Jonathan J. Wisco

Spatial clustering of hemorrhages in probable cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) is a common cause of symptomatic intracerebral hemorrhage (ICH), as well as small asymptomatic hemorrhage in the elderly. We used gradient‐echo MRI to analyze spatial distribution of 321 hemorrhages in 59 patients with probable CAA–related ICH. Hemorrhagic lesions were found preferentially in the temporal (ratio of actual to expected hemorrhages = 1.37) and occipital lobes (ratio = 1.45, p < 0.0001). Within individuals, hemorrhages tended to cluster, regardless of lobe (p < 0.0001). Among subjects followed prospectively for recurrence, clustering of new symptomatic and asymptomatic hemorrhages was observed. These data suggest that regional differences within the brain play a role in the development of CAA–related hemorrhage. Ann Neurol 2005;58:459–462

Using the wild bootstrap to quantify uncertainty in diffusion tensor imaging

Estimation of noise‐induced variability in diffusion tensor imaging (DTI) is needed to objectively follow disease progression in therapeutic monitoring and to provide consistent readouts of pathophysiology. The noise variability of nonlinear quantities of the diffusion tensor (e.g., fractional anisotropy, fiber orientation, etc.) have been quantified using the bootstrap, in which the data are resampled from the experimental averages, yet this approach is only applicable to DTI scans that contain multiple averages from the same sampling direction. It has been shown that DTI acquisitions with a modest to large number of directions, in which each direction is only sampled once, outperform the multiple averages approach. These acquisitions resist the traditional (regular) bootstrap analysis though. In contrast to the regular bootstrap, the wild bootstrap method can be applied to such protocols in which there is only one observation per direction. Here, we compare and contrast the wild bootstrap with the regular bootstrap using Monte Carlo numerical simulations for a number of diffusion scenarios. The regular and wild bootstrap methods are applied to human DTI data and empirical distributions are obtained for fractional anisotropy and the diffusion tensor eigensystem. Spatial maps of the estimated variability in the diffusion tensor principal eigenvector are provided. The wild bootstrap method can provide empirical distributions for tensor‐derived quantities, such as fractional anisotropy and principal eigenvector direction, even when the exact distributions are not easily derived. Hum Brain Mapp, 2008.

Q-ball imaging of macaque white matter architecture

Diffusion-weighted magnetic resonance imaging holds substantial promise as a technique for non-invasive imaging of white matter (WM) axonal projections. For diffusion imaging to be capable of providing new insight into the connectional neuroanatomy of the human brain, it will be necessary to histologically validate the technique against established tracer methods such as horseradish peroxidase and biocytin histochemistry. The macaque monkey provides an ideal model for histological validation of the diffusion imaging method due to the phylogenetic proximity between humans and macaques, the gyrencephalic structure of the macaque cortex, the large body of knowledge on the neuroanatomic connectivity of the macaque brain and the ability to use comparable magnetic resonance acquisition protocols in both species. Recently, it has been shown that high angular resolution diffusion imaging (HARDI) can resolve multiple axon orientations within an individual imaging voxel in human WM. This capability promises to boost the accuracy of tract reconstructions from diffusion imaging. If the macaque is to serve as a model for histological validation of the diffusion tractography method, it will be necessary to show that HARDI can also resolve intravoxel architecture in macaque WM. The present study therefore sought to test whether the technique can resolve intravoxel structure in macaque WM. Using a HARDI method called q-ball imaging (QBI) it was possible to resolve composite intravoxel architecture in a number of anatomic regions. QBI resolved intravoxel structure in, for example, the dorsolateral convexity, the pontine decussation, the pulvinar and temporal subcortical WM. The paper concludes by reviewing remaining challenges for the diffusion tractography project.

Abnormal cortical folding patterns within Broca's area in schizophrenia: Evidence from structural MRI

We compared cortical folding patterns between patients with schizophrenia and demographically-matched healthy controls in prefrontal and temporal regions of interest. Using the Freesurfer (http://surfer.nmr.mgh.harvard.edu) cortical surface-based reconstruction methodology, we indirectly ascertained cortical displacement and convolution, together, by measuring the degree of metric distortion required to optimally register cortical folding patterns to an average template. An area within the pars triangularis of the left inferior frontal gyrus (Brocas area) showed significantly reduced metric distortion in the patient group relative to the control group (p=0.0352). We discuss these findings in relation to the neurodevelopmental hypothesis and language dysfunction in schizophrenia.

An MRI study of age-related white and gray matter volume changes in the rhesus monkey

We applied the automated MRI segmentation technique Template Driven Segmentation (TDS) to dual-echo spin echo (DE SE) images of eight young (5-12 years), six middle-aged (16-19 years) and eight old (24-30 years) rhesus monkeys. We analyzed standardized mean volumes for 18 anatomically defined regions of interest (ROIs) and found an overall decrease from young to old age in the total forebrain (5.01%), forebrain parenchyma (5.24%), forebrain white matter (11.53%), forebrain gray matter (2.08%), caudate nucleus (11.79%) and globus pallidus (18.26%). Corresponding behavioral data for five of the young, five of the middle-aged and seven of the old subjects on the Delayed Non-matching to Sample (DNMS) task, the Delayed-recognition Span Task (DRST) and the Cognitive Impairment Index (CII) were also analyzed. We found that none of the cognitive measures were related to ROI volume changes in our sample size of monkeys.

Statistical group comparison of diffusion tensors via multivariate hypothesis testing

Diffusion tensor imaging (DTI) provides a powerful tool for identifying white matter (WM) alterations in clinical populations. The prevalent method for group‐level analysis of DTI is statistical comparison of the diffusion tensor fractional anisotropy (FA) metric. The FA metric, however, does not capture the full orientational information contained in the diffusion tensor. For example, the FA test is incapable of detecting group‐level differences in diffusion orientation when the level of anisotropy is unaffected. Here, we apply multivariate hypothesis testing procedures to the elements of the diffusion tensor as an alternative to univariate testing using FA. Both parametric and nonparametric tests are proposed with each choice carrying specific assumptions about the diffusion tensor model. Of particular interest is the Cramér test, which works on Euclidean interpoint distances and can be readily adapted to a specific non‐Euclidean framework by applying matrix logarithms to the diffusion tensors. Using Monte Carlo simulations, we show that multivariate tests can detect diffusion tensor principal eigenvector differences of 15 degrees with up to 80–90% power under typical design conditions. We also show that some multivariate tests are more sensitive to FA differences, when compared to a univariate test on FA, even if there is no principal eigenvector difference. The Cramér test, using the Euclidean interpoint distances, performed best under both simulation scenarios. When applying the Cramér test of the diffusion tensor in a clinical population with a history of migraine, a 169% increase was observed in the volume of a significant cluster compared to the univariate FA test. Magn Reson Med 57:1065–1074, 2007.

Boosting the sampling efficiency of q-Ball imaging using multiple wavevector fusion.

q‐Ball imaging (QBI) is a high‐angular‐resolution diffusion imaging (HARDI) method that is capable of resolving complex, subvoxel white matter (WM) architecture. QBI requires time‐intensive sampling of the diffusion signal and large diffusion wavevectors. Here we describe a reconstruction scheme for QBI, termed multiple wavevector fusion (MWF), that substantially boosts the sampling efficiency and signal‐to‐noise ratio (SNR) of QBI. The MWF reconstruction operates by nonlinearly fusing the diffusion signal from separate low and high wavevector acquisitions. The combination of wavevectors provides the benefits of the high SNR of the low wavevector signal and the high angular contrast‐to‐noise ratio (CNR) and peak separation of the high wavevector signal. The MWF procedure provides a framework for combining diffusion tensor imaging (DTI) and QBI. Numerical simulations show that MWF of DTI and QBI provides a more accurate estimate of the diffusion orientation distribution function (ODF) than QBI alone. The accuracy improvement can be translated into an efficiency gain of 274–377%. An intravoxel peak connectivity metric (IPCM) is presented that calculates the peak connectivity between an ODF and its neighboring voxels. In human WM, MWF reveals more detailed WM architecture than QBI as measured by the IPCM for all sampling schemes presented. Magn Reson Med 57:289–296, 2007.

Bilateral variation of subclavius muscle resembling subclavius posticus.

During routine anatomical dissection, a bilateral variation of the muscle subclavius was discovered with additional morphological features consistent with the muscle subclavius posticus. Attached medially to the first rib by tendon and to the clavicle by fibrous bands, the long triangular shaped muscle ran dorsal-laterally to attach onto the transverse scapular ligament and the coracoid process. The scapular insertion of the omohyoid muscle was just medial to this muscle, with some intermingling of fibers close to their insertions. In addition, the muscle on the left was split into two heads before inserting onto the scapula. Innervation was supplied by the nerve to the subclavius. We believe this muscle to be a hybrid of subclavius and subclavius posticus muscles, and we discuss the developmental origin of this rare subclavius variant, as well as the potential role this muscle may play in the development of thoracic outlet syndrome.

A heat map of superior cervical ganglion location relative to the common carotid artery bifurcation

BACKGROUND: Determining the superior cervical ganglions precise anatomical location for local anesthetic block, when stellate block is not feasible or is contraindicated, is difficult. METHODS: We dissected the superior cervical ganglion in 60 embalmed cadaveric specimens. Multiple regressions determined whether subject characteristics predicted the distance between the superior cervical ganglion and common carotid artery bifurcation and the superior cervical ganglion dimensional width and area. Based on these regressions, we mapped the ganglion and common carotid artery bifurcation using a pseudocolor statistical heat map. RESULTS: The statistical model significantly predicted the superior cervical ganglion–common carotid artery bifurcation distance (P = 0.01), and the superior cervical ganglion dimensional width (P = 0.02). CONCLUSION: This study determined that the common carotid artery bifurcation is a good landmark for localizing the superior cervical ganglion for anesthetic block.

The human temporalis muscle: superficial, deep, and zygomatic parts comprise one structural unit.

The structure of the temporalis muscle was examined in detail from cadaveric specimens (32 specimens from 16 subjects: 5 males, average age 80.6 years; 11 females, average age 88.6 years) and Computerized Tomography (CT) and T1‐weighted Magnetic Resonance (MR) images from normal clinical patients (10 females: average age 45.0 years). Three parts of the muscle were clearly delineated in all cadaveric specimens: (1) the classically recognized superficial part, (2) a zygomatic part, and (3) a complex deep part. In one female specimen, the superficial temporalis demonstrated extensive insertions into the zygomatic process and temporomandibular joint. The zygomatic temporalis originates from the zygomatic arch to insert into the superficial part of the temporalis as it inserts into the lateral surface of the coronoid process. In all specimens, the deep temporalis contained muscle bundles that originated from various crests along the anterior surface of the temporal fossa and inserted into the internal aspect of the coronoid process and retromolar triangle, interdigitating with the buccinator, mylohyoid, and superior constrictor muscles. The confluence of muscle fibers into the buccinator muscle was confirmed in all CT/MRI images. The deep and zygomatic parts described were regarded as accessory muscle bellies previously, but are demonstrably part of the temporalis muscle as a whole. Clin. Anat. 22:655–664, 2009.