Partial k-space reconstruction in single-shot diffusion-weighted echo-planar imaging.

Partial k-space sampling is frequently used in single-shot diffusion-weighted echo-planar imaging (DW-EPI) to reduce the TE and thereby improve the SNR. However, it increases the sensitivity of the technique to bulk rotational motion, which introduces a phase gradient across the tissue that shifts the echo in k-space. If the echo is displaced into the high spatial frequencies, conventional homodyne reconstruction fails, causing intensity oscillations across the image. Zero-padding, on the other hand, compromises the image resolution and may cause truncation artifacts. We present an adaptive version of the homodyne algorithm that detects the location of the echo in k-space and adjusts the center and width of the homodyne filters accordingly. The adaptive algorithm produces artifact-free images when the echo is shifted into the high positive k-space range, and reduces to the standard homodyne algorithm in the absence of bulk motion.     

MR monitoring of MR-guided radiofrequency thermal ablation of normal liver in an animal model

The purpose of this study was to determine the suitability of MRI to accurately detect radiofrequency (RF) thermoablative lesions created under MR guidance. In vivo RF lesions were created in the livers of six New Zealand White rabbits using a 2-mm-diameter titanium alloy RF electrode with a 20-mm exposed tip and a 50-W RF generator. This was performed using a 0.2T clinical C-arm MR imager for guidance and monitoring. Each animal was sacrificed and gross evaluation was performed. Histologic correlation was performed on the first two animals. The MR-compatible RF electrode was easily identified on rapid gradient-echo images used to guide electrode placement. A single lesion was created in each rabbit liver. Lesions ranged from approximately 10 to 17 mm in diameter (mean, 13.5 mm). T2-weighted and short T1 inversion recovery (STIR) images demonstrated lesions ranging in diameter from 12 to 18 mm (mean, 14.6 mm). Lesion dimensions determined from images closely correlated with those determined at gross examination with the discrepancy never exceeding 2 mm, for an r² value of .87. MRI performed at the time of MR-guided RF ablation accurately demonstrated created lesions. This modality may provide a new option for the treatment of local and regional neoplastic disease.     

Neurologic complications of reoperative and emergent abdominal aortic reconstruction

Patients undergoing emergent and reoperative abdominal aortic reconstructions are at increased risk for ischemic neurologic complications. Between 1986 and 1992 five patients sustained ischemic injuries to the spinal cord, nerve roots, or lumbosacral plexus. Four patients underwent reoperative aortic procedures including removal of an infected aortobifemoral graft and extra-anatomic bypass (n=3) and aortofemoral graft revision for primary graft failure (n=1). A fifth patient had a ruptured common iliac aneurysm repaired with an aortobifemoral graft. Three patients undergoing reoperative aortic procedures developed lower extremity paraparesis, patchy sensory deficits, and bowel and bladder dysfunction. Physical examination and electromyography localized the injury to the level of the cauda equina or lumbosacral plexus. The other patient in this group developed incomplete T12 paraplegia. Surgical reconstruction resulted in internal iliac exclusion in all four patients. The incidence of neurologic deficits during this study period was 18% (3/17) in patients requiring aortofemoral graft excision for infection. The patient undergoing aneurysm repair was noted to have paraplegia after surgery and died on the fourth postoperative day. Autopsy revealed evidence of multiple emboli to the kidneys, bowel, and spinal cord. Neurologic deficits after reoperative and emergent abdominal aortic reconstructions are uncommon but devastating complications. Of particular concern is the incidence of neurologic deficits after removal of aortofemoral grafts with disruption of collateral flow to the spinal cord and nerve roots. Consideration should be given to maintaining retrograde perfusion of at least one internal iliac artery via common femoral artery reconstruction in these patients.Presented at the Nineteenth Annual Meeting of the Peripheral Vascular Surgery Society, Seattle, Wash., June 5, 1994.     

Convulsive Therapy in the Treatment of Mania: McLean Hospital 1973-1986

The authors completed a retrospective chart review of the records of all patients identified with diagnoses of mania and schizoaffective disorder, manic type, who underwent electroconvulsive therapy between the years 1973 and 1986 at McLean Hospital. Ten of 18 manic patients (56%) and 3 of 9 schizoaffective patients (33%) experienced meaningful clinical benefit. The authors report the correlation of treatment and patient factors with outcome and review the literature on the convulsive therapy of mania.     

The TL MHC class Ib molecule has only marginal effects on the activation, survival and trafficking of mouse small intestinal intraepithelial lymphocytes

Thymus leukemia antigen (TL) is an MHC class Ib molecule that is highly conserved in rats and mice with no obvious human homolog. TL is expressed in mouse small intestinal epithelial cells and is known to interact with CD8alphaalpha homodimers, which are expressed by intraepithelial lymphocytes (IELs), some other T cell subsets and some non-T cells such as a subset of dendritic cells. We show here that TL is abundantly expressed on the basolateral surface of mouse small intestinal epithelial cells and that expression is abrogated in beta2m-/- mice but unaffected in TCR-/- mice or CD8alpha chain-/- mice. We demonstrate that the interaction between TL and CD8alphaalpha is not necessary for IEL survival in vitro or in vivo and does not modulate IEL trafficking in vivo. TL co-stimulation of alpha-CD3 antibody-activated IELs resulted in modestly enhanced production of IFN-gamma in one subset of IELs. The lack of effect on IEL survival and trafficking and the modest effect on IFN-gamma production suggest that the functional consequences of TL interaction with CD8alphaalpha as well as the more general biological role of TL in mucosal immunity remains to be discovered.