Intravascular Ultrasound Case Study

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2.5 Intravascular ultrasound:
Intravascular ultrasound (IVUS) is an imaging modality that uses ultrasound to generate realtime imaging of vascular structures. Images of the vascular lumen are obtained by placing a catheter with a miniature transducer on its distal end into a vessel. Vascular endothelium is assessed. IVUS makes use of capacitive micromachined ultrasound transducers (CMUT), which is based on energy transferal by a change in capacitance. Apte, Chang, Khuri-Yakub, Mioni, Nikoozadeh, Sarioglu & Zhuang (2014:107) states that CMUT are silicon micromachining processes with a ring shaped array utilized in intracardiac echocardiography (ICE) and IVUS. The ring shaped array provides the availability of a central endoscopic lumen through
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Fig. 1a. shows an IVUS probe with a single rotating transducer. Fig. 1.b shows a probe with a solid-state transducer array. Fig. 1c. shows an IVUS probe with a rotating annular transducer array.

Fig. 1: Schematic representations of existing and the proposed SL-IVUS probes. Courtesy of Degertekin, Hesler, & Karaman (2011:[n.p.]).

The mechanical type IVUS transducer is demonstrated in figure 2. This type of transducer makes use of rotating ultrasound sources. The ultrasound signal fills the entire vessel lumen while no signal interference presents.

Fig. 2: Mechanical Transducer Single transducer rotates on a drive shaft, 1900 rpm. Courtesy of Boston Scientific Corp ((n.d.):2).

Figure 3 below demonstrates a solid-state transducer, also known as a phased array, that makes use of flashing ultrasound sources. Interference of the ultrasound signal occurs, creating an area of no information called ringdown.

Fig. 3: Phased Array / Solid State Transducer Multiple (64) stationary transducers
Operating frequency and illustration and design. Courtesy of Boston Scientific Corp
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It takes a cross-sectional image of the vessel and allows the assessment of a percentage stenosis. The results of stenosis treatment can be evaluated by means of IVUS. It allows accurate assessment of re-stenosis following angioplasty and has resulted in the finding that a stent placement can prevent re-stenosis. Boston Scientific Corp ((n.d.):2) states that IVUS is applied in the investigation of lesion significance and lesions of which an angiographical determination could not be made. It serves as a guiding tool during stent placement and peripheral interventions. It allows the assessment of possible intra - or postoperative complications. With the aid of IVUS, disease progression and regression can be determined, cardiac transplant status can be evaluated and IVUS can be utelized in clinical research. The most common IVUS imaging is done on the coronary arteries. EUS-guided angiotherapy makes intravascular therapy possible and is done in conjunction with real time ultrasound investigation of thrombosis and hemostasis (Buthani,
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