T1 Mapping for Myocardial Fibrosis by Cardiac Magnetic Resonance Relaxometry-A Comprehensive Technical Review.

Cardiac magnetic resonance (CMR) imaging has been widely used to assess myocardial perfusion and scar and is the non-invasive gold standard for identification of focal myocardial fibrosis. However, the late gadolinium enhancement technique is limited in its accuracy for absolute quantification and assessment of diffuse myocardial fibrosis by technical and pathophysiological features. CMR relaxometry, incorporating T1 mapping, has emerged as an accurate, reproducible, highly sensitive, and quantitative technique for the assessment of diffuse myocardial fibrosis in a number of disease states. We comprehensively review the physics behind CMR relaxometry, the evidence base, and the clinical applications of this emerging technique.

Automatic hip cartilage segmentation from 3D MR images using arc-weighted graph searching.

Accurate segmentation of hip joint cartilage from magnetic resonance (MR) images offers opportunities for quantitative investigations of pathoanatomical conditions such as osteoarthritis. In this paper, we present a fully automatic scheme for the segmentation of the individual femoral and acetabular cartilage plates in the human hip joint from high-resolution 3D MR images. The developed scheme uses an improved optimal multi-object multi-surface graph search framework with an arc-weighted graph representation that incorporates prior morphological knowledge as a basis for segmentation of the individual femoral and acetabular cartilage plates despite weak or incomplete boundary interfaces. This automated scheme was validated against manual segmentations from 3D true fast imaging with steady-state precession (TrueFISP) MR examinations of the right hip joints in 52 asymptomatic volunteers. Compared with expert manual segmentations of the combined, femoral and acetabular cartilage volumes, the automatic scheme obtained mean (± standard deviation) Dice's similarity coefficients of 0.81 (± 0.03), 0.79 (± 0.03) and 0.72 (± 0.05). The corresponding mean absolute volume difference errors were 8.44% (± 6.36), 9.44% (± 7.19) and 9.05% (± 8.02). The mean absolute differences between manual and automated measures of cartilage thickness for femoral and acetabular cartilage plates were 0.13 mm (± 0.12) and 0.11 mm (± 0.11), respectively.

Effect of splinting and exercise on intraneural edema of the median nerve in carpal tunnel syndrome--an MRI study to reveal therapeutic mechanisms.

Splinting and nerve and tendon gliding exercises are commonly used to treat carpal tunnel syndrome (CTS). It has been postulated that both modalities reduce intraneural edema. To test this hypothesis, 20 patients with mild to moderate CTS were randomly allocated to either night splinting or a home program of nerve and tendon gliding exercises. Magnetic resonance images of the wrist were taken at baseline, immediately after 10 min of splinting or exercise, and following 1 week of intervention. Primary outcome measures were signal intensity of the median nerve at the wrist as a measure of intraneural edema and palmar bowing of the carpal ligament. Secondary outcome measures were changes in symptom severity and function. Following 1 week of intervention, but not immediately after 10 min, signal intensity of the median nerve was reduced by ≈ 11% at the radioulnar level for both interventions (p = 0.03). This was accompanied by a mild improvement in symptoms and function (p < 0.004). A similar reduction in signal intensity is not observed in patients who only receive advice to remain active. No changes in signal intensity were identified further distally (p > 0.28). Ligament bowing remained unchanged (p > 0.08). Intraneural edema reduction is a likely therapeutic mechanism of splinting and exercise.

Pearls and pitfalls of magnetic resonance imaging of the upper extremity.

Magnetic resonance imaging (MRI) is capable of producing images in any anatomical plane, visualizing and analyzing a variety of tissue characteristics, as well as quantifying blood flow and metabolic functions. Although MRI details of compact bone and calcium are poor when compared to those taken with plain radiography or computed tomography, its high soft tissue contrast discrimination and multiplanar imaging capabilities are significant advantages. Musculoskeletal anatomy and neurovascular bundles are well delineated. The advent of MRI has revolutionized the clinician's ability to confirm a proper diagnosis for musculoskeletal problems, which has led to more directed, specific rehabilitative protocols. However, the value of MRI to rehabilitative professionals has been even greater in its ability to identify serious, more uncommon pathologies, such as in those with underlying infection, fracture, or tumor, that require immediate care and are considered to be beyond their scope of practice. Furthermore, MRI, with its precise delineation of fat, muscle, and bone, is an ideal candidate for imaging of muscle disease or injury and has emerged as the method of choice for the detection of early cartilage wear in young patients, such as osteoarthritis. Finally, this imaging modality can avoid radiation exposure in a predominantly younger patient cohort commonly affected by musculoskeletal diseases. The aim of this paper is to consider how physical therapists may take advantage of the diagnostic value of MRI of the upper limb, while avoiding the pitfalls of misinterpretation of images as a result of technical issues, pathological changes, or normal variants.

Neural mechanisms underlying spatial realignment during adaptation to optical wedge prisms.

Visuomotor adaptation to a shift in visual input produced by prismatic lenses is an example of dynamic sensory-motor plasticity within the brain. Prism adaptation is readily induced in healthy individuals, and is thought to reflect the brain's ability to compensate for drifts in spatial calibration between different sensory systems. The neural correlate of this form of functional plasticity is largely unknown, although current models predict the involvement of parieto-cerebellar circuits. Recent studies that have employed event-related functional magnetic resonance imaging (fMRI) to identify brain regions associated with prism adaptation have discovered patterns of parietal and cerebellar modulation as participants corrected their visuomotor errors during the early part of adaptation. However, the role of these regions in the later stage of adaptation, when 'spatial realignment' or true adaptation is predicted to occur, remains unclear. Here, we used fMRI to quantify the distinctive patterns of parieto-cerebellar activity as visuomotor adaptation develops. We directly contrasted activation patterns during the initial error correction phase of visuomotor adaptation with that during the later spatial realignment phase, and found significant recruitment of the parieto-cerebellar network--with activations in the right inferior parietal lobe and the right posterior cerebellum. These findings provide the first evidence of both cerebellar and parietal involvement during the spatial realignment phase of prism adaptation.

A magnetic resonance imaging investigation of the transversus abdominis muscle during drawing-in of the abdominal wall in elite Australian Football League players with and without low back pain.

STUDY DESIGN: Single-blinded quasi-experimental study. OBJECTIVE: To investigate the ability of elite football players with and without low back pain (LBP) to voluntarily draw-in the abdominal wall. BACKGROUND: While there has been considerable debate regarding the contribution of the transversus abdominis (TrA) muscle to control the lumbar spine and pelvis, there is evidence that retraining motor control of the deep trunk muscles is commensurate with decreases in LBP. Magnetic resonance imaging (MRI) has been used to assess the TrA muscle during the draw-in maneuver, with the contraction of the TrA muscle reducing the circumference of the trunk. Impairments in performance of the draw-in maneuver have been shown in people with LBP. METHODS: Forty-three elite players from a team in the Australian Football League were allocated to 3 groups: those with "no LBP," "a history of LBP but no current LBP," or "current LBP." MRI was used to image the cross-sectional area (CSA) of the trunk at the level of the L3-4 disc at the start and end of the draw-in maneuver. RESULTS: There was a significant decrease in the CSA of the trunk with the performance of the draw-in maneuver (P<.001). Subjects in the "no LBP" group were better able to "draw-in" the abdominal wall than subjects with current LBP (P = .015). CONCLUSIONS: This study provides evidence of an altered ability to draw-in the abdominal wall in footballers with current LBP. Retraining contraction of the TrA muscle may constitute one part of an exercise-therapy approach for athletes with current LBP.

Altered white matter diffusion anisotropy in normal and preterm infants at term-equivalent age.

To investigate white matter (WM) development, voxelwise analyses of diffusion tensor MRI (DTMRI) data, acquired from 12 very preterm and 11 preterm infants with gestational ages (GA) ranging from 25 to 29 and 29 to 32 weeks, respectively, and 10 newborn normal term infants were performed. T(2) relaxation measures were also generated to assess brain water content. Compared with newborn term infants, very preterm infants were found to possess reduced fractional anisotropy (FA) within the frontal lobe, and a number of anterior and posterior commissural pathways. Preterm infants possessed reduced FA mainly within the posterior regions of the corpus callosum. Unexpectedly, we observed significantly reduced FA and increased T(2) within a number of corticospinal projections in the newborn term infants compared to the preterm groups. This finding may reflect increased water concentration and/or a lowering of FA due to the presence of crossing interhemispheric WM projections. These findings indicate that care should be taken when interpreting FA indices without knowledge of the possible effects of water concentration in the newborn infant brain.

Point injection as an alternative acupuncture technique--an exploratory study of responses in healthy subjects.

INTRODUCTION: Point injection as a therapeutic technique is well documented, but its physiological effects have not been formally compared with traditional acupuncture. One aim of this study was to compare the effects of the two techniques at one acupuncture point, as a step towards understanding the mode of action of point injection and validating its clinical use. A second aim was to explore whether repeated point injection at the same site might provide a way of increasing the dose of stimulation, in the hope of identifying a dose response curve which could be an alternative strategy to placebo control in demonstrating the biological effects of acupuncture. METHODS: Sixty nine healthy subjects (age range 18-56 years, mean 29.9; 48 females) completed the study, which employed a counterbalanced experimental design with two stimulation sessions of LI4 approximately one week apart. One half of the participants received point injection first, and the other half received traditional acupuncture first. Baseline physiological data were recorded, then measurements were made before, during and after stimulation; each subject also reported needle sensation (de qi). The measures were heart rate, derived pressure rate product and mean arterial pressure. RESULTS: Although stronger sensations of de qi were reported with point injection, no significant differences were found for mean heart rate (HR), pressure rate product (PRP) and mean arterial pressure (MAP) before and after stimulation by the two techniques. No subject gender or age bias was encountered and previous exposure to acupuncture had no effect on outcome. Power spectral analysis of heart rate variability (HRV) made on data from a small subset (n=10) of this cohort also showed no significant differences in autonomic response. CONCLUSION: Point injection and traditional acupuncture seem to provoke similar physiological responses, although the greater needle sensation seen with point injection might indicate it could have more powerful clinical effects. Further studies of repeated point injection are necessary to indicate whether this technique may provide a method of increased strength of point stimulation, as an alternative to traditional needling in acupuncture research.

Automated syringe driver for acupoint injection in functional MRI studies: a case for quantified point injection in neuroimaging studies of acupuncture.

The investigation of proposed acupuncture models is experiencing increasing interest particularly since the inception of functional neuroimaging in the early 1990s, but difficulty in providing acceptable controls has been an ongoing limitation. The use of titrated stimulation to generate a dose response is implied in the nature of the stimulus and the timing of the response. To address the complexity of delivering an accurate stimulus during an imaging study while simultaneously maintaining synchrony and recording stimulus parameters, stimulus delivery needs to be an automated task. This report presents the design and general description of a system capable of delivering acupoint stimulation by injection of precisely timed and measured saline doses while simultaneously interfaced to biomonitoring or neuroimaging instruments. The results of instrument validation in a clinical environment are presented, along with a discussion of the usefulness and limitations of the device.

Evidence of altered prefrontal-thalamic circuitry in schizophrenia: an optimized diffusion MRI study.

MRI diffusion tensor imaging (DTI), optimized for measuring the trace of the diffusion tensor, was used to investigate microstructural changes in the brains of 12 individuals with schizophrenia compared with 12 matched control subjects. To control for the effects of anatomic variation between subject groups, all participants' diffusion images were nonlinearly registered to standard anatomical space. Significant statistical differences in mean diffusivity (MD) measures between the two groups were determined on a pixel-by-pixel basis, using Gaussian random field theory. We found significantly elevated MD measures within temporal, parietal and prefrontal cortical regions in the schizophrenia group (P > 0.001), especially within the medial frontal gyrus and anterior cingulate. The dorsal medial and anterior nucleus of the thalamus, including the caudate, also exhibited significantly increased MD in the schizophrenia group (P > 0.001). This study has shown for the first time that MD measures offer an alternative strategy for investigating altered prefrontal-thalamic circuitry in schizophrenia.

Assessment of dynamic susceptibility contrast cerebral blood flow response to amphetamine challenge: a human pharmacological magnetic resonance imaging study at 1.5 and 4 T.

Pharmacological MRI (phMRI) techniques can be used to monitor the neurophysiological effects of central nervous system (CNS) active drugs. In this study, we investigated whether dynamic susceptibility contrast (DSC) perfusion imaging employing the use of superparamagnetic iron oxide nanoparticles (Resovist) could be used to measure hemodynamic response to d-amphetamine challenge in human subjects at both 1.5 and 4 T. Significant changes in cerebral blood flow (CBF) were found in focal regions associated with the nigrostriatal circuit and mesolimbic and mesocortical dopaminergic pathways. More significant CBF responses were found at higher field strength, mainly within striatal structures. The results from this study indicate that DSC perfusion imaging using Resovist can be used to assess the efficacy of CNS-active drugs and may play a role in the development of novel psychiatric therapies at the preclinical level.

Improving the prediction of final infarct size in acute stroke with bolus delay-corrected perfusion MRI measures.

PURPOSE: To investigate whether bolus delay-corrected dynamic susceptibility contrast (DSC) perfusion MRI measures allowed a more accurate estimation of eventual infarct volume in 14 acute stroke patients using a predictive tissue classifier algorithm. MATERIALS AND METHODS: Tissue classification was performed using a expectation maximization and k-means clustering algorithm utilizing diffusion and T2 measures (diffusion-weighted imaging [DWI], apparent diffusion coefficient [ADC], and T2) combined with uncorrected perfusion measures cerebral blood flow ((CBF) and mean transit time [MTT]), bolus delay-corrected perfusion measures (cCBF and cMTT), and bolus delay-corrected perfusion indices (cCBF and cMTT with bolus delay). RESULTS: The mean similarity index (SI), a kappa-based correlation statistic reflecting the pixel-by-pixel classification agreement between predicted and 30-day T2 lesion volumes, were 0.55 +/- 0.19, 0.61 +/- 0.15 (P < 0.02) and 0.60 +/- 0.17 (P <0.03), respectively. Spearman's correlation coefficients, comparing predicted and final lesion volumes were 0.56 (P < 0.05), 0.70 (P < 0.01), and 0.84 (P < 0.001), respectively. We found a more significant correlation between predicted infarct volumes derived from bolus delay-corrected perfusion measures than from conventional perfusion measures when combined with diffusion measures and compared with final lesion volumes measured on 30-day T2 MRI scans. CONCLUSION: Bolus delay-corrected perfusion measures enable an improved prediction of infarct evolution and evaluation of the hemodynamic status of neuronal tissue in acute stroke.

Correlation of quantitative EEG in acute ischemic stroke with 30-day NIHSS score: comparison with diffusion and perfusion MRI.

BACKGROUND AND PURPOSE: Magnetic resonance imaging (MRI) methods such as diffusion- (DWI) and perfusion-weighted (PWI) imaging have been widely studied as surrogate markers to monitor stroke evolution and predict clinical outcome. The utility of quantitative electroencephalography (qEEG) as such a marker in acute stroke has not been intensively studied. The aim of the present study was to correlate ischemic cortical stroke patients' clinical outcomes with acute qEEG, DWI, and PWI data. MATERIALS AND METHODS: DWI and PWI data were acquired from 11 patients within 7 and 16 hours after onset of symptoms. Sixty-four channel EEG data were obtained within 2 hours after the initial MRI scan and 1 hour before the second MRI scan. The acute delta change index (aDCI), a measure of the rate of change of average scalp delta power, was compared with the National Institutes of Health Stroke Scale scores (NIHSSS) at 30 days, as were MRI lesion volumes. RESULTS: The aDCI was significantly correlated with the 30-day NIHSSS, as was the initial mean transit time (MTT) abnormality volume (rho=0.80, P<0.01 and rho=0.79, P<0.01, respectively). Modest correlations were obtained between the 15-hour DWI lesion volume and both the aDCI and 30-day NIHSSS (rho=0.62, P<0.05 and rho=0.73, P<0.05, respectively). CONCLUSIONS: In this small sample the significant correlation between 30-day NIHSSS and acute qEEG data (aDCI) was equivalent to that between the former and MTT abnormality volume. Both were greater than the modest correlation between acute DWI lesion volume and 30-day NIHSSS. These preliminary results indicate that acute qEEG data might be used to monitor and predict stroke evolution.