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Biomedical subjects

M J Bronskill

Publications and source records attributed to M J Bronskill.

At least 55 records · Page 3Linked to original sources
PubMed1987

Application of an equivalent circuit to signal-to-noise calculations in MRI.

Transfer functions determined from the component values of an equivalent circuit are used to calculate the relative signal-to-noise ratio of rf coils for magnetic resonance imaging. Experimental verification of the method is obtained by directly measuring signals from three solenoidal coils and by measuring the signal-to-noise ratio of these solenoids. The transfer functions separate the total noise voltage into contributions from the coil resistance and contributions from magnetic and electric field interactions with the sample. The use of this technique in understanding and improving coil design is discussed.

Magnetic Resonance Spectroscopy↗
PubMed1987

Proton relaxation enhancement by manganese(III)TPPS4 in a model tumor system.

Managanese(III)tetraphenylporphine sulfonate [Mn(III)TPPS4] has been investigated as a tumor specific paramagnetic contrast agent for magnetic resonance imaging (MRI) of L1210 solid tumors in mice. Mn(III)TPPS4 was found to clear rapidly from the blood and concentrate in the kidneys, tumor and liver. Although relatively high ratios of tumor to normal tissues could be obtained (e.g., greater than 90 for tumor/muscle), the kidneys were found to have the highest concentration of the metalloporphyrin at all doses and time periods tested. A significant decrease in the longitudinal relaxation time was measured for excised tissues (kidney, tumor, liver, muscle) from mice that were treated with Mn(III)TPPS4. A linear correlation was observed between the longitudinal relaxation rate determined for L1210 tumor and the corresponding concentration of Mn(III)TPPS4 found at various injected doses and time intervals between the injection and analysis. A small animal radiofrequency receiver coil designed for use with a 0.15-T clinical imager was employed to evaluate the ability of Mn(III)TPPS4 to selectively increase the signal intensity of the implanted L1210 tumor. The images show a conspicuous enhancement in the contrast between the tumor and adjacent tissue upon treatment with this agent. The results indicate that Mn(III)TPPS4 is a useful prototype paramagnetic metalloporphyrin MRI contrast agent with a significant affinity for the L1210 tumor.

Animals↗
PubMed1987

Mediastinal lymph node metastases from bronchogenic carcinoma: detection with MR imaging and CT.

Magnetic resonance (MR) imaging and computed tomography (CT) were compared in a prospective study of 48 patients for the detection of metastatic mediastinal lymphadenopathy from bronchogenic carcinoma. The images were interpreted by three experienced radiologists using a five-point rating scale, enabling receiver operating characteristic (ROC) analysis. Imaging results were evaluated against "truth" data based on analysis of surgical specimens from mediastinoscopy and thoracotomy. All MR images were cardiac gated to reduce cardiac motion artifacts in the mediastinum. MR and CT both performed well, as indicated by similar areas under the ROC curves of 0.779 +/- 0.039 for MR imaging and 0.781 +/- 0.038 for CT scanning. No strong correlation between nodal size and metastatic involvement could be found for either MR or CT results. As long as nodal size remains the sole criterion in the detection of metastatic mediastinal lymphadenopathy, MR imaging is unlikely to enable better interpretations than CT scanning.

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

Optimal pulse sequence for imaging hepatic metastases.

For magnetic resonance (MR) imaging studies in which the diagnosis is dependent on image contrast, it is essential that an optimized imaging technique be used. Using detection of hepatic metastases as an example, the authors describe a rational strategy for optimizing MR imaging technique. First, for a single patient with proved hepatic metastases, a variety of imaging sequences is discussed and evaluated, leading to characterization of the patient's hepatic tissues. Then the characteristics of the tissues of a representative patient population are presented. These are used to determine two optimal pulse sequences that maximize the achievable signal difference-to-noise ratio achievable in a fixed imaging time. The recommended imaging sequence for detection of hepatic metastases at 0.15 T is either a three-dimensional volume spin-echo (SE) sequence with echo time (TE) = 12 msec and repetition time (TR) = 184 msec or a multisection inversion recovery sequence with TE = 22 msec, inversion time = 250 msec, and TR = 1,375 msec. The variation of this optimum pulse sequence with field strength is also presented.

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

In vivo measurements of NMR relaxation times.

A series of solenoidal NMR probes were built to measure T1 and T2 relaxation times in vivo in the mouse, over the frequency range of 5 to 60 MHz, using inversion-recovery and spin-echo pulse sequences. KHT tumors growing in the legs of C3H mice were studied and compared with normal mouse legs. The tumor relaxation times were studied at 10 MHz during the course of tumor growth and as a function of frequency when the tumor had a mass of approximately 0.9 g. Mouse legs with tumors have higher T1 and T2 values than those without tumors over the frequency range of 5 to 60 MHz. Significant changes in both relaxation times were detected before a palpable mass could be detected. T1 contrast between normal and tumor-bearing legs decreased with increasing frequency, while T2 contrast remained nearly constant. A comparison between in vivo and in vitro measurements was done using four different types of sample preparation: live mouse, dead mouse, excised whole mouse leg, and tissue sample. These studies showed small but significant differences between the relaxation times measured in vivo and those measured in vitro.

Animals↗
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↗
PubMed1983

Efficacy of computed tomography in the management of cancer patients.

An evaluation was made of 1030 computed tomography (CT) scans performed on cancer patients. Seventy percent of the scans taken were of the pelvis, abdomen, or thorax. Both referring clinicians and radiologists rated the diagnostic and management efficacy of each scan using a simple scale of values. Over 50% of the scans provided unique diagnostic information: 39% resulted in a change in diagnosis or in known extent of disease; and 14% led to a change in patient management. The fraction of abnormal results was not a reliable measure of efficacy. Specific groups of patients were identified, which demonstrated that both diagnostic and management efficacy should be measured in assessing the value of CT as a diagnostic modality.

Brain Neoplasms↗
PubMed1983

Radiation dose estimates for interstitial radiocolloid lymphoscintigraphy.

The spatial distribution of radioactivity in the injection site, and its rate of clearance, have been measured in patients undergoing various types of interstitial radiocolloid lymphoscintigraphy using 99mTc-antimony sulfide colloid. The clearance of radioactivity from the injection site, and the expansion with time of the localized radioactivity vary considerably for different sites of injection. Maximum absorbed dose estimates of 45.6 rads to the center of the injection site (rectus sheath) and 21 rads to individual lymph nodes have been calculated for patients undergoing internal mammary lymphoscintigraphy with 450 mu Ci injected radioactivity. Absorbed dose estimates for finger web, toe web, and perianal injection sites are also presented.

Antimony↗
PubMed1981

Discrepancies between radionuclide and computed tomographic scans in detecting secondary neoplastic involvement of the brain.

A radionuclide (RN) brain scan and a computed tomographic (CT) brain scan were performed on the same patient within one month on 207 occasions between February 1978 and October 1979 in order to investigate secondary neoplastic involvement of either metastatic or lymphomatous nature. The two scans were read independently of each other. There was a significant difference between the results of the two techniques in 26 of the 207 cases (13%). In 15 cases, the RN brain scan found clinically suspected secondary neoplastic involvement that was not detected by CT. In the other 11 cases, lesions detected by CT were not detected with the RN scan. Discrepancies were more frequent in patients with lymphoma than in patients with carcinoma.

Adult↗
PubMed1981

Compton scatter imaging of transverse sections: an overall appraisal and evaluation for radiotherapy planning.

A Compton scatter scanner has been developed to image electron density distributions of transverse body sections. The imaging performance of this device has been measured and compared with calculated limits and with the present capabilities of X-ray computed tomographic (CT) scanners. The use of Compton scatter images in radiotherapy dose calculations has been investigated and a calibration curve has also been measured from patient images to convert CT number data to electron densities for tissues in vivo. Images have been produced with a spatial resolution of 0.5 cm and an electron density accuracy of 4.3% for a radiation dose of 0.11 Gy (11 rad) to the patient. However, little potential remains for further development of the Compton scatter technique for whole-body imaging.

Decision Making↗
PubMed1980

Evaluation of computed tomography in oncology.

An evaluation was made of 1343 CT scans performed at The Princell Margaret Hospital using a 20-second body scanner. Six patient groups were defined according to the clinician's objective in ordering the scan, and to the relevance of symptoms to the region scanned. Computer-assisted analysis revealed that only by dividing patients into categories using three parameters (scan region, primary diagnosis and clinician's objective) did significant differences in the ratio of normal to abnormal CT scan results become apparent. Very specific groups of patients for whom CT is a low-yield procedure could be identified; nevertheless, further investigation showed that a normal CT result was of benefit in the management of these patients. The overall use of CT was efficacious and low diagnostic yield alone is not a sufficient measure of inappropriate use of CT.

Brain↗
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↗