Classification of lower limb arterial stenoses from Doppler blood flow signal analysis with time-frequency representation and pattern recognition techniques

Totally Implantable Wireless Ultrasonic Doppler Blood Flowmeters: Toward Accurate Miniaturized Chronic Monitors

Totally implantable wireless ultrasonic blood flowmeters provide direct-access chronic vessel monitoring in hard-to-reach places without using wired bedside monitors or imaging equipment. Although wireless implantable Doppler devices are accurate for most applications, device size and implant lifetime remain vastly underdeveloped. We review past and current approaches to miniaturization and implant lifetime extension for wireless implantable Doppler devices and propose approaches to reduce device size and maximize implant lifetime for the next generation of devices. Additionally, we review current and past approaches to accurate blood flow measurements. This review points toward relying on increased levels of monolithic customization and integration to reduce size. Meanwhile, recommendations to maximize implant lifetime should include alternative sources of power, such as transcutaneous wireless power, that stand to extend lifetime indefinitely. Coupling together the results will pave the way for ultra-miniaturized totally implantable wireless blood flow monitors for truly chronic implantation.

Compensatory fuzzy neural networks-based intelligent detection of abnormal neonatal cerebral Doppler ultrasound waveforms

Compensatory fuzzy neural networks (CFNN) without normalization, which can be trained with a backpropagation learning algorithm, is proposed as a pattern recognition technique for intelligent detection of Doppler ultrasound waveforms of abnormal neonatal cerebral hemodynamics. Doppler ultrasound signals were recorded from the anterior cerebral arteries of 40 normal full-term babies and 14 mature babies with intracranial pathology. The features of normal and abnormal groups as inputs to pattern recognition algorithms were extracted from the maximum velocity waveforms by using principal component analysis. The proposed technique is compared with the CFNN with normalization and other pattern recognition techniques applied to Doppler ultrasound signals from various arteries. The results show that the proposed method is superior to the others, and can be a powerful technique to be used in analyzing Doppler ultrasound signals from various arteries.

Review of the assessment of single level and multilevel arterial occlusive disease in lower limbs by duplex ultrasound

The purpose of this article is to review the performance of duplex ultrasound scanning in assessing lower limb arterial disease with emphasis on patients with multisegmental occlusive lesions. Several studies have reported that duplex scanning can be as accurate as angiography to localize arterial stenoses. In spite of these promising results, there still remain some difficulties and controversies. Among them, it has been reported that multisegmental disease may affect the accuracy of duplex scanning. Indeed, some studies have indicated a lower sensitivity for detecting significant stenoses distal to severe or total occlusions. It also was demonstrated that second-order stenoses were detected with lower sensitivity compared to first-order stenoses. The main reason proposed to explain this lower sensitivity is that the highly reduced flow distal to occluded or highly stenotic segments increases the difficulty of detecting significant Doppler velocity changes in the distal or secondary stenoses. The intrinsic limitations of the peak systolic velocity ratio used as a classification criterion are presented. Finally, new and promising developments in power Doppler imaging and ultrasound contrast agents are discussed, because they may allow expansion of the capabilities of current ultrasound scanning systems and provide more accurate diagnosis of patients with multiple disease.

Lower extremity arterial evaluation: are segmental arterial blood pressures worthwhile?

PURPOSE

Physiologic observations with blood flow waveform analysis and pressure measurements can document the severity of lower extremity arterial disease. Segmental blood pressures (SEGPs) taken at the thigh, calf, and ankle are commonly used, but their utility has seldom been studied. We quantified improvements in accuracy compared with arteriography when ankle pressures alone (ABI) or SEGP data were added to velocity waveforms obtained by Doppler ultrasound.

METHODS

Continuous-wave Doppler velocity waveforms were recorded at common femoral (CFA), popliteal (POP), and dorsal pedal and posterior tibial (TIB) arterial levels. Systolic SEGP data were obtained with appropriately sized upper thigh, upper calf, and ankle cuffs. Waveforms, waveforms plus ABI, and waveforms plus SEGP data from 81 patients were randomly interpreted by 14 technologists or physicians from four institutions blinded to clinical and arteriographic data. Arteriograms were assigned negative or significant, severe (>75% diameter stenosis) values for four segments: iliofemoral (CFA), superficial femoral (SFA), popliteal (POP), and infrapopliteal (TIB) arteries. A total of 9072 segmental interpretations were analyzed.

RESULTS

Compared with arteriography, the accuracy of waveform analysis was 83% for severe disease at and proximal to the CFA, 79% for SFA disease, 64% for POP disease, and 73% for TIB disease. Adding ABI improved the accuracy significantly (p < 0.01) to 88% (CFA), 86% (SFA), 70% (POP), and 85% (TIB). Accuracy was inferior when SEGP data replaced ABI: 86% (CFA), 85% (SFA), 70% (POP), and 80% (TIB).

CONCLUSIONS

ABIs significantly improved Doppler waveform accuracy at all levels. Compared with ABI, the addition of segmental pressure to waveform data failed to improve accuracy. Pressure measurements above the ankle may lack cost effectiveness and clinical utility.

Quantitative assessment of abdominal aortic atherosclerosis observed in CT scans

Calcification of the aorta is characteristic of atherosclerotic disease. A novel numerical index for quantitating the extent of calcification observed in computed tomography (CT) scans has been developed. The index weights the fractional area of the aorta showing calcifications with the average calcium density in the plaques. It obviates the need for manual tracing of the calcifications, and avoids the arbitrary nature and lack of reproducibility of the "calcium score" system currently used in assessing CT scans. Continuously different levels of calcification were distinguished in the abdominal aortas of a group of Kuwaiti females (n = 20), with a linear correlation coefficient between index value and age of 0.914 (P < 0.0001) over three decades. The index is generally applicable to all arterial calcifications, and could be used to monitor the effect of therapeutic regimes. It could easily be modified for use with 3D reconstructions obtained from CT helical scanning or MRI.