Biomedical subjects

S D Wolff

Publications and source records attributed to S D Wolff.

28 records · Page 2Linked to original sources

PubMed1990

Sodium-23 nuclear magnetic resonance imaging of the rabbit kidney in vivo.

The mechanism by which the mammalian kidney generates a concentration gradient of sodium from cortex to papilla is still not entirely understood. Studies of how the kidney as an organ generates this gradient have been hampered by the lack of a noninvasive method for monitoring the intrarenal sodium distribution. Herein, we demonstrate the value of sodium-23 nuclear magnetic resonance (23Na-NMR) imaging to nondestructively assess the intrarenal sodium distribution. 23Na-NMR images were obtained from a surgically exposed kidney preparation that showed the two-dimensional distribution of sodium in the rabbit kidney. In the antidiuretic kidney this gradient resulted in papillary sodium concentrations that were approximately threefold higher than cortical values. Serial 23Na-NMR images obtained during saline infusion demonstrated the kinetics by which the sodium gradient increases with diuresis. The half-time for 23Na washout of the medulla of the kidney was approximately 6 min with this protocol. In addition, a three-dimensional data set of the sodium distribution of the kidney was obtained with voxel dimensions of 1.5 mm3 by use of a three-dimensional 23Na-NMR imaging technique. Without surgical exposure, 23Na-NMR images of the rabbit kidney were collected under completely noninvasive conditions by use of a surface coil. The 23Na-NMR signal from the kidney was easily detected; however, to obtain images of comparable signal-to-noise ratio to the surgically exposed kidney, spatial and temporal resolution were significantly reduced.

Animals↗

PubMed1989

Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo.

In this study the exchange between 1H magnetization in "free" water (1Hf) and that in a pool with restricted motion (1Hr) was observed in tissues in vivo using NMR saturation transfer methods. Exchange between these two pools was demonstrated by a decrease in the steady-state magnetization and relaxation times of 1Hf with radiofrequency irradiation of 1Hr. The pseudo-first-order rate constant for the movement of magnetization from 1Hf to 1Hr was approximately 1 s-1 in kidney and approximately 3 s-1 in skeletal muscle in vivo. Proton NMR imaging demonstrated that this exchange was tissue specific and generated a novel form of NMR image contrast. The extent of exchange between 1Hf and 1Hr as well as the topological correlation of the exchange with relaxation weighted images suggests that this pathway is a major determinant of the observed relaxation properties of water 1H in vivo.

Animals↗

PubMed1989

A simple HPLC method for quantitating major organic solutes of renal medulla.

A simple high performance liquid chromatography (HPLC) method of separating and quantitating the predominant organic solutes of the renal medulla is described. These organic solutes include myo-inositol, glycerophosphorylcholine, sorbitol, betaine, and urea. Other physiologically significant solutes, including glucose and mannitol, can be separated and quantitated concurrently with this method. With the use of this technique, the organic solutes of the rabbit kidney were determined. No new organic compounds were detected by HPLC that could significantly contribute to intracellular osmolality of the medulla. The values for the organic solutes already described were similar to those obtained by more complicated and limited approaches such as classical enzymatic techniques, ion electrodes, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectroscopy.

Animals↗

PubMed1989

Acute regulation of the predominant organic solutes of the rabbit renal inner medulla.

High concentrations of organic solutes are present in the medulla of the antidiuretic kidney. However, their role in and response to acute changes in the diuretic state are unknown. In this study the organic solute content of the renal medulla was determined from extracts with the use of high-performance liquid chromatography following the acute dilution of the medullary interstitium during various forms of diuresis. After acute infusion of saline and furosemide, inner medullary urea, sodium, inositol, sorbitol, and betaine decrease significantly with no change in glycerophosphorylcholine (GPC) content. After diuresis, inner medullary urea and sodium contents eventually returned to control levels, although inositol, sorbitol, and betaine contents still remained low. Addition of antidiuretic hormone to the saline/furosemide infusion gave similar results. In contrast, induction of diuresis from mannitol infusion caused an acute decrease in all 4 organic solutes, whereas glucose infusion caused an acute decrease in all organic solutes except sorbitol. These data demonstrate that a decrease in all four organic solutes can accompany medullary dilution. However, GPC and sorbitol do not decrease when diuresis is induced by furosemide or glucose, respectively. In addition, the recovery of these compounds in a normally functioning kidney after diuresis is much slower than the regeneration of the sodium chloride and urea gradients.

Animals↗

PubMed1988

NMR studies of renal phosphate metabolites in vivo: effects of hydration and dehydration.

The present study characterizes the 31P-nuclear magnetic resonance (NMR) spectrum of rabbit kidneys in vivo and evaluates the effect of hydration on phosphorous metabolites including the organic solute glycerophosphorylcholine (GPC). Cortical phosphorylethanolamine is the predominant component of the phosphomonoester region of the 31P spectrum. The contribution of blood to the spectrum is mainly from 2,3 diphosphoglycerate, which comprises approximately 30% of the inorganic phosphate region. Acute infusion of 0.9% saline decreases the sodium content of the inner medulla by greater than 50% in 15 min as shown by 23Na imaging. Despite this medullary Na dilution, no change in renal GPC content was observed for greater than 1 h even with the addition of furosemide (2.5 mg/kg) or furosemide and antidiuretic hormone (0.125 U/kg). However, 20 h of chronic hydration with 0.45% saline did result in a 30% decrease in renal GPC content when compared with dehydrated animals. These findings are consistent with GPC not playing a role in the short-term regulation of the medullary intracellular milieu in response to acute reductions in medullary Na content.

2,3-Diphosphoglycerate↗

PubMedDate not supplied

The effect of off-resonance radiofrequency pulse saturation on fMRI contrast.

This paper describes the use of off-resonance saturation to further manipulate the blood oxygenation level dependent (BOLD) contrast of fMRI. A customized narrow bandwidth radiofrequency pulse, applied with a range of frequency offsets prior to selection of each slice, was designed and incorporated into a gradient echo EPI sequence. This application takes advantage of the resonance frequency and linewidth differences between the oxygenated and deoxygenated state of blood in human brain during task activation and rest, and is capable of creating an enhancement in the contrast of the BOLD effect. Because of a possible contribution to the signal change from cerebro-spinal fluid, which has a much narrower linewidth and smaller frequency shift compared with the brain tissue, data were also collected using a nulling inversion pulse. The inversion pulse was applied before the off-resonance pulse and data acquisition to eliminate the CSF signal. Functional areas are thus more localized to the brain tissue.

Brain↗

PubMedDate not supplied

Using cardiac phase to order reconstruction (CAPTOR): a method to improve diastolic images.

A method is proposed to reconstruct multiphase images that accurately depicts the entire cardiac cycle. A segmented, gradient-recalled-echo sequence (FASTCARD) was modified to acquire data continuously. Images were reconstructed retrospectively by selecting views from each heartbeat based on cardiac phase rather than the time elapsed from the QRS complex. Cardiac phase was calculated using a model that compensates for beat-to-beat heart rate changes. Images collected using cardiac phase to order reconstruction (CAPTOR) depict the entire cardiac cycle and lack the temporal gap that is characteristic of prospectively reconstructed sequences. Time-volume curves of the left ventricle capture the contribution of atrial contraction to end-diastolic volume (EDV). Transmitral phase-contrast flow measurements show a second peak inflow (alpha wave) that is absent in the standard sequence. Because atrial contraction contributes to ventricular EDV, images using CAPTOR potentially may provide a more reliable measure of EDV, stroke volume, and ejection fraction than standard techniques.

Cardiac Volume↗

PubMedDate not supplied

Centric ordering is superior to gradient moment nulling for motion artifact reduction in EPI.

Echo-planar imaging (EPI) is sensitive to motion despite its rapid data acquisition rate. Compared with traditional imaging techniques, it is more sensitive to motion or flow in the phase-encode direction, which can cause image artifacts such as ghosting, misregistration, and loss of spatial resolution. Consequently, EPI of dynamic structures (eg, the cardiovascular system) could benefit from methods that eliminate these artifacts. In this paper, two methods of artifact reduction for motion in the phase-encode direction are evaluated. First, the k-space trajectory is evaluated by comparing centric with top-down ordered sequences. Next, velocity gradient moment nulling (GMN) of the phase-encode direction is evaluated for each trajectory. Computer simulations and experiments in flow phantoms and rabbits in vivo show that uncompensated centric ordering produces the highest image quality. This is probably due to a shorter readout duration, which reduces T2* relaxation losses and off-resonance effects, and to the linear geometry of phantoms and vessels, which can obscure centric blurring artifacts.

Animals↗

PubMedDate not supplied

Reduction of field of view in MRI using a surface-spoiling local gradient insert.

Herein is presented a method for suppressing the magnetic resonance signal to a controlled depth by applying a spatially heterogeneous spoiler field between the slice-select and readout pulses. Eliminating the signal from near-surface regions allows one to shrink the field of view without introducing aliasing artifacts, thereby decreasing imaging time over a smaller defined volume. A unique planar magnetic gradient coil was constructed to generate the spoiler field. Phantom and human subject studies showed that the signal can be suppressed to controlled distances of up to 90 mm from the coil, with modest requirements on power supplies, pulse sequences, and materials, and with no increase in imaging time.

Artifacts↗

PubMedDate not supplied

Thoracic Kaposi sarcoma in AIDS: CT findings.

Cases of acquired immunodeficiency syndrome (AIDS) related Kaposi sarcoma (KS) were reviewed to characterize the spectrum of thoracic findings seen with chest CT. Of 15 patients with AIDs-related KS involving the chest, 13 (87%) demonstrated pulmonary parenchymal disease characterized by multiple, bilateral flame-shaped or nodular lesions with ill-defined margins distributed along bronchovascular bundles. Pleural disease was noted in 10 (67%) patients, characterized by 9 cases of pleural effusions and 1 case of pleural implants. Chest wall disease involving the sternum, ribs, thoracic spine, and/or subcutaneous tissue was noted in eight (53%) patients. Although pleural and parenchymal lung disease are recognized manifestations of thoracic KS, there is also a high incidence of extrapulmonary chest disease evident on CT in patients with AIDS.

AIDS-Related Opportunistic Infections↗