Biomedical subjects

Kim Butts

Publications and source records attributed to Kim Butts.

7 recordsLinked to original sources

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↗

PubMed2003

Diffusion-weighted MRI after cryosurgery of the canine prostate. Magnetic resonance imaging.

PURPOSE: To evaluate the acute lesion created by cryosurgery with diffusion-weighted magnetic resonance imaging (DWI). MATERIALS AND METHODS: The appearance of the acute cryolesion was evaluated in four canine prostates DWI after they were warmed to original body temperature. The prostates were excised, stained with triphenyl tetrazolium chloride (TTC), photographed, prepared for hematoxylin and eosin (H&E) staining, and examined under a light microscope. RESULTS: A marked decrease in apparent diffusion coefficient of 38% was evident in the center of the previously frozen tissue, but not in all of the previously frozen tissue. Histologic results confirm differences between the iceball core and the periphery of the iceball, which have markedly different imaging characteristics on DWI. CONCLUSION: The core of the previously frozen tissue has a reduced apparent diffusion coefficient (ADC) compared to the periphery of the previously frozen tissue and previously unfrozen tissue.

Animals↗

PubMed2003

Pair of resonant fiducial markers for localization of endovascular catheters at all catheter orientations.

PURPOSE: To test wireless resonance circuits (RC) to be used as fiducial marker of endovascular catheters during MR-guided interventions. Current markers loose their signal enhancement for certain catheter orientations. The purpose of this study was to test a marker setup which overcomes this orientation problem. MATERIALS AND METHODS: The markers were constructed from a pair of two RCs. The RCs were individually tuned and the coil axes were oriented perpendicular to each other in order to decouple the two RCs. The markers were mounted on the tip of endovascular catheters and tested in vitro and in one porcine in vivo experiment. RESULTS: An intense MR signal at similar signal levels was noted at all catheter orientations. In the in vivo experiment the markers allowed for fast and reliable MR guidance of the catheters. CONCLUSION: A pair of two individually tuned and decoupled RCs is well suited for MR guidance of endovascular catheters.

Animals↗

PubMed2003

Triggered, navigated, multi-baseline method for proton resonance frequency temperature mapping with respiratory motion.

A technique is presented for the acquisition of temperature maps in the presence of variable respiratory motion using the proton resonance frequency (PRF) shift. The technique uses respiratory triggering, diaphragm position determination with a navigator echo, and the collection of multiple baseline images to generate temperature maps. Laser ablations were performed in an ex vivo liver phantom undergoing variable simulated respiratory motion and in vivo in four porcine livers, demonstrating a reduction of artifacts in the computed temperature maps compared with conventional single baseline techniques, both uncorrected and corrected for motion.

Animals↗

PubMed2003

Line scan diffusion imaging of the spine.

BACKGROUND AND PURPOSE: Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks. METHODS: Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay. RESULTS: All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi, (837 +/- 318) x 10(-6) mm(2)/s in the annuli fibrosi and ranged from 1019 x 10(-6) mm(2)/s to 1972 x 10(-6) mm(2)/s in benign compression fractures. The mean relative intra-participant variation of mean diffusivity among different vertebral segments (T10-L5) was 2.97%, whereas the relative difference in mean diffusivity among participants was 7.41% (P <.0001). The estimated measurement precision was <2%. A bi-exponential diffusion attenuation was found only in vertebral bodies. CONCLUSION: Line scan diffusion imaging is a robust and reliable method for imaging the spinal column. It does not suffer as strongly from susceptibility artifacts as does echo-planar imaging and is less susceptible to patient motion than are other multi-shot techniques. The different contributions from the water and fat fractions need to be considered in diffusion-weighted imaging of the vertebral bodies.

Adult↗

PubMed2002

Study of laser ablation in the in vivo rabbit brain with MR thermometry.

PURPOSE: To investigate the peak temperature and thermal dose (T(43)) as tissue damage indicators for thermal therapy. MATERIALS AND METHODS: The proton resonant frequency (PRF) shift thermal coefficient was calibrated on six in vivo rabbit brains during interstitial laser ablation. The peak temperature and T(43) were correlated with the lesion boundary observed on T2-weighted spin-echo (SE) MRI at 4 hours post-heating in seven thermal lesions using direct MR measurement and analysis based on a binary discriminate model. RESULTS: The peak temperature and T(43) were 48.3 +/- 1.7 degrees C and 191 +/- 219 minutes, respectively, from the direct MR measurement. The values derived by the binary discriminate analysis were 47.8 +/- 2.2 degrees C and 28 +/- 41 minutes, respectively. CONCLUSION: Our results suggest that tissue damage in rabbit brain 4 hours after thermal ablation can be predicted reliably from a threshold temperature of approximately 48 degrees C.

Animals↗

PubMed2002

Dynamic magnetic resonance guided treatment of developmental dysplasia of the hip.

This study demonstrates the feasibility and advantages of near real-time, multiplanar, dynamic magnetic resonance image-assisted treatment of patients with developmental dysplasia of the hip. Pathoanatomy and dynamic blocks to reduction are visualized with anatomic clarity not otherwise possible. Continuous imaging allows accurate assessment and maintenance of optimum positioning throughout the casting procedure. Patient charges for this new technique are less than standard methods of treatment, and the child receives no ionizing radiation.

Arthrography↗