A cell pellet biophantom technique is introduced, and applied to the ultrasonic backscatter coefficient (BSC) estimate using Chinese hamster ovary (CHO) cells. Also introduced is a concentric sphere scattering model because of its geometrical similarities to cells with a nucleus. BSC comparisons were made between the concentric sphere model and other well-understood models for mathematical verification purposes. BSC estimates from CHO cell pellet biophantoms of known number density were performed with 40 and 80 MHz focused transducers (overall bandwidth: 26-105 MHz). These biophantoms were histologically processed and then evaluated for cell viability. Cell pellet BSC estimates were in agreement with the concentric sphere model. Fitting the model to the BSC data yielded quantitative values for the outer sphere and inner sphere. The radius of the cell model was 6.8 ± 0.7 μm; the impedance of the cytoplasm model was 1.63 ± 0.03 Mrayl and the impedance of the nuclear model was 1.55 ± 0.09 Mrayl. The concentric sphere model appears as a new tool for providing quantitative information on cell structures and will tend to have a fundamental role in the classification of biological tissues.

In patients with severe aortic stenosis (aortic valve area <1cm 2 or <0.6cm 2 /m 2 ) and high surgical risk (haemodynamic instability or significant co-morbidities), surgical aortic valve replacement is often rejected and, unfortunately, balloon valvuloplasty cannot provide a sustained improvement. Percutaneous heart valve (PHV) implantation is an excellent alternative treatment in such cases. The first successful human PHV implantation was performed in April 2002 by Cribier's group at Rouen University Hospital in France, via the antegrade (venous) transseptal approach. 1 Because of the complexity of the antegrade approach, several changes were introduced to implantation protocols. Subsequently, the arterial transfemoral and transapical delivery routes were developed. 2,3 The transapical approach is the most recently developed technique for transcatheter aortic valve replacement. This procedure involves a limited left lateral thoracotomy and requires a direct cardiac puncture and sheath Multidetector Computed Tomography Before Percutaneous Heart Valve Implantation CT works as a complement to echocardiography and conventional angiography. At our institution, the examination comprises two acquisitions: a cardiac assessment of the aortic valve immediately followed by abdominal and pelvic CT angiography, which is essential for assessing the retrograde route of the device. Other authors suggest performing only one acquisition. 5 AbstractPercutaneous implantation of an aortic valve has become a promising alternative treatment for patients with severe symptomatic aortic stenosis in whom conventional surgical treatment is contraindicated. A transfemoral or transapical delivery route can be chosen depending on the quality of vascular access and the type and size of prosthesis used. This article will mainly focus on the retrograde transfemoral approach, a technique with a high procedural success rate that is growing in popularity. Collaboration between radiologists and cardiologists is vital for a good outcome, and is mainly based on multidetector computed tomography (MDCT), which has quickly assumed a leading role in pre-implantation planning for inoperable severe aortic stenoses. The contribution of MDCT post-implantation is still under evaluation, but also seems promising. This article will discuss procedural techniques and clinical aspects of MDCT examination before and after percutaneous aortic valve implantation using the arterial transfemoral approach.

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