A realistic phantom of the human head for PET-MRI

Johanna Harries,Tina Schlender,Bernhard Sattler,Henryk Barthel,Thomas Scholz,Thies H Jochimsen,Osama Sabri

doi:10.1186/s40658-020-00320-z

Abstract

BackgroundThe combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a unique hybrid imaging modality mainly used in oncology and neurology. The MRI-based attenuation correction (MRAC) is crucial for correct quantification of PET data. A suitable phantom to validate quantitative results in PET-MRI is currently missing. In particular, the correction of attenuation due to bone is usually not verified by commonly available phantoms. The aim of this work was, thus, the development of such a phantom and to explore whether such a phantom might be used to validate MRACs.MethodVarious materials were investigated for their attenuation and MR properties. For the substitution of bone, water-saturated gypsum plaster was used. The attenuation of 511 keV annihilation photons was regulated by addition of iodine. Adipose tissue was imitated by silicone and brain tissue by agarose gel, respectively. The practicability with respect to the comparison of MRACs was checked as follows: A small flask inserted into the phantom and a large spherical phantom (serving as a reference with negligible error in MRAC) were filled with the very same activity concentration. The activity concentration was measured and compared using clinical protocols on PET-MRI and different built-in and offline MRACs. The same measurements were carried out using PET-CT for comparison.ResultsThe phantom imitates the human head in sufficient detail. All tissue types including bone were detected as such so that the phantom-based comparison of the quantification accuracy of PET-MRI was possible. Quantitatively, the activity concentration in the brain, which was determined using different MRACs, showed a deviation of about 5% on average and a maximum deviation of 11% compared to the spherical phantom. For PET-CT, the deviation was 5%.ConclusionsThe comparatively small error in quantification indicates that it is possible to construct a brain PET-MRI phantom that leads to MR-based attenuation-corrected images with reasonable accuracy.

Highlights

The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a unique hybrid imaging modality mainly used in oncology and neurology
The comparatively small error in quantification indicates that it is possible to construct a brain PET-MRI phantom that leads to MR-based attenuation-corrected images with reasonable accuracy
The current study presents a head-shaped phantom made of different materials imitating MRI- and PET-specific properties of tissue in the human head

Summary

Introduction

The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a unique hybrid imaging modality mainly used in oncology and neurology. The aim of this work was, the development of such a phantom and to explore whether such a phantom might be used to validate MRACs. The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a very promising hybrid imaging technique which combines the high soft tissue contrast of MRI with the high functional sensitivity of PET [1]. MRI, on the other hand, is based on measuring the magnetization of the atomic nuclei. These two tissue properties are not directly related to each other [1]. For MRAC, several methods are available that provide routine AC (cf. Table 1)

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