In open surgical procedures, image-ablate ultrasound arrays performed thermal ablation and imaging on rabbit liver lobes with implanted VX2 tumor. Treatments included unfocused (bulk ultrasound ablation, N = 10) and focused (high-intensity focused ultrasound ablation, N = 13) exposure conditions. Echo decorrelation and integrated backscatter images were formed from pulse-echo data recorded during rest periods after each therapy pulse. Echo decorrelation images were corrected for artifacts using decorrelation measured prior to ablation. Ablation prediction performance was assessed using receiver operating characteristic curves. Results revealed significantly increased echo decorrelation and integrated backscatter in both ablated liver and ablated tumor relative to unablated tissue, with larger differences observed in liver than in tumor. For receiver operating characteristic curves computed from all ablation exposures, both echo decorrelation and integrated backscatter predicted liver and tumor ablation with statistically significant success, and echo decorrelation was significantly better as a predictor of liver ablation. These results indicate echo decorrelation imaging is a successful predictor of local thermal ablation in both normal liver and tumor tissue, with potential for real-time therapy monitoring.
Elevated vacuum (EV) is a promising technology in the field of prosthetics. It has been shown to improve the fit of the limb in the socket, resulting in many possible benefits to the function of a prosthesis. However, very little research has been done on its effect on patient function. This unique case report documents the effect on one patient's function of transitioning from a patella-tendon-bearing (PTB) socket with ischial weightbearing thigh cuff (IWBTC) to a prosthesis with an EV socket system. The patient underwent a transtibial amputation as a result of an avulsive trauma and used the PTB socket and thigh cuff for 16 years. In an effort to correct the patient's gait and improve his ability to perform the necessary tasks of his occupation, farming, the patient began using an EV prosthesis. He was interviewed and his functional status was evaluated 1 week, 1 month, and 1 year after receiving the prosthesis. After 1 week, the patient showed improvement in skin condition and expressed increased confidence in difficult locomotor tasks. At 1 month, he was no longer experiencing pain in his sound side knee and his gait symmetry had improved dramatically. After 1 year, the patient showed further improvement in gait and balance as well as the ability to wear the prosthesis comfortably for 24 hours at a time when necessary for his occupation. The transition from a PTB with IWBTC prosthesis to an EV system dramatically improved this patient's functional outcome and lessened the negative effects associated with wearing a prosthesis. (J Prosthet Orthot. 2011;23:184 -189.) KEY INDEXING TERMS: lower limb, prosthetics, function, outcomes, vacuum, subatmospheric I t is the goal of all prosthetic interventions to maximize patient function. Research has shown that physical mobility is the only independent factor that significantly affects quality of life in amputees when compared with nondisabled persons. 1 Although they theoretically have the highest probability of achieving normal functioning, 2 patients who have undergone amputation due to an avulsive trauma generally have secondary injuries that complicate their recoveries. For transtibial amputees, injuries typically include extensive damage to the patellar tendons and hamstring group. It is possible to accommodate for the resulting gait deficiencies with a patellatendon-bearing (PTB) socket connected to an ischial weightbearing thigh cuff (IWBTC) with external knee joints and check strap (Figure 1). In this type of prosthesis, the external knee joints and check strap combine to prevent knee hyperextension in the PTB socket, accommodating the hamstring group weakness. The forces responsible for hyperextension on the residuum are countered by the check strap. 3Alternatively, there is an emerging technology that shows promise as a replacement for traditional prosthesis designs: elevated vacuum (EV). Also known as subatmospheric, EV prostheses consist of an elastomeric liner, total surface bearing socket, mechanical or electronic vacuum pump, and a sealing sleeve. Des...
Measurement of in situ spatiotemporal temperature profiles would be useful for developing and validating thermal ablation methods and therapy monitoring approaches. Here, finite difference and analytic solutions to Pennes’ bio-heat transfer equation were used to determine spatial correlations between temperature profiles on parallel planes. Time delays and scale factors for correlated profiles were applied to infrared surface-temperature measurements to estimate subsurface temperatures. To test this method, exvivo bovine liver tissue was sonicated by linear image-ablate arrays with 1–6 pulses of 5.0 MHz unfocused (7.5 s, 64.4–92.0 W/cm2 in situ ISPTP) or focused (1 s, 562.7–799.6 W/cm2 in situ ISPTP, focus depth 10 mm) ultrasound. Temperature was measured on the liver surface by an infrared camera at 1 fps and extrapolated to the imaging/ablation plane, 3 mm below the surface. Echo decorrelation maps were computed from pulse-echo signals captured at 118 fps during 5.0 s rest periods beginning 1.1 s after each sonication pulse. Tissue samples were frozen at −80 °C, sectioned, vitally stained, imaged, and segmented for analysis. Estimated thermal dose profiles showed correspondence with segmented tissue histology, while thresholded temperature profiles corresponded with measured echo decorrelation. These results suggest utility of this method for thermal ablation research.
Echo decorrelation imaging is a pulse-echo method that maps millisecond-scale changes in backscattered ultrasound signals, potentially providing real-time feedback during thermal ablation treatments. Decorrelation between echo signals from sequential image frames is spatially mapped and temporally averaged, resulting in images of cumulative, heat-induced tissue changes. Theoretical analysis indicates that the mapped echo decorrelation parameter is equivalent to a spatial decoherence spectrum of the tissue reflectivity, and also provides a method to compensate decorrelation artifacts caused by tissue motion and electronic noise. Results are presented from experiments employing 64-element linear arrays that perform bulk thermal ablation, focal ablation, and pulse-echo imaging using the same piezoelectric elements, ensuring co-registration of ablation and image planes. Decorrelation maps are shown to correlate with ablated tissue histology, including vital staining to map heat-induced cell death, for both ex vivo ablation of bovine liver tissue and in vivo ablation of rabbit liver with VX2 carcinoma. Receiver operating characteristic curve analysis shows that echo decorrelation predicts local ablation with greater success than integrated backscatter imaging. Using artifact-compensated echo decorrelation maps, heating-induced decoherence of tissue scattering media is assessed for ex vivo and in vivo ultrasound ablation by unfocused and focused beams.
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