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Biomedical subjects

M J Bronskill

Publications and source records attributed to M J Bronskill.

At least 19 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↗
PubMed1989

Spin locking for magnetic resonance imaging with application to human breast.

The dependence of rotating frame spin-lattice relaxation, T1 rho on locking field frequency, f1, was measured for phantom materials and human breast tissues. These data were used to predict the relative signal strengths obtainable in a spin-locking imaging sequence. This imaging sequence was implemented on a 0.15-T imaging system and measurements of phantom and tissue signal strength for various imaging parameters agreed with predicted signal strengths. Compared to T1 and T2, T1 rho appears to have unique capability to distinguish tumor from normal fat and fibrous breast tissues. The applications of T1 rho to tissue characterization and imaging at high static field strengths are discussed.

Adipose Tissue↗
PubMed1988

Magnetic resonance imaging, computed tomography, and radionuclide scintigraphy in detection of liver metastases.

A series of 100 patients with suspected hepatic metastases was studied with magnetic resonance (MR), unenhanced computed tomography (CT), and radionuclide (RN) scintigraphy. Each set of images was read by three clinicians using a five-point scale to allow receiver operating characteristic (ROC) analysis using truth data derived from clinical review. Performance was measured by the areas under the ROC curves (0.940 +/- .018 for MR, 0.951 O +/- .013 for CT and 0.943 +/- .013 for RN) which were statistically not significantly different. We conclude that at their present level of development these three diagnostic examinations have equivalent performance and that MR is not superior in the detection of hepatic metastases.

Evaluation Studies as Topic↗
PubMed1988

MRI of periprostatic venous plexus in staging of early prostatic carcinoma.

The periprostatic venous plexus can be observed as a bright rim in coronal magnetic resonance (MR) images obtained by spin-echo (SE) 2060/60 technique. A carcinoma of the prostate which penetrates through the capsule into the periprostatic tissues interrupts or obliterates this rim, whereas an intact rim indicates that the tumor is confined within the prostatic capsule. One hundred patients with proven prostatic carcinoma were prospectively imaged by MR to detect periprostatic involvement. The results were compared with those obtained by cystoscopy and digital rectal examination under general anesthesia. The imaging and clinical methods agreed with each other in 76% of the patients.

Adult↗
PubMed1987

Magnetic resonance imaging of retroperitoneal lymphadenopathy.

A prospective study was performed to determine the value of magnetic resonance imaging (MRI) in the detection of retroperitoneal lymphadenopathy. Fifty patients with known malignancy, who demonstrated enlarged lymph nodes on computed tomography (CT), were entered into the study. The best visualization of retroperitoneal lymphadenopathy was found with a multislice spin-echo pulse sequence having a repetition time of 2000 msec, and echo delay of 30 msec. Nodes had a signal intensity lower than fat and greater than muscle with this pulse sequence. More than 90% of the lymphadenopathies as shown by CT could be demonstrated by MRI. Due to the flow-void phenomenon, blood vessels did not have any signal and were easily visualized without the use of intravenous contrast medium. Sagittal and coronal images added to an appreciation of the size of nodes and the extent of retroperitoneal lymphadenopathy. Ten normal volunteers were also imaged by MRI and their retroperitoneal nodes were well demonstrated.

Humans↗
PubMed1986

Magnetic resonance imaging of the mediastinum.

Seven normal volunteers and 69 patients with known disease in either the mediastinum or hila or both were imaged using a prototype magnetic resonance imager operating at 0.15T. Normal mediastinal and hilar structures were readily identified and mediastinal diseases were well demonstrated by magnetic resonance imaging (MRI). The value of MRI lies in the morphological demonstration of the presence and extent of disease.

Adult↗
PubMed1985

Magnetic resonance imaging of the prostate.

Twenty-two normal volunteers and 32 patients with either benign prostatic hypertrophy or prostatic carcinoma were examined by magnetic resonance imaging (MRI). The images were of high quality and clearly demonstrated the prostate gland and the surrounding anatomy but were of limited value in differentiating between benign and malignant prostatic disease. Using a specific pulse sequence, the authors were able to visualize what they believed to be the periprostatic venous plexus and suggest that the demonstration of this venous plexus may be of value in showing extraglandular spread of carcinoma of the prostate.

Aged↗
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↗