Development and Application of Stable Phantoms for the Evaluation of Photoacoustic Imaging Instruments

Abstract

Photoacoustic imaging combines the high contrast of optical imaging with the spatial resolution and penetration depth of ultrasound. This technique holds tremendous potential for imaging in small animals and importantly, is clinically translatable. At present, there is no accepted standard physical phantom that can be used to provide routine quality control and performance evaluation of photoacoustic imaging instruments. With the growing popularity of the technique and the advent of several commercial small animal imaging systems, it is important to develop a strategy for assessment of such instruments. Here, we developed a protocol for fabrication of physical phantoms for photoacoustic imaging from polyvinyl chloride plastisol (PVCP). Using this material, we designed and constructed a range of phantoms by tuning the optical properties of the background matrix and embedding spherical absorbing targets of the same material at different depths. We created specific designs to enable: routine quality control; the testing of robustness of photoacoustic signals as a function of background; and the evaluation of the maximum imaging depth available. Furthermore, we demonstrated that we could, for the first time, evaluate two small animal photoacoustic imaging systems with distinctly different light delivery, ultrasound imaging geometries and center frequencies, using stable physical phantoms and directly compare the results from both systems.

Biologically relevant photoacoustic imaging phantoms with tunable optical and acoustic properties

“…After fusion, PVCP is poured into mold cavities to cool and solidify into arbitrary shapes. PVCP has been investigated as a material for photoacoustic phantoms, [37][38][39][40][41][42] and solid PVCP inclusions within background PVCP matrix have been reported stable for at least six months, 38 suggesting that this material is suitable for fabricating highly robust phantoms with stable properties. The PVCP formulation reported in the literature is a commercial product for making soft fishing lures (M-F Manufacturing Co., Inc., Fort Worth, Texas).…”

“…We performed acoustic characterization of 13 liquid plasticizers (Table 2), using methods described in Sec. 2.3, in order to identify 37,38 In this study we also chose to utilize these additives. Optical scattering affects the penetration depth of PAT, while optical absorption can be used to increase background optical attenuation or to fabricate absorptive inclusions within the phantom.…”

“…At this point, BPC and/or glass microspheres may be added and stirred in for 5 min. PVCP formulations were heated following the method described by Bohndiek et al 38 Briefly, PVCP was poured into a 100 mL round bottom flask in a magnetically-stirred oil bath maintained at 190°C using a thermocouple. The flask, which contained a stir bar, was then evacuated and stirred at ∼300 rpm.…”

Photoacoustic Imaging in Oncology: Translational Preclinical and Early Clinical Experience

“…These systems are mainly geared toward research and often provide custom image processing software that allows users to perform a multitude of tasks ranging from importing raw data for offline processing, to onboard three-dimensional image reconstruction, and real-time image display. Currently, there are two commercially available preclinical photoacoustic imaging systems as shown in Figure 3: Vevo LAZR (Fujifilm VisualSonics, Toronto, Canada; technology licensed from Seno Medical Instruments, San Antonio, Tex) and Nexus 128 (Endra, Ann Arbor, Mich; technology licensed from OptoSonics, Oriental, NC) (7,(44)(45)(46)(47)(48)(49). Vevo LAZR uses high-frequency where tissue with lower oxygen saturation is considered more likely to be cancerous due to cancer's known hypoxic nature in later stages (27,28).…”

Sulfates as chromophores for multiwavelength photoacoustic imaging phantoms

“…Part of the challenge is the access to suitable chromophores and phantoms for proof-of-concept, testing, validation, and optimization. Despite recent advances on the study of phantom matrix materials for general photoacoustic (PA) system characterization and quality control, [8][9][10][11][12] for multiwavelength and quantitative PAI purposes further efforts are needed, with one of the crucial issues being finding suitable chromophores. 13,14 It is essential for these to be well-characterized, well-behaved, and stable.…”