Functional imaging of the central auditory system using PET.

In the last few decades functional neuroimaging tools have emerged to study the function of the human brain in vivo. These techniques have increased the knowledge of how the brain processes stimuli of different sensory modalities, including auditory processing. Positron emission tomography (PET) has been used for nearly 20 years to study changes in cerebral blood flow associated with auditory stimulation in normal and hearing impaired subjects. PET studies gave insight into the neural base of processing basic sound features such as frequency and intensity, but complex stimuli such as speech and music have also been investigated extensively. Knowledge of the normal auditory function of the brain helps us to understand the neural base of hearing deficits and provides ideas for possible treatments. Although functional magnetic resonance imaging (fMRI) is replacing PET in many neuroimaging studies nowadays, PET still holds unique advantages and can give us valuable knowledge about the auditory cortex and auditory perception.

FDG-PET to evaluate response to hyperthermic isolated limb perfusion for locally advanced soft-tissue sarcoma.

UNLABELLED: We investigated FDG-PET in patients undergoing hyperthermic isolated limb perfusion (HILP) with rTNF-alpha, rIFN-gamma and melphalan for locally advanced soft-tissue sarcoma of the extremities. METHODS: Twenty patients (11 women, 9 men; aged 18-80 yr, mean age 49 yr) were studied. FDG-PET studies were performed before, 2 and 8 wk after HILP. After the final PET study, the tumor was resected and pathologically graded. Patients with pathologically complete response (pCR) showed no viable tumor after treatment. Those with pathologically partial response (pPR) showed various amounts of viable tumor in the resected specimens. RESULTS: Seven patients showed a pCR (35%) and 12 patients showed a pPR (60%). In one patient, pathological examination was not performed (5%). The pre-perfusion glucose consumption in the pCR group was significantly higher than in the pPR group (p<0.05). Visual analysis of the PET images after perfusion showed a rim of increased FDG uptake around the core of absent FDG uptake in 12 patients. The rim signal contained a fibrous pseudocapsule with inflammatory tissue in the pCR group, viable tumor was seen in the pPR group. The glucose consumption in the pCR group at 2 and 8 wk after perfusion had decreased significantly (p<0.05) in comparison to the glucose consumption in the pPR. CONCLUSION: Based on the pretreatment glucose consumption in soft-tissue sarcomas, one could predict the probability of a patient achieving complete pathological response after HILP. FDG-PET indicated the pathological tumor response to HILP, although the lack of specificity of FDG, in terms of differentiation between an inflammatory response and viable tumor tissue, hampered the discrimination between pCR and pPR.

Lower extremity angle measurement with accelerometers--error and sensitivity analysis.

Closed-loop control techniques for the restoration of locomotion of paraplegic subjects are expected to improve the quality of functional neuromuscular stimulation (FNS). We investigated the use of accelerometers for the assessment of feedback parameters. Previously, the possibility of angle assessment of the lower extremities using accelerometers, but without integration, was demonstrated. The current paper evaluates and assesses this method by an error and sensitivity analysis using healthy subject data. Of three potential error sources, the reference system, the accelerometers, and the model assumptions, the last was found to be the most important. Model calculations based on data obtained by the Elite video motion analysis system showed the rigid-body assumption error to be dominant for high frequencies (greater than 10 Hz), with vibrations in the order of 1 mm resulting in errors of one radial or more. For low frequencies (less than 5 Hz), the imperfect fixation of the accelerometers combined with a nonhinge type knee joint gave an error contribution of +/- 0.03 rad. The walking pattern was assumed to be two-dimensional which was shown to result in an error of +/- 0.04 rad. Accelerations due to rotations of the segments could be neglected. The total error computed for low frequencies (+/- 0.07 rad) was comparable to the experimental difference between the current and the reference system.

Automatic stance-swing phase detection from accelerometer data for peroneal nerve stimulation.

The development of implantable peroneal nerve stimulators has increased interest in sensors which can detect the different phases of walking (stance and swing). Accelerometers, having a potential for implantation, are studied as detectors for the swing phase of walking to replace footswitches. Theoretically, we could show that accelerometers can be used to distinguish between stance and swing phase. Attaching accelerometers between ankle and knee joint the equivalent acceleration of the ankle joint was calculated. This resulted in a typical and reproducible signal in which the different walking phases were identified. Automatic detection algorithms, based on cross correlation calculation were developed and tested. Measurements from four healthy and four hemiplegic subjects resulted in a total of 317 and 272 steps, respectively. One of the hemiplegic subjects was considered to be a failure due to large disturbances in the acceleration signal during the swing phase of walking, which may be related to the use of crutches. Taking part of the data as a learning set and the other part as an evaluation set we found two errors in the push-off detection for both the healthy subjects and the remaining three hemiplegic subjects, out of 152 and 106 steps, respectively. In addition, we showed that when using one accelerometer closely below the knee joint almost identical results can be achieved. This could lead to a combination of sensor and stimulator into one implantable device.

Real-time gait assessment utilizing a new way of accelerometry.

Real-time registration of body segment angles is essential in artificial body position control. A new method is presented for the real-time calculation of the lower extremity angles using data obtained from pairs of two one-dimensional accelerometers. It is shown that, assuming rigid-body dynamics and simple hinge joints, relative angles (i.e. angles between segments) can be calculated without integration, thereby solving the problem of integration drift normally associated with accelerometry. During the stance phase of walking, the relative angles can be transformed to absolute angles (i.e. relative to the gravitational field direction) for the different leg segments. The feasibility of relative angle calculation is demonstrated by calculation of the knee angle of a healthy subject. Stability and resolution were demonstrated with measurements during standing. Measurements during standing up, sitting down and walking showed that shock (heel-strike) and skin movements, due to movements of the underlying muscle tissue, are the main error sources. Additional signal processing, e.g. low-pass filtering, can be used to diminish this error. The accuracy of the knee angle found is shown to be high enough to be used in a feedback controller for functional electrostimulation of the lower extremities.