title: New head equivalent phantom for task and image performance evaluation representative for neurovascular procedures occurring in the Circle of Willis.
abstract: Phantom equivalents of different human anatomical parts are routinely used for imaging system evaluation or dose calculations. The various recommendations on the generic phantom structure given by organizations such as the AAPM, are not always accurate when evaluating a very specific task. When we compared the AAPM head phantom containing 3 mm of aluminum to actual neuro-endovascular image guided interventions (neuro-EIGI) occurring in the Circle of Willis, we found that the system automatic exposure rate control (AERC) significantly underestimated the x-ray parameter selection. To build a more accurate phantom for neuro-EIGI, we reevaluated the amount of aluminum which must be included in the phantom. Human skulls were imaged at different angles, using various angiographic exposures, at kV's relevant to neuro-angiography. An aluminum step wedge was also imaged under identical conditions, and a correlation between the gray values of the imaged skulls and those of the aluminum step thicknesses was established. The average equivalent aluminum thickness for the skull samples for frontal projections in the Circle of Willis region was found to be about 13 mm. The results showed no significant changes in the average equivalent aluminum thickness with kV or mAs variation. When a uniform phantom using 13 mm aluminum and 15 cm acrylic was compared with an anthropomorphic head phantom the x-ray parameters selected by the AERC system were practically identical. These new findings indicate that for this specific task, the amount of aluminum included in the head equivalent must be increased substantially from 3 mm to a value of 13 mm.
authors.affiliation: University at Buffalo (State University of New York), Toshiba Stroke Research Center, 3435 Main St., Buffalo, NY 14214, USA.
authors.forename: Ciprian N
authors.initials: CN
authors.lastname: Ionita
authors.forename: Brendan
authors.initials: B
authors.lastname: Loughran
authors.forename: Amit
authors.initials: A
authors.lastname: Jain
authors.forename: S N
authors.initials: SN
authors.lastname: Swetadri Vasan
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Bednarek
authors.forename: Elad
authors.initials: E
authors.lastname: Levy
authors.forename: Adnan H
authors.initials: AH
authors.lastname: Siddiqui
authors.forename: Kenneth V
authors.initials: KV
authors.lastname: Snyder
authors.forename: L N
authors.initials: LN
authors.lastname: Hopkins
authors.forename: Stephen
authors.initials: S
authors.lastname: Rudin
keywords: Circle of Willis; Head equivalent phantom; digital subtracted angiography; fluoroscopy; uniform phantom
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