Polyethylene-based Water- and Bone-equivalent Materials for Calibration Phantoms in Quantitative Computed Tomography - Ein Kalibrierphantom für die quantitative Computertomographie aus wasser- und knochenäquivalentem Material

Abstract

Polyethylene-based water-and bone-equivalent plastics for Calibration phantoms in quantitative computed tomography (QCT) were optimized by calculation and experimental verification A composition of 91.3 % polyethylene, 5.5 % CaCO 3 , and 3.2 % MgO (by weight) was accepted äs being water-equivalent with respect to absolute value and energy dependence of the X-ray attenuation coeff icient; the material was compared to other commercially available solids. Boneequivalent samples containing 200 mg of hydroxyapatite per ml were obtained by adding the mineral powder to the water-equivalent material. A procedure for industrial mass production of both materials was developed. A first application of these materials is given by a new QCT Calibration phantom. Schlüsselwörter: Hydroxylapatit, Kalibrierung, Knochen, Mineralsalzbestimmung, Polyäthylen, Phantom, quantitative Computertomographie Durch Berechnung und experimentelle Untersuchungen wurde ein Eichphantom für die quantitative Computertomographie optimiert. Es handelt sich um einen festen Körper, dessen Grundmaterial Polyäthylen ist, aus welchem ein wasser-und knochenäquivalentes Material hergestellt wurde. Eine Mischung aus 91,3% (Gewichtsprozent) Polyäthylen, 5,5% CaCO 3 und 3,2 % MgO wurde für das wasseräquivalente Material verwendet. Die Übereinstimmung mit Wasser bezieht sich sowohl auf den absoluten Schwächungswert als auch auf dessen Abhängigkeit von der Energie der Röntgenstrahlen. Das Material wurde mit anderen kommerziell erhältlichen verglichen. Für die Knochenäquivalenz wurde dem Grundmaterial 200 mg Hydroxylapatit pro ml beigemischt. Zur industriellen Herstellung wurde ein Produktionsprozeß entwickelt, der hohe Homogenität garantiert. Das Material findet Verwendung in einem neuen QCT-Kalibrierphantom. IndroductionWater-and tissue-equivalent materials were first proposed and developed for radiation dosimetry purposes [11]. Equivalence of a synthetic material to a tissue or material of interest is assumed if the attenuation or energy absorption characteristics of the two respective materials are the same for a defined type of radiation. In the context of this paper, we will consider the equivalence of materials with respect to the linear X-ray attenuation coeff icient// over the energy ränge of 30 to 150 keV which is relevant to diagnostic X-ray procedures. The aim was to obtain calibration materials for QCT. Calibration phantom techniques for QCT, äs introduced by Genant and Cann, serve to control apparatus stability and to provide a calibration surve for conversion of CT numbers, measured in Hounsfield units (HU) f into bone mineral density (BMD) values, specified in mg/cm 3 [1]. The Cann/Gcnant phantom, developed for verlebral bone mineral measurement, consists of a perspex body containing bore holes filled with aqueous Solutions of ^HPO-t. Concern about the long-term stability of these Solutions gave rise to other groups' investigations [7,8,9] and to our efforts regarding the development of solid materials.The particular requirements for our work were t...

Classification of X-Ray Attenuation Properties of Additive Manufacturing and 3D Printing Materials Using Computed Tomography From 70 to 140 kVp

“…However, this is more easily achieved for projective imaging, where in most cases it is sufficient to imitate the mass attenuation coefficient and possibly add air gaps as was done in the simple slab phantoms used for dosimetry and dose audits, like the NEXT and CDRH phantoms ( Suleiman et al, 1999 ; Spelic et al, 2004 ; IAEA, 2007 ), than for computed tomography where the linear attenuation coefficient needs to imitated ( Homolka and Nowotny, 2002 ). The latter usually results in the necessity of lowering the mass density if soft tissues or water are imitated by adding filling materials with very low density if curable liquid resins were used ( White et al, 1977 ), or using low density thermoplastic polymers or a mixture of these ( Kalender et al, 1988 ; Homolka and Nowotny, 2002 ). In castable resin based materials mimicking soft tissue or water, typically hollow air filled phenolic microspheres were used ( White et al, 1977 ).…”

A formulation of tissue- and water-equivalent materials using the stoichiometric analysis method for CT-number calibration in radiotherapy treatment planning

“…A material is considered equivalent to a real tissue if it has the same radiation characteristics within the relevant energy range in addition to similar physical properties such as mass density and electron density. Many phantom materials have been developed for this purpose; their base materials are often polymers, specifically epoxy resin (White et al 1977, Constantinou et al 1982, Goodsitt et al 1991, Süß and Kalender 1996, Jones et al 2003, polyethylene (Hermann et al 1983, 1985, 1986, Kalender and Suess 1987, Kalender et al 1988, Burmeister et al 2000 and other compounds include paraffin wax, polystyrene, polypropylene and polyurethane (White 1977, Iwashita 2000, Homolka and Nowotny 2002, Homolka et al 2002a, 2002b, Wucherer et al 2010. In addition to that, ICRU Report 44 (ICRU 1989) has compiled several other materials that can be used as tissue substitutes.…”

Optimization of the composition of phantom materials for computed tomography

“…Processing conditions (temperature, pressure) also show some influence on the density of polymers (e.g. 0.5% for polyethylene-based phantom materials, Kalender et al (1988)).…”

“…Most phantom materials developed recently for radiotherapy or CT are either based upon polyethylene (Kalender and Suess 1987, Kalender et al 1988, Hermann et al 1983, 1986 or epoxy resins (White et al 1977, Goodsitt et al 1991, Süß and Kalender 1996. The demand for special materials mimicking selected tissues typically requires the production of a small number of phantom samples.…”