Andrzej Jesmanowicz

Functional magnetic resonance imaging of complex human movements

Functional magnetic resonance imaging (FMRI) is a new, noninvasive imaging tool thought to measure changes related to regional cerebral blood flow (rCBF). Previous FMRI studies have demonstrated functional changes within the primary cerebral cortex in response to simple activation tasks, but it is unknown whether FMRI can also detect changes within the nonprimary cortex in response to complex mental activities. We therefore scanned six right-handed healthy subjects while they performed self-paced simple and complex finger movements with the right and left hands. Some subjects also performed the tasks at a fixed rate (2 Hz) or imagined performing the complex task. Functional changes occurred (1) in the contralateral primary motor cortex during simple, self-paced movements; (2) in the contralateral (and occasionally ipsilateral) primary motor cortex, the supplementary motor area (SMA), the premotor cortex of both hemispheres, and the contralateral somatosensory cortex during complex, self-paced movements; (3) with less intensity during paced movements, presumably due to the slower movement rates associated with the paced (relative to self-paced) condition; and (4) in the SMA and, to a lesser degree, the premotor cortex during imagined complex movements. These preliminary results are consistent with hierarchical models of voluntary motor control.

Real-time 3D image registration for functional MRI

Subject head movements are one of the main practical difficulties with brain functional MRI. A fast, accurate method for rotating and shifting a three‐dimensional (3D) image using a shear factorization of the rotation matrix is described. Combined with gradient descent (repeated linearization) on a least squares objective function, 3D image realignment for small movements can be computed as rapidly as whole brain images can be acquired on current scanners. Magn Reson Med 42:1014–1018, 1999.

High-resolution fMRI using multislice partial k-space GR-EPI with cubic voxels

The premises of this work are: 1) the limit of spatial resolution in fMRI is determined by anatomy of the microcirculation; 2) because of cortical gray matter tortuosity, fMRI experiments should (in principle) be carried out using cubic voxels; and 3) the noise in fMRI experiments is dominated by low‐frequency BOLD fluctuations that are a consequence of spontaneous neuronal events and are pixel‐wise dependent. A new model is proposed for fMRI contrast which predicts that the contrast‐to‐noise ratio (CNR) tends to be independent of voxel dimensions (in the absence of partial voluming of activated tissue), TE, and scanner bandwidth. These predictions have been tested at 3 T, and results support the model. Scatter plots of fMRI signal intensities and low‐frequency fluctuations for activated pixels in a finger‐tapping paradigm demonstrated a linear relationship between signal and noise that was independent of TE. The R2 value was about 0.9 across eight subjects studied. The CNR tended to be constant across pixels within a subject but varied across subjects: CNR = 3.2 ± 1.0. fMRI statistics at 20‐ and 40‐ms TE values were indistinguishable, and TE values as short as 10 ms were used successfully. Robust fMRI data were obtained across all subjects using 1 × 1 × 1 mm3 cubic voxels with 10 contiguous slices, although 1.5 × 1.5 × 1.5 mm3 was found to be optimum. Magn Reson Med 46:114–125, 2001.

Identification and characterization of cerebral cortical response to esophageal mucosal acid exposure and distention.

BACKGROUND & AIMS Esophageal acid exposure is a common occurrence in healthy individuals and patients with esophagitis. Clinically, perception of this exposure ranges from no perception to severe heartburn and chest pain. Cerebral cortical response to esophageal mucosal contact to acid has not been systematically studied. The aim of this study was to elucidate cerebral cortical response to esophageal acid exposure in normal individuals by functional magnetic resonance imaging (FMRI). METHODS We studied 10 normal healthy volunteers. Cortical FMRI response to 10 minutes of intraesophageal perfusion of 0.1N HCl (1 mL/min) was determined, and the results were compared with those of saline infusion and balloon distention. RESULTS Acid perfusion did not induce heartburn or chest pain but increased FMRI signal intensity by 6.7% +/- 2.0% over the preperfusion values. No increase was detected for saline infusion. FMRI signal intensity to balloon distention was similar to that of acid perfusion. Activation latency, activation to peak, and the deactivation periods for response to acid perfusion were significantly longer than those of balloon distention (P < 0.05). CONCLUSIONS Contact of esophageal mucosa with acid, before inducing heartburn, evokes a cerebral cortical response detectable by FMRI. Temporal characteristics of this response are significantly different from those induced by esophageal balloon distention.

Functional magnetic resonance imaging in partial epilepsy.

Summary: Functional magnetic resonance imaging (FMRI) detects signal changes in brain that accompany regional changes in neuronal activity. In normal human brain, FMRI shows changes in signal in the postcentral gyrus or superior temporal gyrus that correlate with voluntary motor activity or language processing, respectively. The model used to explain the changes in signal linked temporally with cerebral activity is a reduction in cerebral capillary deoxyhemoglobin concentration due to the increased blood flow that accompanies neuronal activity in the cerebrum. FMRI has been used in normal subjects but not extensively in patients. To determine the feasibility of using FMRI to map cerebral functions in patients with partial epilepsy syndromes, we performed a pilot study, using FMRI to identify signal changes in motor and language areas in response to tasks that activate those areas. Signal changes in epilepsy patients approximated those observed in volunteers. We conclude that FMRI can be developed as a method for functional cerebral mapping in partial epilepsies.

Single-shot magnetic field mapping embedded in echo-planar time-course imaging

A technique for acquiring magnetic field maps simultaneously with gradient‐recalled echo‐planar time‐course data is described. This technique uses a trajectory in which the central part of k‐space is collected twice. For a 64 × 64 image acquired with a 125‐kHz bandwidth, a field map suitable for geometric correction can be collected simultaneously with the echo‐planar time‐course data in <70 ms. The field maps generated by this technique are registered with the magnitude images because they are calculated using the same data. They do not suffer from errors due to subject motion, or from different geometric distortions that can result from using different pulse sequences. In addition to correcting geometric distortions that resulted from dynamic magnetic field perturbations, this method was used to measure field shifts arising from respiration and jaw motion across five subjects. Values ranged from 0.035 to 0.165 parts per million (ppm). Magn Reson Med 50:839–843, 2003.

Inductive (flux linkage) coupling to local coils in magnetic resonance imaging and spectroscopy

Abstract An engineering analysis of inductive (flux linkage) coupling to local coils used for NMR imaging and spectroscopy is presented. It is emphasized that the concept of “resonance” must be carefully defined because of complexity introduced into the equivalent circuit by the coupling loop inductance and the mutual inductance between the coupling and receiving loops. The condition of match to the transmission line is unique and coincides with the maximum in receiver voltage. The effect of matching on frequency detuning is analyzed, and it is shown that the coupling loop should be as small as possible and the coupling coefficient as large as possible. A convenient variable inductive coupler is described in which a variable capacitor is displaced on odd number of quarter wavelengths from the coupling loop. The variable coupler has been implemented using a voltage controlled tuning capacitor (varactor).

B0-fluctuation-induced temporal variation in EPI image series due to the disturbance of steady-state free precession

Steady‐state free precession (SSFP) can develop under a train of RF pulses, given the condition TR < T2. SSFP in multi‐shot imaging sequences has been well studied. It is shown here that serial single‐shot echo‐planar imaging (EPI) acquisition can also develop SSFP, and the SSFP can be disturbed by B0 fluctuation, causing voxel‐wise temporal variation. This SSFP disturbance is predominantly present in cerebrospinal fluid (CSF) regions due to the long T2 value. By applying a sufficiently strong crusher gradient in the EPI pulse sequence, the temporal variation induced by SSFP disturbance can be suppressed due to diffusion. Evidence is provided to indicate that physiological motions such as cardiac pulsation and respiration could affect the voxel‐wise time courses through the mechanism of SSFP disturbance. It is advised that if the disturbance is observed in serial EPI images, the crusher should be made stronger to eliminate the unwanted temporal variation. Magn Reson Med 44:758–765, 2000.

High resolution MR imaging of glomus tumor.

High resolution magnetic resonance images of a surgically confirmed glomus tumor of the finger obtained with a surface coil are shown. Magnetic resonance has the potential to preoperatively evaluate soft tissue tumors of these regions which are poorly imaged by other modalities.

Planar-pair local coils for high-resolution magnetic resonance imaging, particularly of the temporomandibular joint

The two-loop--one-gap loop--gap resonator (planar pair) has been investigated as a local receiving coil for high-resolution proton imaging at 1.5 T (63.8 MHz). Sensitivity contours were determined on the bench by measuring the voltage induced in the coil when it is placed on the surface of a tank containing 0.1-M NaCl, as a function of the coordinates and orientation of a radiating dipole inside the tank. Contours were obtained as a function of the diameter D of the two loops, and their separation d. For comparison, considerable data also were obtained for single-turn circular loops as a function of loop diameter. Coil quality factors, Qs, are reported in free space and the saline tank as a function of geometric parameters. Contours also were obtained using phantoms in a whole-body imager. Planar-pair coils couple to slabs of approximately (2D + d) X D cross section, and are superior to circular coils for imaging anatomic structures that are somewhat elongated. A particularly important feature of planar-pair local coils is that they are intrinsically isolated from the whole-body coil of the imager, and no special passive or active circuits are required when the whole-body coil is used for excitation. Planar-pair local coils have been optimized for imaging of the temporomandibular joint, and an image is shown.