Multimodal phantoms for clinical PET/MRI

Abstract

Phantoms are commonly used throughout medical imaging and medical physics for a multitude of applications, the designs of which vary between modalities and clinical or research requirements. Within positron emission tomography (PET) and nuclear medicine, phantoms have a well-established role in the validation of imaging protocols so as to reduce the administration of radioisotope to volunteers. Similarly, phantoms are used within magnetic resonance imaging (MRI) to perform quality assurance on clinical scanners, and gel-based phantoms have a longstanding use within the MRI research community as tissue equivalent phantoms. In recent years, combined PET/MRI scanners for simultaneous acquisition have entered both research and clinical use. This review explores the designs and applications of phantom work within the field of simultaneous acquisition PET/MRI as published over the period of a decade. Common themes in the design, manufacture and materials used within phantoms are identified and the solutions they provided to research in PET/MRI are summarised. Finally, the challenges remaining in creating multimodal phantoms for use with simultaneous acquisition PET/MRI are discussed. No phantoms currently exist commercially that have been designed and optimised for simultaneous PET/MRI acquisition. Subsequently, commercially available PET and nuclear medicine phantoms are often utilised, with CT-based attenuation maps substituted for MR-based attenuation maps due to the lack of MR visibility in phantom housing. Tissue equivalent and anthropomorphic phantoms are often developed by research groups in-house and provide customisable alternatives to overcome barriers such as MR-based attenuation correction, or to address specific areas of study such as motion correction. Further work to characterise materials and manufacture methods used in phantom design would facilitate the ability to reproduce phantoms across sites.

Methodological Advances in Studying Postnatal Locomotor Development

“…The ideal object to calibrate an unknown femur would thus be an identical femur of known mass distribution (which is actually attempted in clinical tomography, cf. Lennie et al, 2021).…”

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“…They noted that regional differences between PET/MR and PET/CT systems were minimized using CT-AC. Because white matter of the 3D brain phantom is composed of polymer, which is not visible in MR-AC, the Iida phantom is still insufficient for evaluation of MR-AC accuracy [ 100 ].…”

“…In human PET/MR studies, however, MR-AC is generally used to reconstruct PET images. A PET/MR multimodal phantom, which mimics the electron density and MR contrast of human tissue, is required to evaluate MR-AC accuracy, and facilitate PET/MR harmonization [ 100 ]. Harries et al [ 101 ] developed a realistic phantom of the human head using water-saturated gypsum plaster, silicone, agarose gel, etc.…”

Silicone‐based materials with tailored MR relaxation characteristics for use in reduced coil visibility and in tissue‐mimicking phantom design

“…Multi-modality phantoms, such as MRI-CT, positron emission tomography (PET)-MRI, and MR/ultrasound (US), are also in high demand. [22][23][24][25] For example, Singhrao et al developed an anthropomorphic pelvic daily quality assurance (DQA) phantom for MRI-CT radiotherapy testing. 25 Yunker et al 26 developed a 2portal vein flow phantom for imaging with US, MRI, and CT. Niebuhr et al 27 developed an anthropomorphic, deformable, and multimodal (ADAM) phantom for MRguided radiotherapy (MRgRT) with deformable organs for imaging on CT and MRI.…”

“…Multi‐modality phantoms, such as MRI‐CT, positron emission tomography (PET)‐MRI, and MR/ultrasound (US), are also in high demand 22–25 . For example, Singhrao et al.…”