heterogeneity of disease in FTD, with differences observed between frontal and temporal FTD. Increased rates of whole-brain atrophy did not discriminate AD from FTD, but analysis of regional atrophy rates revealed marked differences between patient groups.

Imaging of onset and progression of Alzheimer's disease with voxel-compression mapping of serial magnetic resonance images.

BACKGROUND: Early diagnosis and monitoring of the progression of Alzheimer's disease is important for the development of therapeutic strategies. To detect the earliest structural brain changes, individuals need to be studied before symptom onset. We used an imaging technique known as voxel-compression mapping to localise progressive atrophy in patients with preclinical Alzheimer's disease. METHODS: Four symptom-free individuals from families with early-onset Alzheimer's disease with known autosomal dominant mutations underwent serial magnetic resonance imaging (MRI) over 5-8 years. All four became symptomatic during follow-up. 20 individuals with a clinical diagnosis of probable Alzheimer's disease and 20 control participants also underwent serial MR imaging. A non-linear fluid matching algorithm was applied to register repeat scans onto baseline imaging. Jacobian determinants were used to create the voxel-compression maps. FINDINGS: Progressive atrophy was revealed in presymptomatic individuals, with posterior cingulate and neocortical temporoparietal cortical losses, and medial temporal-lobe atrophy. In patients with known Alzheimer's disease, atrophy was widespread apart from in the primary motor and sensory cortices and cerebellum, reflecting the clinical phenomenology. INTERPRETATION: Voxel-compression maps confirmed early involvement of the medial temporal lobes, but also showed posterior cingulate and temporoparietal cortical losses at presymptomatic stage. This technique could be applied diagnostically and used to monitor the effects of therapeutic intervention.

Patterns of temporal lobe atrophy in semantic dementia and Alzheimer's disease.

Volumetric magnetic resonance imaging analyses of 30 subjects were undertaken to quantify the global and temporal lobe atrophy in semantic dementia and Alzheimer's disease. Three groups of 10 subjects were studied: semantic dementia patients, Alzheimer's disease patients, and control subjects. The temporal lobe structures measured were the amygdala, hippocampus, entorhinal cortex, parahippocampal gyrus, fusiform gyrus, and superior, middle, and inferior temporal gyri. Semantic dementia and Alzheimer's disease groups did not differ significantly on global atrophy measures. In semantic dementia, there was asymmetrical temporal lobe atrophy, with greater left-sided damage. There was an anteroposterior gradient in the distribution of temporal lobe atrophy, with more marked atrophy anteriorly. All left anterior temporal lobe structures were affected in semantic dementia, with the entorhinal cortex, amygdala, middle and inferior temporal gyri, and fusiform gyrus the most severely damaged. Asymmetrical, predominantly anterior hippocampal atrophy was also present. In Alzheimer's disease, there was symmetrical atrophy of the entorhinal cortex, hippocampus, and amygdala, with no evidence of an anteroposterior gradient in the distribution of temporal lobe or hippocampal atrophy. These data demonstrate that there is a marked difference in the distribution of temporal lobe atrophy in semantic dementia and Alzheimer's disease. In addition, the pattern of atrophy in semantic dementia suggests that semantic memory is subserved by anterior temporal lobe structures, within which the middle and inferior temporal gyri may play a key role.

Automated hippocampal segmentation by regional fluid registration of serial MRI: validation and application in Alzheimer's disease.

The application of voxel-level three-dimensional registration to serial magnetic resonance imaging (MRI) is described. This fluid registration determines deformation fields modeling brain change, which are consistent with a model describing a viscous fluid. The objective was to validate the measurement of hippocampal volumetric change by fluid registration in Alzheimer's disease (AD) against current methodologies. The hippocampus was chosen for this study because it is difficult to measure reproducibly by manual segmentation and is widely studied; however, the technique is applicable to any structure which can be delineated on a scan. First, suitable values for the viscosity-body-force-ratio, alpha (0.01), and the number of iterations (300), were established and the convergence, repeatability, linearity, and accuracy investigated and compared with expert manual segmentation. A simple model of hippocampal atrophy was used to compare simulated volumetric change against that obtained by fluid registration. Finally the serial segmentation was compared with the current gold standard technique-expert human labeling with a volume repeatability of approximately 4%-in 27 subjects (15 normal controls, 12 clinically diagnosed with Alzheimer's disease). The scan-rescan volumetric consistency of serial segmentation by fluid-registration was shown to be superior to human serial segmentors ( approximately 2%). The mean absolute volume difference between fluid and manual segmentation was 0.7%. Fluid registration has potential importance for tracking longitudinal structural changes in brain particularly in the context of the clinical trial where large numbers of subjects may have multiple MR scans.

Correlation between rates of brain atrophy and cognitive decline in AD.

Twenty-nine untreated patients diagnosed with probable AD and 15 control patients underwent two or more clinical and volumetric MRI assessments with intervals ranging from 5 months to 6 years. The change in global cerebral volume for an individual was calculated by a novel method of registration and subtraction of serial scans. Rate of global cerebral volume loss correlated strongly with rate of change in Mini-Mental State Examination scores (r = 0.80, p < 0.001), implying clinical relevance to this marker of progression.