| This research exploits the area of indicator dilution and blood flow modeling using positron emission tomography to quantitatively assess the dynamics of arterial and regional muscle blood flow in the dysvascular amputee. This proof-of-concept methodology study demonstrates the applicability of using the gamma-variate and Kety-Schmidt modeling techniques to understand the physiological implication of using an advanced prosthetic system, a vacuum-assisted suspension system (VASS). For this study, three amputee subjects were randomly assigned to a control group and three to an experimental group. The control subjects were imaged upon admission into the study, thirty days later (prior to wearing a VASS system), and thirty days after wearing the VASS system. The experimental subjects were imaged upon admission to the study (prior to wearing the VASS system), fitted with the VASS, and re-imaged thirty days after wearing the VASS system. Each imaging session consisted of four bolus H2 15O injections, two at rest and two after isometric exercise. The indicator dilution dynamics were modeled using the gamma variate function to assess the dynamics of the injected tracer in both the sound and residual limbs. After removing the recirculation portion of the indicator dilution curve, each curve was successfully fitted with the gamma variate function. From the fitted models, the peak, arrival, departure, and mean transit times were calculated. All of the calculated dispersion information was assessed for significance between sessions, with emphasis on the difference in arrival time of the tracer. The Kety-Schmidt model was utilized to determine the regional muscle blood flow. An accurate arterial input function is critical in the models ability to quantify blood flow. This study demonstrated the use of an image derived input function in the lower extremity. Because of the limited spatial resolution of positron emission tomography, it is essential to account for the partial volume effect when using an image derived input function. A novel method to assess a subject specific recovery coefficient based on equilibrium of the tracer was utilized. Subsequently the arterial input function was corrected and the regional muscle blood flow was determined for each session at rest and after exercise. A limited comparison (due to the sample size) on the hemodynamic effects of using a VASS after thirty days is described. Significance in the regional muscle blood flow after use of the VASS was demonstrated in the residual limb. This suggests that use of an advanced prosthetic system may influence the health outcome of an amputated limb. |
