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Biomedical subjects

E X Wu

Publications and source records attributed to E X Wu.

8 recordsLinked to original sources
PubMed1994

A new 3D localization technique using quadratic field gradients.

A new method of 3D spatial selection using pulsed quadratic field gradients is presented. Like previous pulsed quadratic gradient methods the new method requires only two RF pulses to achieve selection in three dimensions. Unlike previous methods, however, precise alignment of linear and quadratic gradient coils is not required. This characteristic allows the method to be used with small or surface quadratic gradient coils. The method is demonstrated on phantom and rats.

Image Processing, Computer-Assisted↗
PubMed1994

Experimental high-frequency ultrasound can detect graft rejection after small bowel transplantation.

Early diagnosis of graft rejection after small bowel transplantation (SBT) can allow prompt institution of vigorous immunosuppressive therapy, with resultant reversal of the rejection process. The current method for graft monitoring is random mucosal biopsy from a stomal site or through an endoscope. However, because early rejection often has a patchy distribution, it could be missed by random biopsy. We hypothesized that the pathological process of rejection would alter acoustic impedance of the tissue and thus change the ultrasonic patterns of the graft intestinal wall. If this hypothesis is correct, then high-frequency endoscopic ultrasound (US) could be used to monitor the entire transplanted bowel and guide the biopsy, with improved yields. This hypothesis was tested in a rat orthotopic SBT model. Sixty-two intestinal specimens (9 isografts, 12 allografts treated with cyclosporine A [CsA], 22 untreated allografts, and 19 intestines from normal rats) were collected for in vitro transluminal US imaging (30 MHz) and histopathologic study. The echo pattern of normal rat intestinal wall consisted of five echo layers that correlated spatially with the histological layers: the innermost hyperechoic layer 1, plus hypoechoic layer 2, corresponded to the mucosa; hyperechoic layer 3, the submucosa; anechoic layer 4, the muscularis propria; and hyperechoic layer 5, the serosa. The isografts and CsA-treated allografts were identical histologically and ultrasonically to normal intestine. However, the echo patterns of the untreated allografts had progressive loss of architectural stratification, with worsening rejection. The change began with patchy indistinctness and disruption of hyperechoic layers 1, 3 and 5, and progressed to total obliteration of the layers, with the intestinal wall becoming a nonstratified hypoechoic structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Self-correction of proton spectroscopic images for gradient eddy current distortions and static field inhomogeneities.

A postprocessing method of correcting for gradient eddy current distortions and inter-voxel static field inhomogeneity in spectroscopic imaging is presented. Data is acquired normally and all spatial processing is performed. The FID in each voxel is then digitally filtered to extract the signal from a single reference line. Phase multiplying the original FID by the phase of this reference signal corrects for gradient eddy currents and static field offsets. Computer simulations show that the method is robust with respect to noise, filter bandwidth and the presence of small lines close to the reference line. The method is demonstrated on proton spectroscopic images of phantoms.

Computer Simulation↗
PubMed1993

Sonographic and computed tomography characteristics of liver ablation lesions induced by high-intensity focussed ultrasound.

RATIONALE AND OBJECTIVES: The authors have previously demonstrated the ability of high-intensity focused ultrasound (HIFU) to extracorporeally induce selective tissue destruction in the liver without causing damage to the intervening abdominal wall. The potential usefulness of HIFU as a noninvasive therapy for liver cancer has been suggested. This study observes sonographic and computed tomography (CT) characteristics of HIFU-ablated liver tissue in an attempt to assess the possibility of using these imaging methods to monitor the therapeutic results. METHODS: A sonoablated lesion was induced in the liver in each of 20 rabbits with a HIFU therapeutic system. Sequential imaging of the hepatic sonolesions with sonography and CT was performed up to 8 days after treatment, and the imaging patterns were correlated with the histopathology. RESULTS: Hepatic sonoablated tissue could be clearly visualized by sonography as a hypoechoic lesion. On contrast-enhanced CT, the sonolesions were depicted as nonenhanced low-density regions. There was good correlation among the sizes of sonography- and CT-depicted lesions and pathologic specimens. CONCLUSION: In this model, sonography and contrast-enhanced CT were useful imaging modalities for monitoring sonolesion evolution after HIFU treatment.

Animals↗
PubMed1992

Phase-scrambled RF excitation for 3D volume-selective multislice NMR imaging.

An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume-selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice-encoded phase components along the slice-selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.

Algorithms↗
PubMed1992

Microscopic mechanism of attenuation of compressional ultrasonic waves in tissue-mimicking phantom materials.

An investigation was performed to determine whether the sound-attenuation-insuspensions theory of Allegra and Hawley can be used to explain the compressional (longitudinal wave) attenuation of ultrasonically tissue-mimicking materials commonly used in phantoms for testing the performance of medical ultrasound systems. These materials are composed of microscopic graphite particles suspended in a gel. The theory was first tested using materials containing spherical glass beads instead of graphite particles because these materials more closely fit the geometric conditions assumed in the theory. For the glass bead type materials as well as the graphite particle type materials, the attenuation coefficients predicted using the Allegra and Hawley model agreed rather well with experimental measurements over the diagnostic frequency range.

Biocompatible Materials↗