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Biomedical subjects

J D Hazle

Publications and source records attributed to J D Hazle.

At least 19 recordsLinked to original sources
PubMed2004

Technical developments for cerebral thermal treatment: water-cooled diffusing laser fibre tips and temperature-sensitive MRI using intersecting image planes.

The aim was to determine if water-cooled diffusing tips could produce larger and safer (better controlled) thermal lesions than non-cooled diffusing tips at 980 nm. Thermal lesions were induced in beef myocardium in vitro with and without water cooling using a 980 nm diode laser at various power levels. Seven intracerebral treatments were performed in six canines using water-cooled diffusing tips with four animals having intracerebral transmissible venereal tumours grown from inoculate. Magnetic resonance thermal imaging (MRTI)-based feedback software using a fast, radio frequency-spoiled gradient echo acquisition with two intersecting image planes was used for on-line monitoring and control of treatment and for the evaluation of in vivo laser lesion production. In cases where two-plane MRTI was employed, the maximum calculated temperature was compared in each plane. Using water-cooled tips and 400 micro m core diameter laser diffusing fibres in in vitro beef myocardium, power of up to 9.5 W was applied for 8 min without tip failure. Without cooling, tip failure occurred in under 4 min at 6 W, in under 2 min at 7 W and instantaneously at 8 W. Additionally, char accompanied lesions made with uncooled tips while cooled application resulted in only minimal char at only the highest thermal dose. Achieved lesion cross-sectional diameters in in vitro samples were up to 26.5 x 23.3 mm when water cooling was used. In canine brain and transmissible venereal tumours, up to 18.1 x 21.4 mm lesions were achieved. It is concluded that water cooling allows safe application of higher power to small core diameter diffusing tip fibres, which results in larger thermal lesions than can be achieved without cooling. Two-plane MRTI enhances on-line monitoring and feedback of thermal treatment.

Animals↗
PubMed2004

Transurethral ultrasound applicators with directional heating patterns for prostate thermal therapy: in vivo evaluation using magnetic resonance thermometry.

A catheter-based transurethral ultrasound applicator with angularly directional heating patterns has been designed for prostate thermal therapy and evaluated in canine prostate in vivo using MRI to monitor and assess performance. The ultrasound transducer array (3.5 mm diameter tubular transducers, 180 degrees active sectors, approximately 7.5 MHz) was integrated to a flexible delivery catheter (4 mm OD), and encapsulated within an expandable balloon (35 mm x 10 mm OD, 80 ml min(-1) ambient water) for coupling and cooling of the prostatic urethra. These devices were used to thermally coagulate targeted portions of the canine prostate (n = 2) while using MR thermal imaging (MRTI) to monitor the therapy. MRI was also used for target definition, positioning of the applicator, and evaluation of target viability post-therapy. MRTI was based upon the complex phase-difference mapping technique using an interleaved gradient echo-planar imaging sequence with lipid suppression. MRTI derived temperature distributions, thermal dose exposures, T1-contrast enhanced MR images, and histology of sectioned prostates were used to define destroyed tissue zones and characterize the three-dimensional heating patterns. The ultrasound applicators produced approximately 180 degrees directed zones of thermal coagulation within targeted tissue which extended 15-20 mm radially to the outer boundary of the prostate within 15 min. Transducer activation lengths of 17 mm and 24 mm produced contiguous zones of coagulation extending axially approximately 18 mm and approximately 25 mm from base to apex, respectively. Peak temperatures around 90 degrees C were measured, with approximately 50 degrees C-52 degrees C corresponding to outer boundary t43 = 240 min at approximately 15 min treatment time. These devices are MRI compatible, and when coupled with multiplanar MRTI provide a means for selectively controlling the length and sector angle of therapeutic thermal treatment in the prostate.

Animals↗
PubMed2003

Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance.

Metal nanoshells are a class of nanoparticles with tunable optical resonances. In this article, an application of this technology to thermal ablative therapy for cancer is described. By tuning the nanoshells to strongly absorb light in the near infrared, where optical transmission through tissue is optimal, a distribution of nanoshells at depth in tissue can be used to deliver a therapeutic dose of heat by using moderately low exposures of extracorporeally applied near-infrared (NIR) light. Human breast carcinoma cells incubated with nanoshells in vitro were found to have undergone photothermally induced morbidity on exposure to NIR light (820 nm, 35 W/cm2), as determined by using a fluorescent viability stain. Cells without nanoshells displayed no loss in viability after the same periods and conditions of NIR illumination. Likewise, in vivo studies under magnetic resonance guidance revealed that exposure to low doses of NIR light (820 nm, 4 W/cm2) in solid tumors treated with metal nanoshells reached average maximum temperatures capable of inducing irreversible tissue damage (DeltaT = 37.4 +/- 6.6 degrees C) within 4-6 min. Controls treated without nanoshells demonstrated significantly lower average temperatures on exposure to NIR light (DeltaT < 10 degrees C). These findings demonstrated good correlation with histological findings. Tissues heated above the thermal damage threshold displayed coagulation, cell shrinkage, and loss of nuclear staining, which are indicators of irreversible thermal damage. Control tissues appeared undamaged.

Animals↗
PubMed2000

Monitoring of high-intensity focused ultrasound-induced temperature changes in vitro using an interleaved spiral acquisition.

An interleaved, spoiled gradient-echo spiral acquisition technique was implemented to monitor high-intensity focused ultrasound heating of porcine kidney ex vivo by measuring temperature induced phase shifts in the detected MR signal. Echo time, flip angle, repetition time, number of interleaves, and readout time were varied to observes effects on temperature sensitivity and phase-difference noise. The temperature response of the interleaved spiral acquisition was found to be comparable to a spoiled fast gradient-echo sequence of comparable in-plane spatial resolution. However, when imaging with an optimal echo time, spiral acquisition offers dramatically increased temporal resolution for comparable spatial resolution. Magn Reson Med 43:909-912, 2000.

Animals↗
PubMed2000

Performance analysis of a new semiorthogonal spline wavelet compression algorithm for tonal medical images.

Lossy image compression is thought to be a necessity as radiology moves toward a filmless environment. Compression algorithms based on the discrete cosine transform (DCT) are limited due to the infinite support of the cosine basis function. Wavelets, basis functions that have compact or nearly compact support, are mathematically better suited for decorrelating medical image data. A lossy compression algorithm based on semiorthogonal cubic spline wavelets has been implemented and tested on six different image modalities (magnetic resonance, x-ray computed tomography, single photon emission tomography, digital fluoroscopy, computed radiography, and ultrasound). The fidelity of the reconstructed wavelet images was compared to images compressed with a DCT algorithm for compression ratios of up to 40:1. The wavelet algorithm was found to have generally lower average error metrics and higher peak-signal-to-noise ratios than the DCT algorithm.

Algorithms↗
PubMed1999

The feasibility of elastographic visualization of HIFU-induced thermal lesions in soft tissues. Image-guided high-intensity focused ultrasound.

The potential for visualizing high-intensity focused ultrasound (HIFU)-induced thermal lesions in biological soft tissues in vitro using elastography was investigated. Thermal lesions were created in rabbit paraspinal skeletal muscle in vivo. The rabbits were sacrificed 60 h following the treatment and lesioned tissues were excised. The tissues were cast in a block of clear gel and elastographic images of the lesions were acquired. Gross pathology of the tissue samples confirmed the characteristics of the lesions.

Animals↗
PubMed1999

Elastographic characterization of HIFU-induced lesions in canine livers.

The elastographic visualization and evaluation of high-intensity focused ultrasound (HIFU)-induced lesions were investigated. The lesions were induced in vitro in freshly excised canine livers. The use of different treatment intensity levels and exposure times resulted in lesions of different sizes. Each lesion was clearly depicted by the corresponding elastogram as being an area harder than the background. The strain contrast of the lesion/background was found to be dependent on the level of energy deposition. A lesion/background strain contrast between -2.5 dB and -3.5 dB was found to completely define the entire zone of tissue damage. The area of tissue damage was automatically estimated from the elastograms by evaluating the number of pixels enclosed inside the isointensity contour lines corresponding to a strain contrast of -2.5, -3 and -3.5 dB. The area of the lesion was measured from a tissue photograph obtained at approximately the same plane where elastographic data were collected. The estimated lesion areas ranged between approximately 10 mm2 and 110 mm2. A high correlation between the damaged areas as depicted by the elastograms and the corresponding areas as measured from the gross pathology photographs was found (r2 = 0.93, p value < 0.0004, n = 16). This statistically significant high correlation demonstrates that elastography has the potential to become a reliable and accurate modality for HIFU therapy monitoring.

Animals↗
PubMed1998

Elastographic imaging of thermal lesions in soft tissue: a preliminary study in vitro.

The use of elastography for the visualization of thermal lesions in biological soft tissue in vitro was investigated. Thermal lesions were created in samples of postmortem ovine kidney using a surgical neodymium: YAG (Nd:YAG) laser. The kidney samples were cast in gel, and elastographic images of the lesions were constructed using sonographic information and external markers to locate the region of interest. Gross pathology of the kidney samples confirmed the dimensions of the lesions. Good correlation between the lesion length along the laser fiber axis and maximum diameter measured off of the fiber axis determined from elastographic images and gross pathology photographs was found.

Animals↗
PubMed1998

Evaluation of helical computed tomography scan parameters for vascular imaging.

Helical x-ray computed tomography (hCT) is the volume acquisition of image data in which the data set represents a series of projections obtained in a helical spatial distribution. Data acquisition times and spatial resolution are determined largely by two user defined parameters--collimation and pitch. Each combination of pitch and collimation results in a slice profile which can be considered as the apparent slice thickness. Careful selection of pitch and collimation allows the acquisition of up to 20 cm of axial data in a breathold or first pass of bolus contrast material. This makes helical CT an excellent technique for angiographic (CTA) studies. Additionally, slices can be reconstructed at any interval to reduce partial volume averaging, minimizing the beading artifacts seen in maximum intensity projections (MIP) when interslice resolution is poor. We have evaluated a range of collimation and pitches for clinical CTA. Additionally, three reconstruction filters were included to determine the optimal frequency (spatial) properties for these techniques. Objective and subjective analyses were performed. We found pitches of up to 1.5:1 to be acceptable for all collimations. For a given scan length (z direction), selection of thinner collimation and higher pitch resulted in better SNR and observer scoring for angiographic presentations.

Angiography↗
PubMed1998

Correlation between dynamic MRI and outcome in patients with malignant gliomas.

We assessed the correlation between dynamic MRI results and clinical outcomes in patients with malignant gliomas. Rapid serial MRIs were obtained after bolus injection of gadolinium that resulted in an initial fast uptake followed by a slow uptake of contrast. The maximum rate of uptake and delayed rate of uptake were correlated with survival and prognostic covariates such as age and histology. In 121 subjects, higher maximum uptake rates, 3.6 signal intensity units per second or greater, were associated with shorter survival (p = 0.0066). The correlation of delayed rate of uptake with survival was less significant. After adjusting for age, histology, and Karnofsky performance score, the maximum rate of uptake remained more significantly correlated with survival than the delayed rate of uptake. Thirty-one patients had surgery within 1 month of dynamic MRI, and those with glioblastoma multiforme or anaplastic gliomas had higher maximum rates of uptake than those with pure necrosis or mixed tumor and necrosis (p = 0.022). No correlation between delayed rate of uptake and histology was seen in this group of patients. Our results suggest that the maximum rate of uptake in dynamic MRI can be a prognostic measure for patients with malignant gliomas. Further prospective study is needed to assess the utility of this technique for evaluating brain tumors.

Adolescent↗
PubMed1997

Magnetic resonance imaging of the central nervous system of the rhesus monkey.

The purpose of the study reported here was to document the ability of magnetic resonance imaging to depict the imaging characteristics of normal structures within the central nervous system of adult rhesus monkeys. The head and the cervical and thoracic parts of the spinal cord of two rhesus monkeys were imaged in a clinical 1.5-T whole-body imager. Specific images were selected, and some notable structures were identified. Results of this study document the usefulness of MRI as an expeditious, noninvasive research and diagnostic imaging technique and illustrates the normal magnetic resonance signal patterns of the brain and spinal cord in rhesus monkeys.

Animals↗
PubMed1996

Glioblastoma multiforme arising in the irradiated spinal cord of a rhesus monkey (Macaca mulatta).

An adult female rhesus monkey that had received 44.0 Gy of cobalt 60 radiation to 8 cm of the cervical and upper thoracic spinal cord approximately 2.8 years postirradiation developed a sudden onset of self-mutilation and loss of function of the right arm followed progressively by loss of function of the left arm and terminally bilateral paresis of the legs. Histopathologic examination of the cervical spinal cord revealed a glioblastoma multiforme that extended from the cervical medullary junction to the sixth cervical vertebrae. Because of the infrequent occurrence of spontaneous neoplasia in rhesus monkeys and the location in the radiation field, the glioblastoma is believed to be radiation induced.

Animals↗
PubMed1995

Intraoperative electron beam radiation therapy: technique, dosimetry, and dose specification: report of task force 48 of the Radiation Therapy Committee, American Association of Physicists in Medicine.

Intraoperative radiation therapy (IORT) is a treatment modality whereby a large single dose of radiation is delivered to a surgically open, exposed cancer site. Typically, a beam of megavoltage electrons is directed at an exposed tumor or tumor bed through a specially designed applicator system. In the last few years, IORT facilities have proliferated around the world. The IORT technique and the applicator systems used at these facilities vary greatly in sophistication and design philosophy. The IORT beam characteristics vary for different designs of applicator systems. It is necessary to document the existing techniques of IORT, to detail the dosimetry data required for accurate delivery of the prescribed dose, and to have a uniform method of dose specification for cooperative clinical trials. The specific charge to the task group includes the following: (a) identify the multidisciplinary IORT team, (b) outline special considerations that must be addressed by an IORT program, (c) review currently available IORT techniques, (d) describe dosimetric measurements necessary for accurate delivery of prescribed dose, (e) describe dosimetric measurements necessary in documenting doses to the surrounding normal tissues, (f) recommend quality assurance procedures for IORT, (g) review methods of treatment documentation and verification, and (h) recommend methods of dose specification and recording for cooperative clinical trials.

Combined Modality Therapy↗
PubMed1994

Dosimetry characteristics of four fast neutron generators involved in RTOG interinstitutional clinical trials.

PURPOSE: To demonstrate the consistency of dosimetry data used for four fast neutron generators involved in inter-institutional clinical trials. METHODS AND MATERIALS: Central-axis dosimetry characteristics (field size dependence, percentage depth dose, beam modifier factors) at four institutions were measured by independent physicists from the Radiological Physics Center. These measurements were made in water with a single set of dosimetry equipment using tissue equivalent ionization chambers. Measurements were made with the chamber cavities filled with stationary air and flowing tissue-equivalent gas. All measurements were performed using techniques developed by the Radiological Physics Center for conventional radiotherapy equipment. The results of our measurements were compared to the data used by the institution to determine the consistency of patient doses reported to the Radiation Therapy Oncology Group. RESULTS: The agreement of the Radiological Physics Center and institution data is similar to what is typically found with conventional radiotherapy equipment. CONCLUSIONS: The doses reported by these institutions to the Fast Neutron Working Group of the Radiation Therapy Oncology Group are consistent, within accepted clinical criteria.

Fast Neutrons↗
PubMed1992

Quality assurance for intraoperative electron radiotherapy clinical trials: ionization chamber and mailable thermoluminescent dosimeter results.

Ionization chamber and thermoluminescent dosimeter measurements were made to verify the dosimetry data provided to the Radiation Therapy Chart Review office of interinstitutional electron intraoperative radiotherapy clinical trials. The ionization measurements included intraoperative radiotherapy applicator output and depth dose measurements made at the stated 80% and 50% depths at 14 different radiotherapy facilities. Mailable thermoluminescent dosimeter measurements, including output and depth dose measurements were made at 16 institutions. The mailable thermoluminescent dosimeter results show similar inter-institutional agreement, both for output and depth dose comparison, with the corresponding ion chamber results for intraoperative radiotherapy applicators. These results are compared to similar measurements made for conventional electron applicators.

Clinical Trials as Topic↗