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Biomedical subjects

D M Healy

Publications and source records attributed to D M Healy.

9 recordsLinked to original sources
PubMed1998

Elastic image registration using correlations.

We have developed a multiscale algorithm for elastic registration of images. Rigid registration has many applications but it is often limited by distortions in the images. For example, different views of the same object produce distortions. Common examples of slightly different views producing a distortion can be found in medical imaging, such as matching a current mammogram or chest radiograph with one from a previous year, and in remote sensing, such as matching images taken from different satellite positions. We have developed two methods of elastic registration. Both are multiscale but one used an iterative minimization of the local error and the other uses a windowed correlation. We present preliminary results of the elastic registration method used on windowed correlations.

Algorithms↗
PubMed1998

Biodegradable controlled release glass in the repair of peripheral nerve injuries.

The experiments in this paper were concerned with the recovery of function and ease of application of an entubulation technique using a biodegradable, controlled release glass tube (CRG) for the repair of a transected peripheral nerve. The peroneal nerves of 15 New Zealand White rabbits were repaired with either a CRG tube filled with freeze-thawed muscle, or a conventional freeze thawed muscle graft (FTMG). These were compared with controls in which a CRG was used to enclose the cut ends of a nerve separated by a 1 cm gap. Electrophysiological and morphometric assessment was carried out 6 months after repair. No statistical difference was found in any test between the FTMG and the CRG tube filled with freeze thawed muscle. The CRG tube and 1 cm gap produced inferior levels of recovery of function when compared with the other two repair groups.

Action Potentials↗
PubMed1998

In vitro nerve repair--in vivo. The reconstruction of peripheral nerves by entubulation with biodegradeable glass tubes--a preliminary report.

Biodegradeable "controlled release" inorganic polymer glass tubes can be manufactured to fit the dimensions of any nerve and their rate of solubility can be adjusted to encompass the time taken for nerve regeneration. They have been used in a number of biological applications. The facial nerve was repaired in a group of five sheep by entubulation with biodegradeable glass tubes. The sheep were assessed 10 months after repair and compared with a similar sized group of normal sheep. It was found that while there was a reduction in the peak velocity of conduction in the repaired nerves and in the range of conduction velocities, the minimum conduction velocity was within normal limits. There was a diminution in all of the measured variables of nerve morphometry but in no case did this reach statistical significance. These findings are consistent with the view that regeneration of the nerves had taken place to a degree at least as effective as that seen in nerves of a similar size repaired by conventional means.

Animals↗
PubMed1998

Multiresolution elastic image registration.

We have developed a multiscale algorithm for elastic (or molded) alignment of images. There is a wide array of medical applications of elastic (as opposed to strictly rigid) alignment: Subtraction of previous images from current ones to identify changes is perhaps the most obvious. We present preliminary results of this molding technique on a variety of images, and conclude with some closing remarks about this and future directions and goals of this work.

Algorithms↗
PubMed1992

Wavelet-encoded MR imaging.

Wavelet encoding is presented and compared to phase encoding. In wavelet encoding a distribution of spins is excited by a slice selective RF pulse; for each repetition time the distribution excited has the profile of a wavelet at different scale and translation. The spin density can be reconstructed with an inverse wavelet transform. Wavelet encoding has three advantages over phase encoding: (1) there is no Gibb's ringing from partial volume effects, (2) the effective repetition time can be 36 times the repetition time for a 256 x 256 image, and (3) motion artifacts are local and dramatically reduced. Using wavelet encoding, a 256 x 256 T2-weighted projection image can be acquired in 33 s.

Artifacts↗
PubMed1991

Filtering noise from images with wavelet transforms.

A new method of filtering MR images is presented that uses wavelet transforms instead of Fourier transforms. The new filtering method does not reduce the sharpness of edges. However, the new method does eliminate any small structures that are similar in size to the noise eliminated. There are many possible extensions of the filter.

Artifacts↗
PubMed1991

Prophylactic minitracheotomy in lung resections. A randomized controlled study.

Thirty consecutive patients undergoing lung resections were randomized into two groups: Group A (n = 15) received minitracheotomy postoperatively and group B (n = 15) were control patients. Postoperative respiratory course was monitored by serial clinical assessments, chest x-ray examination, arterial blood gases, sputa bacterial cultures, and the patient's requirement and response to chest physiotherpy. The two groups were similarly matched in age (mean 58.5 years), smoking habits, pulmonary functions, and surgical procedures. Postoperative pulmonary complications of collapse/consolidation developed in 11 patients (two in group A and nine in group B) (p less than 0.03). Four patients (all in group B) required nimitracheotomy in addition to antibiotics and chest physiotherapy to treat their pneumonia. Chest physiotherapy requirement was less in group A than in group B, with a mean number of sessions of seven in group A and eight in group B and a mean total time of 92 minutes in group A and 112 minutes in group B. The mean duration of minitracheotomy was 4.13 days. Minor temporary symptoms resulted from the minitracheotomy in eight patients (42%) and included discomfort, voice changes, subcutaneous emphysema, and stridor. There was one case of long-term morbidity (5%)-skin scarring from wound infection at the site of the minitracheotomy. No postoperative deaths resulted. We conclude that the prophylactic use of minitracheotomy is safe and effective in decreasing postoperative respiratory complications in patients undergoing lung resections.

Adult↗
PubMedDate not supplied

Two applications of wavelets and related techniques in medical imaging.

We present two applications of wavelet and related techniques to problems arising in medical imaging. Both make considerable use of the edge detection and classification properties of wavelet-type representations. First we describe simple and effective techniques for image denoising and contrast enhancement based on the multiscale edge representation of images. These techniques are sufficiently flexible to successfully address the varying requirements posed by several different medical imaging modalities in common use today. Experimental results are presented to illustrate the application of these techniques to various types of medical images. Next we describe adapted waveform encoding, a technique for magnetic resonance imaging. One advantage of this technique is that it can be used to efficiently encode edge features of the object being imaged. This has a particular diagnostic application in tracking heart wall thickness during the cardiac cycle, which we present along with some experimental results along this line. We also present an analysis of the signal-to-noise ratios of images formed with this technique, as this is a factor of paramount importance in MRI. The fact that wavelet schemes tend to concentrate energy near edge features makes the result rather different than that found in standard Fourier based approaches. We indicate an exciting potential application of our technique: reducing spectral leakage in phosphorus spectroscopy.

Algorithms↗