Development and assessment of vascular phantoms for research and education

Abstract

Ultrasound practices encompass a wide variety of diagnostic and interventional procedures that increasingly fall under a wide variety of medical specialities. The major drawback of ultrasound use, is that considerable experience is required to gain the most from procedures. The skill of Ultrasound (U/S) operator is known to positively correlate with the number of scans performed. The practice of U/S is expanding in clinical medicine, and as a consequence, there is an increasing demand for education and training. Medical phantoms and simulators are rapidly expanding and are credited with improving safety and reducing medical errors. One of the most attractive areas where the medical phantoms and simulation systems could effectively help to achieve training goals and to improve practitioner skills in detection and diagnosis of variable disease is the vascular ultrasound applications. Duplex ultrasound is now recognised as a gold standard for many cardiovascular and peripheral vessel investigations. To establish our experience to deal with medical phantoms and build up knowledge to help us to use theoretical physics principles, an existing medical phantom was used. The Circle of Willis (CoW) replica was used to investigate the effects of occlusions on the cerebral blood flow in an anatomical replica of the circle of Willis. We succeeded to match the theoretical prediction of the peripheral resistance by adjusting the inlet pressure. The total cerebral flow was 444 mL/min in our model which is close to mathematical predicted value of 454 mL/min. The values and distribution of the anterior, middle, and posterior cerebral arteries were similar to mathematical measurements predicted by Alastruey. Our results suggest that the internal carotid artery (ICA) occlusion is more critical than the basilar artery occlusion and that the greatest reduction in the mean cerebral outflows occurred when the right ICA and contralateral anterior cerebral artery (A1) were occluded. As it has been known that ultrasound transducer of a single crystal with a frequency of around 2 MHz used for embolus detection in the Middle Cerebral Artery (MCA), but no specific transducer have been validated for embolus detection in Common Carotid Artery (CCA) yet. We used ultrasound as a diagnostic tool and carotid phantom in a novel study to investigate the sensitivity and specificity of embolus detection of Pulsed Waved probes in continuous monitoring of the common carotid artery. This was to establish validity and sensitivity of these Doppler transducers to detect solid embolic particles up to the size of 200 μm in a phantom of the common carotid artery. All the particles of 1000, 500, 200 μm diameter were detected and recorded by the fast speed camera. It was found that the particles of 1000μm and 500μm were detected with 100% sensitivity by 2MHz and 4MHz transducers. The 200 μm particles were detected with 94% sensitivity by 2MHz and 92% sensitivity and high specificity by 4 MHz transducers. The information from these studies could be used for the simultaneous monitoring of MCA and CCA with the use of 2 MHz probe to identify the active embolic signal source in patients with acute stroke. We successfully established the reliability of simultaneously monitoring of embolic signal from two sources. This monitoring technique could be used for monitoring patients with suspicion of Transient Ischemic Attack and all those who have had a stroke in acute stroke unit. The information and experience gained from the above investigations were used to develop a life size lower limb phantom. The phantom was subsequently used with a vascular simulator for the lower limb blood flow studies. Additionally, this setup was used to assess the scanning competency of novice vascular surgeon. Tissue mimicking materials were used to create life-size lower limb phantom that contains multilayers, skin-fat-muscle-bone and blood vessels. An extracorporeal circuit incorporating lower limb phantom and complex vascular simulator was set up to assess how effectively participants achieved training goals to improve their scanning skills in detection and diagnosis of peripheral vascular diseases in a life size leg phantom.