Tomographic 99mTc radioactivity quantification in three-dimensional printed polymeric phantoms with bioinspired geometries

3D printed anthropomorphic left ventricular myocardial phantom for nuclear medicine imaging applications

Background

Anthropomorphic torso phantoms, including a cardiac insert, are frequently used to investigate the imaging performance of SPECT and PET systems. These phantom solutions are generally featuring a simple anatomical representation of the heart. 3D printing technology paves the way to create cardiac phantoms with more complex volume definition. This study aimed to describe how a fillable left ventricular myocardium (LVm) phantom can be manufactured using geometry extracted from a patient image.

Methods

The LVm of a healthy subject was segmented from ¹⁸F-FDG attenuation corrected PET image set. Two types of phantoms were created and 3D printed using polyethylene terephthalate glycol (PETG) material: one representing the original healthy LVm, and the other mimicking myocardium with a perfusion defect. The accuracy of the LVm phantom production was investigated by high-resolution CT scanning of 3 identical replicas. ^99mTc SPECT acquisitions using local cardiac protocol were performed, without additional scattering media (“in air” measurements) for both phantom types. Furthermore, the healthy LVm phantom was inserted in the commercially available DataSpectrum Anthropomorphic Torso Phantom (“in torso” measurement) and measured with hot background and hot liver insert.

Results

Phantoms were easy to fill without any air-bubbles or leakage, were found to be reproducible and fully compatible with the torso phantom. Seventeen segments polar map analysis of the "in air” measurements revealed that a significant deficit in the distribution appeared where it was expected. 59% of polar map segments had less than 5% deviation for the "in torso” and "in air” measurement comparison. Excluding the deficit area, neither comparison had more than a 12.4% deviation. All the three polar maps showed similar apex and apical region values for all configurations.

Conclusions

Fillable anthropomorphic 3D printed phantom of LVm can be produced with high precision and reproducibility. The 3D printed LVm phantoms were found to be suitable for SPECT image quality tests during different imaging scenarios. The flexibility of the 3D printing process presented in this study provides scalable and anthropomorphic image quality phantoms in nuclear cardiology imaging.

[99mTc]Tc-iPSMA SPECT brain imaging as a potential specific diagnosis of metastatic brain tumors and high-grade gliomas

BACKGROUND

PSMA (prostate-specific membrane antigen) protein is heavily expressed in the proliferating microvasculature of high-grade gliomas (HGG) and brain metastases (BM). This research aimed to assess [99mTc]Tc-iPSMA SPECT brain imaging as a potential specific diagnosis of HGG and BM by PSMA-targeting in their proliferating vasculature.

METHODS

Forty-one patients, with suspected brain tumors, as detected by enhanced MRI scanning, were enrolled to undergo preoperative [99mTc]Tc-iPSMA SPECT brain imaging. Semiquantitative image analyses, to evaluate the maximum target-to-background ratio (TBRmax), were performed. All diagnoses were histopathologically confirmed. PSMA expression was evaluated by immunohistochemistry (IHC) in 11 brain tumor tissues. TBRmax values were correlated with IHC results and tumor WHO grade (HGG vs LGG).

RESULTS

[99mTc]Tc-iPSMA images showed increased uptake in BM, HGG, and recurrent gliomas (TBRmax of 25.1 ± 7.1, 18.5 ± 9.0, 15.0 ± 9.9, respectively), and was negative in treatment-naive patients with LGG and reactive gliosis. PSMA was highly expressed in the vascular endothelium of grade IV gliomas and BM, while its expression was extremely low in LGG and completely absent in gliosis. By using 2.8 as a threshold value for TBRmax, the specificity, sensitivity, PPV, NPV and accuracy were 100%, 94%, 100%, 77% and 95%, respectively.

CONCLUSIONS

The results of this pilot study show that [99mTc]Tc-iPSMA SPECT brain imaging is a specific and potentially useful neuroimaging tool for assessing tumoral neovasculature formation in gliomas and brain metastases.