Biomedical subjects

Graham Sommer

Publications and source records attributed to Graham Sommer.

4 recordsLinked to original sources

PubMed2004

Highly directional transurethral ultrasound applicators with rotational control for MRI-guided prostatic thermal therapy.

Transurethral ultrasound applicators with highly directional energy deposition and rotational control were investigated for precise treatment of benign prostatic hyperplasia (BPH) and adenocarcinoma of the prostate (CaP). Two types of catheter-based applicators were fabricated, using either 90 degrees sectored tubular (3.5 mm OD x 10 mm) or planar transducers (3.5 mm x 10 mm). They were constructed to be MRI compatible, minimally invasive and allow for manual rotation of the transducer array within a 10 mm cooling balloon. In vivo evaluations of the applicators were performed in canine prostates (n = 3) using MRI guidance (0.5 T interventional magnet). MR temperature imaging (MRTI) utilizing the proton resonance frequency shift method was used to acquire multiple-slice temperature overlays in real time for monitoring and guiding the thermal treatments. Post-treatment T1-weighted contrast-enhanced imaging and triphenyl tetrazolium chloride stained tissue sections were used to define regions of tissue coagulation. Single sonications with the 90 degrees tubular applicator (9-15 W, 12 min, 8 MHz) produced coagulated zones covering an 80 degrees wedge of the prostate extending from 1-2 mm outside the urethra to the outer boundary of the gland (16 mm radial coagulation). Single sonications with the planar applicator (15-20 W, 10 min, approximately 8 MHz) generated thermal lesions of approximately 30 degrees extending to the prostate boundary. Multiple sequential sonications (sweeping) of a planar applicator (12 W with eight rotations of 30 degrees each) demonstrated controllable coagulation of a 270 degrees contiguous section of the prostate extending to the capsule boundary. The feasibility of using highly directional transurethral ultrasound applicators with rotational capabilities to selectively coagulate regions of the prostate while monitoring and controlling the treatments with MRTI was demonstrated in this study.

Acoustics↗

PubMed2004

Referenceless PRF shift thermometry.

The proton resonance frequency (PRF) shift provides a means of measuring temperature changes during minimally invasive thermotherapy. However, conventional PRF thermometry relies on the subtraction of baseline images, which makes it sensitive to tissue motion and frequency drift during the course of treatment. In this study, a new method is presented that eliminates these problems by estimating the background phase from each acquired image phase. In this referenceless method, a polynomial is fit to the background phase outside the heated region in a weighted least-squares fit. Extrapolation of the polynomial to the heated region serves as the background phase estimate, which is then subtracted from the actual phase. The referenceless method is demonstrated on a phantom during laser heating, 0 degrees temperature rise images of in vivo human liver, interstitial laser ablation of porcine liver, and transurethral ultrasound ablation of canine prostate. A good correlation between temperature maps reconstructed with the referenceless and subtraction methods was found.

Animals↗

PubMed2004

Measurement of renal extraction fraction using contrast-enhanced computed tomography.

Renal extraction fraction (EF) is the percentage of plasma entering the glomerulus which is filtered. Contrast agents which are freely filtered and neither secreted nor reabsorbed, may be used as markers for renal filtration, allowing EF to be calculated from computed tomography (CT) measurements of systemic vessels and renal veins. CT scans of 10 adult patients having no known renal disease were studied in this manner, giving EF values averaging 12.6% and 12.3% for the right and left kidneys, respectively, compared to the accepted value of 15%-20%. EF measurement using CT may provide noninvasive evaluation of renal function, complementing CT-derived morphologic information.

Adult↗

PubMed2003

Evaluation of renal growth by magnetic resonance imaging and computerized tomography volumes.

PURPOSE: Magnetic resonance imaging (MRI) and computerized tomography (CT) are commonly used to image complex medical conditions but limited data have been reported concerning normal renal volumetric measurement with these imaging techniques. We examined whether normative renal growth curves could be constructed from data derived from these imaging modalities, and from these curves assessed normal and abnormal renal development. MATERIALS AND METHODS: Patients who had undergone prior renal MRI or CT were identified. Total renal volume and renal cortical fraction (CF, cortical/total volume) were calculated, and growth curves were derived. To examine the curve utility for abnormal growth assessment, renal ultrasonography of children with reflux nephropathy was examined, and MRI and radionuclide scans were compared. RESULTS: A total of 60 patients 2 months to 39 years old who underwent MRI were included in the growth curve. The CF of the 120 kidneys was 75.8 +/- 4.3% and independent of sex and age. In 19 patients with vesicoureteral reflux 13 kidneys had cortical scarring, and the CF was decreased (p <0.001, 63.65 +/- 5.72%), indicating disproportionate cortical loss. No difference between CF for normal and vesicoureteral reflux unscarred kidneys was found. Differential renal function on radionuclide study correlated highly with MRI renal volume (r = 0.91). CT was performed in 70 children 1 to 15 years old (mean age 7.9) volume correlated with age and renal length, and the left kidney was larger than right kidney on MRI and CT. CONCLUSIONS: Normative renal growth curves can be constructed from CT and MRI derived renal volumes. Cortical fraction is consistent, and sex and age independent. In reflux nephropathy the CF is reduced and renal differential function on nuclear scan correlates with MRI derived differential volume. This concept may be useful for predicting abnormal renal growth and differential function.

Adolescent↗