Transcranial focused ultrasound (tFUS) is capable of providing subtherapeutic and therapeutic ablative treatments for a variety of brain disorders. A major challenge towards widespread use of tFUS-based therapies stems from the complexity of the skull that could result in severe loss of focusing gain. Using extensive hydrophone scan measurements in plain water as well as transskull, we have documented a range of tFUS beam distortions for a variety of target points and access angles. In this paper, we present quantitative measurements of tFUS distortions due to skull aberrations at different operating frequencies. In addition, refocusing results for a variety of target points at different frequencies within the transducer bandwidth are presented in terms of improvement in focusing gain. Dual-mode ultrasound array (DMUA) prototype (64 elements, concave with 40-mm radius of curvature) was used. Skull samples were extracted from animal subjects that have undergone tFUS treatments using the DMUA prototype were utilized. Experiments were performed at a set of 31 discrete frequencies in the range 2.0 MHz–5.0 MHz. A needle hydrophone was used to measure the pressure waveforms at the target locations. The element transmission efficiency varied as a function of frequency in a nonmonotonic manner with a range of 5–15 dB variation for the different target points. The array focusing gain also varied nonmonotonically suggesting the need for broadband refocusing.
carotid bodies (cBs) are chemoreceptors that monitor and register changes in the blood, including the levels of oxygen, carbon dioxide, and pH, and regulate breathing. enhanced activity of cBs was shown to correlate with a significant elevation in the blood pressure of patients with hypertension. CB removal or denervation were previously shown to reduce hypertension. Here we demonstrate the feasibility of a dual-mode ultrasound array (DMUA) system to safely ablate the cB in vivo in a spontaneously hypertensive rat (SHR) model of hypertension. DMUA imaging was used for guiding and monitoring focused ultrasound (FUS) energy delivered to the target region. In particular, 3D imaging was used to identify the carotid bifurcation for targeting the cBs. intermittent, high frame rate imaging during image-guided fUS (igfUS) delivery was used for monitoring the lesion formation. DMUA imaging provided feedback for closed-loop control (cLc) of the lesion formation process to avoid overexposure. The procedure was tolerated well in over 100 SHR and normotensive rats that received unilateral and bilateral treatments. the measured mean arterial pressure (MAp) exhibited measurable deviation from baseline 2-4 weeks post IgFUS treatment. The results suggest that the direct unilateral FUS treatment of the CB might be sufficient to reduce the blood pressure in hypertensive rats and justify further investigation in large animals and eventually in human patients.
Inspired by the low-difficulty of implementing a dual-branch selection combining (SC) technique, this research paper presents approximate closed form expressions for the bit error rate (BER) of M-ary phase shift keying (M-PSK) considering the SC technique. In particular, the BER expression is derived over independent and identically distributed (i.i.d) alpha - mu fading channels and is based on the use of Meijer’s G-function. The presented mathematical formulas can be modified to study the performance of different types of fading channels including Weibull, exponential, Nakagami-m, Gamma, and Rayleigh channels. This can be achieved by updating the parameters of the propagation medium nonlinearity (alpha) and the number of multipath clusters (mu). In addition, the paper provides numerical results that demonstrate a close match in the performance of the derived expressions and the simulation findings in terms of BER. Specifically, a very close to a total BER match is achieved using a range of signal to noise ratio (SNR) levels for various selections of the alpha and mu parameters. The obtained closed form BER expression of M-PSK considering the dual-branch SC technique is novel, new, and has never been published in the literature before.
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