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Biomedical subjects

M J Bronskill

Publications and source records attributed to M J Bronskill.

15 recordsLinked to original sources
PubMed1992

Quantitative magnetic resonance imaging parameters and their relationship to mammographic pattern.

BACKGROUND: Breast cancer exhibits wide international variation in incidence, which has led to the identification of several factors correlating with the risk of the disease. Magnetic resonance imaging (MRI) techniques can provide quantitative information about the biological and physical properties of tissue. PURPOSE: This work tested several magnetic resonance tissue parameters for their ability to distinguish quantitatively between breast tissues in subjects at substantially different risk for breast cancer as defined indirectly by their parenchymal pattern on mammograms. METHODS: Quantitative MRI parameters (relative water content, longitudinal relaxation time [T1], and transverse relaxation time [T2]) were measured for breast tissue using newly developed techniques in two groups of women with mammographic parenchymal appearance associated with high (Dy pattern [i.e., extensive nodular or diffuse density]; n = 12) or low (N1 pattern [i.e., breast containing mainly fat]; n = 11) risk of breast cancer. RESULTS: The two groups have significantly different average relative water content (P less than .0001) and average T1 (P less than .0001). Pixel histograms of T2 values show marked differences between the two groups which can be characterized with a fourth moment parameter. CONCLUSIONS: Quantitative MRI techniques exhibit good potential for assessing tissue characteristics in the breast that are associated with risk of breast cancer. IMPLICATIONS: Future work will address the direct correlation of MRI parameters with risk of breast cancer.

Adult↗
PubMed1991

Optimization of prostatic magnetic resonance imaging technique.

With a 1.5-T magnetic resonance imager the authors systematically varied a large number of technical factors to obtain an optimum balance between high image quality and reasonable imaging time for the prostate gland. Each parameter was adjusted relative to benchmark images of very high quality to achieve a reasonable acquisition time with as little loss of the signal-to-noise ratio (SNR) as possible. Image quality was judged subjectively by magnetic resonance radiologists and objectively by measurements of SNR for the prostate. The authors recommend multislice, multiecho spin-echo pulse sequences with dual surface coils, fat suppression, reduced bandwidth, a repetition time of 1500 ms, echo times of 30 and 60 ms, a flip angle of 60 degrees, two excitations, a slice thickness of 5 mm with a 1.5-mm gap and 192 phase-encoding steps. The acquisition time for one such series was 9.6 minutes.

Humans↗
PubMed1990

Optimization of survey protocols for MRI.

A method for evaluating the sensitivity of MRI protocols to changes in an arbitrary number of tissue parameters over a broad range of parameter values is presented. This analysis is useful for choosing an optimal basis set of images for either a "survey" protocol or tissue segmentation algorithms. A survey protocol is required when searching for a lesion of unknown type or location. Segmentation requires unique signal signatures for tissues that may cover a broad range of tissue parameter values. Data acquisition is modeled as a mapping of a domain of tissue parameter values into a signal manifold in a signal strength space defined by the MRI protocol. The efficacy of the protocol is evaluated by investigating the characteristics of the signal manifold. A figure of merit which maximizes the probability of discriminating each point in the domain of tissue parameters from all others is developed.

Clinical Protocols↗
PubMed1990

Making magnetic resonance images and beyond.

Magnetic resonance (MR), a comparatively new imaging method in Canada, is based on physical principles that are different from all current imaging methods. An understanding of these principles is therefore essential to appreciate the clinical capabilities and limitations of MR. Because MR is a multiparameter imaging method, the challenge of choosing appropriate imaging sequences must be addressed. The technical development of anatomical image formation is now almost complete, so future research will focus on the use of MR to obtain more than just spatial information. The quantitative measurement of relaxation times, chemical composition, flow and spectra hold great promise in extending the capabilities of MR beyond those of other imaging methods.

Humans↗
PubMed1979

Comparison of the liver's respiratory motion in the supine and upright positions: concise communication.

The effect of the upright position, compared with the supine position, in reducing respiratory motion during liver scintigraphy has been measured in a group of 51 randomly selected patients. Little improvement in spatial resolution can be expected from simply standing the patient upright, and analog motion correction is recommended as much more effective in minimizing respiratory motion artifacts in liver scintigraphy.

Humans↗
PubMed1978

Optimization of analog-circuit motion correction for liver scintigraphy.

Respiratory motion customarily degrades the resolution of a routine hepatic scintigram. We have analyzed four analog motion-correction methods and have measured their abilities to maintain good spatial resolution over a broad range of liver scintigraphy parameters. The analog circuit described can maintain the spatial resolution of the scintillation camera within 2 mm of the full width at half maximum of the stationary point-sread function. Experiments show that clinicians require about 50% greater film-density contrast to detect a 2-cm-diam. lesion if motion correction is not used. In 14% of the cases studied, the addition of a motion-corrected anterior view to the usual four-view liver study (performed without motion correction) resulted in a changed clinical interpretation. We conclude that analog motion correction should be provided in all scintillation cameras used for liver scintigraphy.

Liver↗
PubMed1977

A quantitative measurement of peritoneal drainage in malignant ascites.

With a two-compartment model, a method is described for quantitative determination of peritoneal drainage rates in malignant ascites. Data on twenty-four patients are presented and comparison is made with the qualitative assessment of the integrity of diaphragmatic and mediastinal lymphatics on the basis of lymphoscintigrams. It is concluded that flow rates less than 50 ml/hour are usually associated with abnormalities of the diaphragmatic and mediastinal lymphatics, indicating that tumor permeation of these structures is a significant contributing factor to persistent, intractable ascites in patients with malignant diseases.

Ascites↗
PubMed1977

Compton scatter imaging of transverse sections: corrections for multiple scatter and attenuation.

The electron density (e cm-3) of a tissue sample can be determined by measuring the fluence of photons which it Compton scatters from a narrow incident beam of X- or gamma-radiation. This technique has been applied successfully to diagnostic denistometry (bone, lung), and less successfully to whole body tomography. In this work, the physics of Compton scatter tomography is examined with emphasis on transverse section scanning. The two major limitations of the scatter technique, attenuation of the single scatter photon fluence (of interest), and contamination of this fluence by multiply-scattered photons, are studied and corrective procedures are proposed. The methods described are applied to a simple test phantom; it is concluded that transverse images with an electron density precision of approximately 5% are possible.

Air↗
PubMed1977

Implications of computed tomography for inhomogeneity corrections in photon beam dose calculations.

Patient inhomogeneity information is investigated for use in radiotherapy planning. Absorbed doses measured in a phantom are compared to doses calculated for photon beams using various treatment planning inhomogeneity correction methods. Delineation of inhomogeneities with a spatial resolution of 5 mm and with an electron density accuracy of 2% in usually sufficient to allow doses to be calculated with a mean accuracy of better than 2% for 60Co and 3% for 25-MV x rays if the authors' Equivalent Tissue-Air Ratio Method is used.

Cobalt Radioisotopes↗
PubMed1975

The relationship between mouse arterial partial pressure of oxygen (PaO2) and the effectiveness of localized tumour irradiation.

The effectiveness of localized X-irradiation on the transplantable KHT sarcoma was investigated while the host mice breathed gas mixtures ranging from 5% O2 : 95% N2 to 100% O2. Subcutaneous tumours in the flank of C3H mice anaesthetized with Nembutal (sodium pentobarbitol), Valium (diazepam), or urethane, were irradiated with doses of 1,500 or 2,500 rads and the delay in days for the tumours to grow from 4 to 10 mm in diameter was determined. Measurements of the arterial partial pressure of oxygen (PaO2) were made under conditions identical to the irradiation experiments. For PaO2 values less than 100 mm Hg (animals breathing air), growth delay decreased linearly, while for PaO2 values greater than 100 mm Hg, growth delay increased and reached a plateau at a PaO2 between 200 and 300 mm Hg, (animals breathing congruent to 50% O2). This relationship holds for the two doses and the three anaesthetics studied, and indicates the importance of investigating the Pa02 levels of patients undergoing radiotherapy treatment.

Animals↗
PubMedDate not supplied

Use of magnetic particles for sensitizing MR images to blood flow.

Magnetic resonance (MR) images made with the IVIM (intravoxel incoherent motion) technique for demonstrating tissue microcirculation are limited in sensitivity because of the small volume of blood involved. This limitation may be overcome by incorporating magnetic particles into the flow. The magnetic perturbation caused by the particles extends beyond the walls of the capillary and affects a much larger volume than that of the flowing material. Imaging experiments conducted with an artificial capillary system for renal dialysis, containing large magnetic particles, showed that signal intensity decreased with increasing flow rate through the dialysis bundle and with increasing particle concentration. Predictions of the effect based on a theoretical model of spin dephasing in the field of a magnetic dipole agreed with the experimental data. The results hold promise for development of the technique in vivo.

Humans↗
PubMedDate not supplied

Identification of the periprostatic venous plexus by MR imaging.

T2-weighted images (spin echo 2,000/60) show a high signal intensity rim around the prostate. Our investigations show that this rim is not part of the pelvic fat; it has T1 and T2 relaxation times similar to heparinized blood; it demonstrates little inflow effect; and after an intravenous injection of Gd-diethylenetriamine pentaacetic acid, its signal intensity increases. We conclude that this rim is the periprostatic venous plexus.

Gadolinium↗