Biomedical subjects
Publications and source records attributed to J R Fitzsimmons.
Coil development is fundamental to the optimization of imaging systems at any field; however, it is especially critical for low-field systems where signal strength is limited. Here we demonstrate a type of surface coil design which makes possible the acquisition of high-quality images of the neck and extremities.
Magnetic resonance imaging (MRI) demonstrated a fluid level within an aneurysmal bone cyst (ABC). Since the ABC contained gross blood at operation, an anticoagulated human blood sample was studied by MRI also, and a fluid level was again clearly visible. MRI pulse sequences emphasizing T1 contrast showed the fluid levels most clearly in both the ABC and the blood. Sequences emphasizing T2 contrast showed homogeneous, bright signals in the ABC and in the blood, with no visible fluid level in the ABC and a nearly invisible one in the blood. In the blood sample, the calculated plasma T1 value was 1585 ms, and that of the red cells was 794 ms.
An analysis of the effects of multisection-multiecho imaging on signal intensity is presented using a gaussian excitation pulse. The number of sections acquired, size of the intersection gap, and the number of echoes were all varied independently to evaluate their effect on image intensity. The results indicate that one should take a conservative approach in multisection-multiecho imaging, leaving at least a 2-mm-intersection gap and approximately a 20-msec delay between section excitations to avoid image signal loss owing to partial saturation effects.
Seventeen patients with suspected ovarian masses were evaluated by magnetic resonance imaging (MRI). MRI findings were confirmed by surgery (13 patients) or sonography and clinical follow-up (four). The study evaluated MRI characteristics of ovarian lesions using recently developed multislice and multiecho pulse techniques for a 0.15-T system. T1 and T2 relaxation times were calculated in 12 patients and although a range of values was obtained in several disease categories, diagnostic accuracy was frequently improved. MRI appearances tended to vary considerably with different pulse sequences and were particularly complex in patients with endometriosis and cystic ovarian tumors. Shortest calculated T1 and T2 values were found in hemorrhagic cysts in patients with endometriosis. Benign tumors with thick fibrous pseudocapsules had longer T1 values. Inflammatory masses and malignant ovarian tumors had significantly longer T1 and T2 values and relaxation times in a patient with mucinous cystadenoma varied within the complex mass.
In an experimental animal model of partial ureteral obstruction, three different modalities--excretory urography, real-time ultrasound and magnetic resonance--were used for imaging of the unilateral hydronephrotic rabbit kidney. Urography demonstrated well the anatomy of the renal pelvis, the site and the degree of obstruction. Real-time ultrasound and magnetic resonance imaging were both capable of demonstrating compartments of renal parenchyma in addition to the pelveocaliceal dilatation. With magnetic resonance, the renal vessels could be demonstrated. Blood flow velocity in renal arteries and veins was determined with the Doppler technique.
A receiver coil of a cross-coupled, double loop geometry has been developed. This coil has a higher signal-to-noise (S/N) ratio and more homogeneous signal intensity at increasing depth than a conventional surface coil. Improvements in S/N of 51-256% compared with the commercial half-saddle body coil have been demonstrated in a 0.15 T resistive instrument. The new coil permits reduction in pixel volume using higher field gradients and thinner slices or time savings using fewer signal averages. The double loop coil provided higher S/N for lumbar spine imaging than an oval surface coil. Limitations of this type of coil design are increased sensitivity to respiratory motion artifacts and limitation of the size of the subject that may be imaged. Using the double loop coil, the capability of our instrument to image the heart, pelvis, hip, and shoulder has been substantially improved.
Signal intensity (SI) variability was evaluated on a 0.15-T resistive instrument using a phantom and was found to increase with time, repetition time (TR), and echo time (TE), ranging from 0.24% standard deviation (SD) over 34 min for 500/30 (TR/TE) images, to 2.1% SD over 5 days for 2000/30 images. Signal-to-noise (S/N) variability increased with time and TE but not TR and ranged from 4.2% SD over 34 min to 7.1% SD over 5 days in 500/30 images. Variability in T1 and T2 measurements on phantoms ranged from 1.8% to 4.8% SD for T1 and 3.6% to 6.5% SD for T2 in the biological range over 5 h. High reproducibility of SI, T1, and T2 measurements was demonstrated over a 6-week period in normal muscle measurements.
The value of magnetic resonance imaging (MRI) in the diagnosis of renal abscess was investigated in an experimental animal model. MRI is capable of depicting the location and extent of the inflammatory process using T1 weighted scans because of relatively long T1 relaxation values which were significantly longer than T1 relaxation times of adjacent normal renal parenchyma.
The recent development of improved commercial radiofrequency coils and multiecho, multislice software for low field strength magnetic resonance systems has markedly increased the clinical utility of magnetic resonance imaging (MRI) of the pelvis at low field strengths. An evaluation of 70 patients with a variety of pelvic lesions and 14 normal volunteers who were studied using 0.15 T resistive magnet scanner revealed that anatomic structures and a variety of mass lesions could be clearly depicted in transaxial, sagittal and coronal planes using this updated system. Accurate characterization of lesions was possible in many instances using T2 weighted multiecho scans with echo time (TE) ranging from 30 ms to 120 ms (45 ms-180 ms using a reduced bandwidth technique). T1 weighted multislice scans demonstrated anatomic structures to best advantage and calculation of T1 and T2 relaxation times frequently facilitated more accurate differential diagnosis, particularly in the case of ovarian lesions.
The rapid proliferation of nuclear magnetic resonance imagers necessitates an increasingly critical look at system requirements. Image quality in its broadest sense must be determined for various types of imaging systems. We review here the physical determinants of image quality and present examples of images acquired at several different field strengths.
Experimental renal carcinoma was induced by percutaneous injection of VX-2 carcinoma cells into the left kidney in New Zealand white rabbits. Magnetic resonance imaging (MRI) was performed at 0.15 T before and after intravenous injection of 0.3 mmol gadolinium-DTPA (Gd-DTPA) per kg body weight. Gd-DTPA enhanced the tumors by increasing the signal intensity on T1 weighted images. The enhancement was evident immediately after Gd-DTPA injection, increasing during the observation time of 30 minutes. Histologically the areas of enhancement corresponded well to the viable tumor tissue.
Serial hippuran renograms were performed in pediatric allograft recipients in an effort to detect the onset of rejection following the initial 3 month post transplant period. The plots of the normalized effective renal plasma flows (NERPF) were compared with reciprocal of the serum creatinines. A strong correlation was noted between both values. NERPF could be predicted from the serum creatinine utilizing a logarithmic equation. However, there was no detectable difference between the onset of changes in the slopes of either variable. Therefore, serial hippuran renograms were no better than monitoring serum creatinine in detecting allograft dysfunction when performed at the frequency of the study.