Concept for gradient-free MRI on twin natural slices.

OBJECTIVE: The design of an MRI for use in space requires that the hardware be kept to an absolute minimum in terms of mass, complexity, and power. In addition, NASA requirements are that the external stray field needs to be less than 3.2 Gauss, 7 cm from the MRI enclosure. THEORY: RF encoding designs with Halbach magnets offer the best chance of meeting those requirements. Spatially non-uniform magnetic fields with foliations of isomagnetic surfaces, or natural slices, may be used to provide slice selection, and to reduce further the hardware complexity, for TRansmit Array Spatial Encoding (TRASE) Magnetic Resonance Imaging (MRI) or potentially for other radio frequency (RF) encoding methods. The design of such non-uniform magnetic fields in a Halbach configuration with built-in axial gradients leads to pairs of isomagnetic surfaces centered on either side of a central maximum field strength slice. If TRASE images from slices other than the central isomagnetic surface are desired, then the Nuclear Magnetic Resonance (NMR) signals originating from the twin natural slices must be separated during image reconstruction. Here, a design for simultaneously imaging on twin slices in such an inhomogeneous magnetic field using multiple receiver coils with spatially varying RF profiles is described mathematically and numerical simulation examples are given. DESIGN APPROACH: To achieve RF encoding on the natural slices, at least three TRASE transmit coils are required. Here a solution with twisted solenoid coils is given. To achieve the twin slice separation at least two receive coils are required. Here a solution with two solenoids is given. DISCUSSION: The MRI design presented here uses a combination of RF encoding (TRASE), a spatial encoding magnetic field (SEM, pairs of natural slices) and receive coil spatial profiles to encode enough information into the NMR signal for image slice reconstruction. The design presented here enables using Halbach magnets with a built-in axial gradient to be used for MRI. CONCLUSION: The result is a new gradient-free TRASE MRI design capable of imaging pairs of electronically selectable axial slices.

Best practice interprofessional stroke care collaboration and simulation: The student perspective.

Interprofessional practice (IPP) is the accepted standard of care for clients following a stroke. A brief, embedded and evidence-based IPP team simulation was designed to address stroke care knowledge and IPP competencies for students within limited curriculum space. Each team was required to construct a collaborative care plan for their patient during the simulation and submit the care plan for evaluation of best practice stroke care knowledge and implementation with evidence of interprofessional collaboration (IPC). A total of 302 students (274 on-site, 28 by distance technology) representing four professions comprised of 55 teams took part in this experience. Post-simulation, voluntary and anonymous programme evaluations were completed using the standardised interprofessional collaborative competency assessment scale (ICCAS) and open-ended free-text responses to five questions. There was a significant improvement for all pre-post ratings on the ICCAS regardless of profession or previous interprofessional experience. Additionally, the open-ended responses indicated perceived changes to role clarification, communication, and teamwork. The combined interpretation of the programme evaluation results supports interprofessional team simulation as an effective and efficient learning experience for students regardless of previous interprofessional experience, and demonstrated positive changes in stroke best-practice knowledge and IPC competencies.

The effects of coupled B1 fields in B1 encoded TRASE MRI - A simulation study.

Transmit Array Spatial Encoding (TRASE) is a novel MRI technique that encodes spatial information by introducing phase gradients in the transmit RF (B1) magnetic field. Since TRASE relies on the use of multiple RF fields (B1 fields with different phase gradients) for k-space traversal, a TRASE pulse sequence requires RF pulses that are produced by switching between the transmit coils (B1 fields). However, interactions among the transmit RF coils can cause un-driven coils to produce unwanted B1 fields that impair the spatial encoding. Therefore, TRASE is sensitive to B1 field perturbations arising from inductive coupling among the RF transmit coils and any B1 field isolation (coil decoupling) technique requires an understanding of the effects of the B1 field interactions. The purpose of this study was to investigate the effects of B1 field coupling using Bloch equation based simulations and to determine the acceptable level of B1 field interactions for 2D TRASE imaging. The simulations show that 2D TRASE MRI (using a 3-coil setup) displays ideal performance for pairwise coupling constant lower than k = 0.01 while having acceptable performance up to k = 0.1. This translates into S12 measurements of range ~(- 50 dB to -30 dB) required for successful 2D TRASE MRI in this study. This result is of crucial importance for designers of practical TRASE transmit array systems.

TRASE 1D sequence performance in imperfect B1 fields.

Transmit Array Spatial Encoding (TRASE) is an MRI technique that uses radio-frequency (RF) magnetic field (B1) phase gradients for spatial encoding. A TRASE pulse sequence consists of a long echo train in which each echo samples a different k-space point. Due to the need for accurate refocusing, TRASE imaging performance depends on |B1| homogeneity. Although the CPMG echo train is often relied on to provide immunity against B1 flip angle errors, this does not apply to TRASE echo trains. Due to the spatially dependent B1 phases involved in TRASE imaging, the CPMG condition, where all spins flip about the y-axis in the rotating frame, can only be achieved at one single location within the sample. Moreover, CPMG only preserves one component of the transverse magnetization, the y-component, whereas TRASE requires both components to be retained. Here we investigate the performance of a set of variants of a 1-dimensional (1D) TRASE sequence under conditions of |B1| errors. We varied the B1 transmit pulse RF waveform phases in an effort to optimize the TRASE imaging point spread function (PSF). The performance of 256 sequence variants, including those previously reported in the literature was studied. Both Bloch equation simulations and experimental confirmations were completed. Off-resonance (B0 inhomogeneity) effects were not considered so that the effects of B1 inhomogeneity alone could be understood. Results show that, using optimum transmit pulse phases, high quality image encoding is achievable over ∼90% of the Nyquist field-of-view (FOV) for a practically realizable variation in B1 amplitude (Δ|B1|⩽±11%). This improves significantly upon the performance of a previously-reported sequence which generated ∼75% usable FOV within the Nyquist FOV.

Mapping the semantic homunculus: a functional and behavioural analysis of overt semantic generation.

Previous neuroanatomical research has shown that semantic processing of action-related language activates the premotor, motor, and sensory cortices somatotopically (e.g., Tettamanti et al., J Cognitive Neurosci. 2005;17(2): 273-281, using a listening task, and Hauk et al., Neuron. 2004;41:301-307 and Pulvermuller et al., Eur J Neurosci 2005;21:793-797; J Cognitive Neurosci 2005;17(6):884-892 using a silent reading task). We examined this somatotopic semantics hypothesis using an overt semantic generation task (i.e., participants generated aloud their own personal description of how they would interact with target object words), rather than semantic comprehension as examined in previous research, so as to provide a stronger test of the hypothesis under conditions that tap one's own semantic knowledge about interacting with objects. Experiment 1 used functional Magnetic Resonance Imaging (fMRI) to examine somatotopically organized activation in the premotor cortex for an overt semantic generation task, using targets that naturally involve either arm interactions or leg interactions. Consistent with previous research, our results showed that semantic processing related to object interaction involves the motor, premotor and sensory cortices in a somatotopic fashion. Previous behavioural research has shown a response advantage in lexical decision for words with multiple meanings or features, which diminishes with tasks that decrease semantic involvement (e.g., Borowsky and Masson, J Exp Psychol: Learn Memory Cognit 1996; 22(1):63-85; Pexman et al., Psychon Bull Rev 2002;9(3): 542-549). Experiment 2 evaluated whether semantic generation response times (total duration of response) display a complexity advantage (i.e., faster response times for more complex objects), and whether complexity ratings were related to the volume of brain activation during the task. Results from this behavioural experiment revealed a significant negative relationship between the total duration of response (i.e., the total amount of time taken to respond to the stimuli) and object complexity for leg objects (a semantic complexity advantage), but not for arms. This suggests that the smaller repertoire of possible interactions with leg objects requires a greater reliance on semantic knowledge in order to respond in the semantic generation task. This interpretation was further supported by a greater volume of brain activation in the premotor cortex for arm objects versus leg objects. The response times from Experiment 1 were also compared to the semantic complexity ratings gathered in Experiment 2 to determine if response times in the fMRI environment were affected by how complex an object is.

The relationship between naming reaction time and functional MRI parameters in Broca's area.

We examined the correlation between behavioural reaction time and functional imaging parameters of the blood oxygenated level dependent (BOLD) response in Broca's Area during a word identification task, and whether the correlation [Magnetic Resonance Imaging 22 (2004) 451-455] varies as a function of four stimulus types: regular words (REGs) (e.g., hint), irregular words (IRRs) (e.g., pint), nonwords (NWs) (e.g., bint), and pseudohomophones (PHs) (e.g., pynt). Participants named letter strings aloud during a functional magnetic resonance imaging study. Naming reaction times were recorded during regular gaps in image acquisition, and BOLD parameters were extracted via a Tikhonov regularized BOLD analysis technique. The results revealed that only PH reaction times were correlated with BOLD width, providing evidence that Broca's area supports phonetic decoding accompanied with phonological lexical access. In addition, we advanced the development of equation-based models of cognitive behaviour and neurophysiology, whereby we showed that the relationship of mathematical independence that exists for predicting REG accuracy, given IRR and NW or PH naming accuracy, was present for naming reaction time, BOLD width, BOLD time to peak, and BOLD intensity. Therefore, we provide converging behavioural and neuroanatomical evidence for a mathematically independent relationship between sight vocabulary and phonetic decoding systems, consistent with a dual-route model of reading.

Magnetic resonance imaging with RF encoding on curved natural slices.

While the idea of using spatial encoding fields (SEM) for image formation has been proven, conventional wisdom still holds that a magnetic resonance imaging (MRI) system begins with a highly uniform magnetic field. In particular, radio frequency (RF) encoding MRIs designed and tested to date have largely used uniform magnetic fields. Here we demonstrate magnetic resonance imaging in a magnetic field with a built-in gradient that gives non-planar slices - curved surfaces - when the nuclear spins are excited with narrow band RF pulses. Image encoding on these naturally occurring non-planar slices was accomplished with RF encoding using a non-linear spatially varying B1 phase gradient. The imaging methods were demonstrated on a small prototype MRI instrument. The MRI has no switched magnetic field gradients - it is "gradient-free". A low field gradient-free MRI with low mass permanent magnets and simple, low power, RF encoding hardware is ideal for deployment on the International Space Station for the study of astronaut muscle and bone mass loss. Gradient-free natural slice encoding MRI designs would also be portable enough for application in remote terrestrial locations, in emergency rooms and in operating rooms where they can be used with minimally invasive and robotic surgery.

Composite pulses for RF phase encoded MRI: A simulation study.

BACKGROUND: In B1 encoded MRI, a realistic non-linear phase RF encoding coil will generate an inhomogeneous B1 field that leads to spatially dependent flip angles. The non-linearity of the B1 phase gradient can be compensated for in the reconstruction, but B1 inhomogeneity remains a problem. The effect of B1 inhomogeneity on tip angles for conventional, B0 encoded MRI, may be minimized using composite pulses. The objective of this study was to explore the feasibility of using composite pulses with non-linear RF phase encoding coils and to identify the most appropriate composite pulse scheme. METHODS: RF encoded signals were simulated via the Bloch equation for various symmetric, asymmetric and antisymmetric composite pulses. The simulated signals were reconstructed using a constrained least squares method. RESULTS: Root mean square reconstruction errors varied from 6% (for an asymmetric composite pulse) to 9.7% (for an antisymmetric composite pulse). CONCLUSION: An asymmetric composite pulse scheme created images with fewer artifacts than other composite pulse schemes in inhomogeneous B0 and B1 fields making it the best choice for decreasing the effects of spatially varying flip angles. This is contrary to the conclusion that antisymmetric composite pulses are the best ones to use for spin echo sequences in conventional, B0 encoded, MRI.

A Network Analysis of Depressive Symptoms in Individuals Seeking Treatment for Chronic Pain.

OBJECTIVES: Major depression in the context of chronic pain has been conceptualized implicitly as a latent variable, in which symptoms are viewed as manifestations of an underlying disorder. A network approach provides an alternative model and posits that symptoms are causally connected, rather than merely correlated, and that disorders exist as systems, rather than as entities. The present study applied a network analysis to self-reported symptoms of major depression in patients with chronic pain. The goals of the study were to describe the network of depressive symptoms in individuals with chronic pain and to illustrate the potential of network analysis for generating new research questions and treatment strategies. MATERIALS AND METHODS: Patients (N=216) admitted to an interdisciplinary chronic pain rehabilitation program provided symptom self-reports using the Patient Health Questionnaire-9. Well-established network analyses methods were used to illustrate the network of depressive symptoms and determine the centrality of each symptom (ie, the degree of connection with other symptoms in the network). RESULTS: The most central symptoms were difficulty concentrating, loss of interest or pleasure, depressed mood, and fatigue, although the relative position of each symptom varied slightly, depending on the centrality measure considered. DISCUSSION: Consistent with past research with patients undergoing treatment for major depression, the current findings are supportive of a model in which depressive symptoms are causally connected within a network rather than being manifestations of a common underlying disorder. The research and clinical implications of the findings, such as developing treatments targeting the most central symptoms, are discussed.

Nuclear magnetic resonance spectroscopy of bovine ovarian follicular fluid at four selected times of the oestrous cycle.

The objective of the study was to determine if nuclear magnetic resonance (NMR) spectral features of ovarian follicular fluid were correlated with the physiological status of follicles so that we could assess the feasibility of using NMR spectroscopy during assisted reproduction therapy. Thirty-five sexually mature, nullparious heifers were monitored by transrectal ultrasonography to assess their follicle wave status during the oestrous cycle. Ovariectomies were performed on Day 3 of wave 1 (D3W1, n = 10), Day 6 of wave 1 (D6W1, n = 9), Day 1 of wave 2 (D1W2, n = 9), or in the immediate preovulatory period of at least 17 days after ovulation (De17, n = 9). Follicle status was determined to be dominant or subordinate. Follicular fluid was extracted from the follicles and NMR spectra were collected. Principal components were extracted from ratios of line amplitudes and tested for effects of follicle status (dominant v. subordinate) and cycle time point (D1W3, D1W6, D1W2 and De17) using multivariate analysis of variance. For most line ratio combinations, main effects of status, time point and their interaction were found (P < 0.05). We concluded that NMR spectra may be used for the determination of ovarian follicle physiological status.

Least squares reconstruction of non-linear RF phase encoded MR data.

PURPOSE: The numerical feasibility of reconstructing MRI signals generated by RF coils that produce B1 fields with a non-linearly varying spatial phase is explored. THEORY: A global linear spatial phase variation of B1 is difficult to produce from current confined to RF coils. Here we use regularized least squares inversion, in place of the usual Fourier transform, to reconstruct signals generated in B1 fields with non-linear phase variation. METHODS: RF encoded signals were simulated for three RF coil configurations: ideal linear, parallel conductors and, circular coil pairs. The simulated signals were reconstructed by Fourier transform and by regularized least squares. RESULTS: The Fourier reconstruction of simulated RF encoded signals from the parallel conductor coil set showed minor distortions over the reconstruction of signals from the ideal linear coil set but the Fourier reconstruction of signals from the circular coil set produced severe geometric distortion. Least squares inversion in all cases produced reconstruction errors comparable to the Fourier reconstruction of the simulated signal from the ideal linear coil set. CONCLUSION: MRI signals encoded in B1 fields with non-linearly varying spatial phase may be accurately reconstructed using regularized least squares thus pointing the way to the use of simple RF coil designs for RF encoded MRI.

An application of Lacker's mathematical model for the prediction of ovarian response to superstimulation.

Introduction. A mathematical model of ovarian follicular growth is applied to the problem of predicting ovarian response in a superstimulation protocol. Methods. Fifty-four women enrolled in an ovarian superstimulation program of therapy for the amelioration of idiopathic infertility had their ovarian cycles synchronized by taking Demulen 30 for two weeks prior to the study. Daily ultrasonographic imaging, measurements of serum estradiol and doses of hMG began on day 5 after the patients stopped taking Demulen. The diameters of individual follicles were measured and followed daily. When the largest follicle attained a diameter of 19 mm, hCG was given to induce ovulation. Individual follicle growth data were fit to a mathematical model of ovarian follicle maturation and the resulting parameters were used to classify patients into low and high ovarian response groups. Results. The parameters computed from the mathematical model fit were found to be predictive of ovarian response with a sensitivity of 71% and a specificity of 70%. The parameters were also meaningful within the context of the original mathematical model and have value for determining how doses of hMG may be adjusted during the course therapy to increase the ovarian response in individuals. Conclusion. Mathematical modeling of ultrasonographically derived follicular growth data has significant potential for clinical application in ovarian superstimulation protocols. The method of fitting follicular growth data to a mathematical follicle maturation surface furthermore provides a straightforward approach for the characterization of ovarian follicular dynamics in general.

Cyclic generalized projection MRI.

Progress in the development of portable MRI hinges on the ability to use lightweight magnets that have non-uniform magnetic fields. An image encoding method and mathematical procedure for recovering the image from the NMR signal from non-uniform magnets with closed isomagnetic contours is given. Individual frequencies in an NMR signal from an object in a non-uniform magnetic field give rise to integrals of the object along contours of constant magnetic field: generalized projections. With closed isomagnetic field contours a simple, cyclic, direct reconstruction of the image from the generalized projections is possible when the magnet and RF transmit coil are held fixed relative to the imaged object while the RF receive coil moves. Numerical simulations, using the Shepp and Logan mathematical phantom, were completed to show that the mathematical method works and to illustrate numerical limitations. The method is numerically verified and exact reconstruction demonstrated for discrete mathematical image phantoms. Correct knowledge of the RF receive field is necessary or severe image distortions will result. The cyclic mathematical reconstruction method presented here will be useful for portable MRI schemes that use non-uniform magnets with closed isomagnetic contours along with mechanically or electronically moving the RF receive coils.

Diffusion-Weighted Magnetic Resonance Imaging Attenuation Factors and Their Selection for Cancer Diagnosis and Monitoring.

Diffusion-weighted imaging (DWI) is based on the detection of water molecule movement in interstitial and intracellular space, and that motion may be restricted in ischemia and in tumors. An early diagnosis and characterization of several cancer related diseases is possible with DWI. Diffusion-weighted images are therefore important for patient management. Knowledge of the technical requirements for DWI, including a suitable selection of b-values for differentiating between perfusion and true diffusion, as well as an understanding of the advantages and limitations of different b-values selections, is necessary to obtain reliable diagnostic results. The aim of this article is to review the fundamentals of the DWI technique, the common protocols used, b-value selection, and DWI's main contribution to neoplasm detection and staging.

A cluster analytic examination and external validation of psychopathic offender subtypes in a multisite sample of Canadian federal offenders.

The present study is a cluster analytic examination and validation of psychopathic offender subtypes from 4 combined samples of Canadian federally incarcerated offenders, most of whom were serving sentences for violent offenses. The men were rated on the Hare Psychopathy Checklist-Revised (PCL-R; Hare, 1991, 2003) on the basis of comprehensive file information and 314 cases were extracted using a PCL-R total cut score of 25. Cluster analysis of the 4 PCL-R facets converged at a 2-cluster solution: a primary subtype characterized by prominent interpersonal and affective features of psychopathy and a secondary subtype characterized by comparatively few interpersonal features and high scores on the remaining facets. Validation analyses found that the vast majority of primary psychopathic offenders (74.1%) were White or of non-Aboriginal descent in contrast to the secondary subtype (47.6%). Secondary psychopathic offenders tended to be actuarially higher risk, have greater criminogenic needs, and to make greater amounts of treatment change on criminogenic targets; however, contrary to expectations, within-treatment changes from a violence reduction program were significantly associated with reductions in violent recidivism for primary, but not secondary, variants. There were few differences in rates of recidivism between the groups overall; secondary variants had higher rates of sexual violence which was largely accounted for by individual differences in baseline static risk. Implications for risk assessment, treatment planning, and the classification and etiology of primary and secondary psychopathy are discussed.

Dissociating semantic and perceptual components of synaesthesia: behavioural and functional neuroanatomical investigations.

Colour digit synaesthetes experience atypical dual perceptions wherein achromatic digits are perceived along with coloured photisms. Recent studies have employed Stroop or priming tasks and exhibited interference or facilitation in synaesthesia [Nature 410 (2001) 580-582; Perception 28 (1999) 651-664]. We compared a synaesthete to a semantic control with arbitrary colour-number associations and demonstrated that these tasks do not elicit effects unique to synaesthesia. In contrast, we present functional neuroimaging data that clearly differentiates between these two conditions.

Magnetic resonance image attributes of the bovine corpus luteum during development and regression.

To determine whether magnetic resonance (MR) image attributes of the corpus luteum (CL) reflect its physiologic status at different phases of the bovine ovarian cycle, we analyzed the numerical pixel values (NPVs), relaxation rates, proton densities (PDs), and apparent diffusion coefficients (ADCs) from T(1)-, T(2)-, and diffusion-weighted in vitro images and maps of the CL acquired at defined phases of luteal function. Ovaries were removed and serum samples taken on days 3, 6, and 10, or >/=17 (day 0 = ovulation), representing metestrus (n = 10), early diestrus (n = 7), mid-diestrus (n = 9), and proestrus (n = 7), respectively. Regions of interest (ROIs) in each quadrant of the CL (which occupied at least 20% of the quadrant) were selected for analysis. Three MR image slices were analyzed: the slice with the greatest cross-sectional area of the CL, and the slices acquired immediately before and after that slice. The mean NPVs of the CL in T(1)-weighted images increased at each phase from metestrus (1,104 +/- 40 msec) to early diestrus (1,119 +/- 77 msec), to late diestrus (1,206 +/- 43 msec) and proestrus (1446 +/- 80 msec; P < 0.001). The mean NPVs in T(1)-weighted images were higher in regressing CL (proestrous) than in any other phase (P < 0.002). Grayscale heterogeneity of CL in T(1)-weighted images tended to increase during regression (P < 0.07). Regressing CL (proestrus) exhibited higher T(1)-weighted mean NPVs (P < 0.01) and tended to have greater heterogeneity (P < 0.06) than growing (metestrus) and mature (diestrus) CL, even though similar progesterone concentrations were observed. The increased brightness and heterogeneity of regressing CL in T(1)-weighted images appeared to be correlated with increased connective tissue and triglyceride content and decreased vascularity. It is anticipated that diagnostic markers for luteal viability and atresia in the in vitro bovine model will be applied to in vivo studies in women.

FMRI of two measures of phonological processing in visual word recognition: ecological validity matters.

Previous functional magnetic resonance imaging (fMRI) studies have investigated the role of phonological processing by utilizing nonword rhyming decision tasks (e.g., Pugh et al., 1996). Although such tasks clearly engage phonological components of visual word recognition, it is clear that decision tasks are more cognitively involved than the simple overt naming tasks, which more closely map onto normal reading behavior. Our research aim for this study was to examine the advantages of overt naming tasks for fMRI studies of word recognition processes. Process models are presented to highlight the similarities and differences between two cognitive tasks that are used in the word recognition literature, pseudohomophone naming (e.g., pronounce BRANE) and rhyming decision (e.g., do LEAT and JEAT rhyme?). An fMRI study identified several differences in cortical activation associated with the differences observed in the process models. Specifically, the results show that the overt naming task involved the insular cortex and inferior frontal gyrus, whereas the rhyming decision task engaged the temporal-parietal regions. It is argued that future fMRI research examining the neuroanatomical components of basic visual word recognition utilize overt naming tasks.

A neuroanatomical examination of embodied cognition: semantic generation to action-related stimuli.

The theory of embodied cognition postulates that the brain represents semantic knowledge as a function of the interaction between the body and the environment. The goal of our research was to provide a neuroanatomical examination of embodied cognition using action-related pictures and words. We used functional magnetic resonance imaging (fMRI) to examine whether there were shared and/or unique regions of activation between an ecologically valid semantic generation task and a motor task in the parietal-frontocentral network (PFN), as a function of stimulus format (pictures versus words) for two stimulus types (hand and foot). Unlike other methods for neuroimaging analyses involving subtractive logic or conjoint analyses, this method first isolates shared and unique regions of activation within-participants before generating an averaged map. The results demonstrated shared activation between the semantic generation and motor tasks, which was organized somatotopically in the PFN, as well as unique activation for the semantic generation tasks in proximity to the hand or foot motor cortex. We also found unique and shared regions of activation in the PFN as a function of stimulus format (pictures versus words). These results further elucidate embodied cognition in that they show that brain regions activated during actual motor movements were also activated when an individual verbally generates action-related semantic information. Disembodied cognition theories and limitations are also discussed.

Changes in functional magnetic resonance imaging cortical activation with cross education to an immobilized limb.

PURPOSE: The purpose of this study was to assess cortical activation associated with the cross-education effect to an immobilized limb, using functional magnetic resonance imaging. METHODS: Fourteen right-handed participants were assigned to two groups. One group (n = 7) wore a cast and strength trained the free arm (CAST-TRAIN). The second group (n = 7) wore a cast and did not strength train (CAST). Casts were applied to the nondominant (left) wrist and hand. Strength training was maximal isometric handgrip contractions (right hand) 5 d·wk(-1). Peak force (handgrip dynamometer), muscle thickness (ultrasound), EMG, and cortical activation (functional magnetic resonance imaging) were assessed before and after the intervention. RESULTS: CAST-TRAIN improved right handgrip strength by 10.7% (P < 0.01) with no change in muscle thickness. There was a significant group × time interaction for strength of the immobilized arm (P < 0.05). Handgrip strength of the immobilized arm of CAST-TRAIN was maintained, whereas the immobilized arm of CAST significantly decreased by 11% (P < 0.05). Muscle thickness of the immobilized arm decreased by an average of 3.3% (P < 0.05) for all participants and was not different between groups after adjusting for baseline differences. There was a significant group × time interaction for EMG activation (P < 0.05), where CAST-TRAIN showed an increasing trend and CAST showed a decreasing trend, pooled across arms. For the immobilized arm of CAST-TRAIN, there was a significant increase in contralateral motor cortex activation after training (P < 0.05). For the immobilized arm of CAST, there was no change in motor cortex activation. CONCLUSIONS: Handgrip strength training of the free limb attenuated strength loss during unilateral immobilization. The maintenance of strength in the immobilized limb via the cross-education effect may be associated with increased motor cortex activation.