A moving liver phantom in an anthropomorphic thorax for SPECT MP imaging

Cranio-caudal respiratory motion and liver activity cause a variety of complex myocardial perfusion (MP) artifacts, especially in the inferior myocardial wall, that may also mask cardiac defects. To assess and characterise such artifacts, an anthropomorphic thorax with moving thoracic phantoms can be utilised in SPECT MP imaging. In this study, a liver phantom was developed and anatomically added into an anthropomorphic phantom that also encloses an ECG beating cardiac phantom and breathing lungs’ phantom. A cranio-caudal respiratory motion was also developed for the liver phantom and it was synchronised with the corresponding ones of the other thoracic phantoms. This continuous motion was further divided into isochronous dynamic respiratory phases, from end-exhalation to end-inspiration, to perform SPECT acquisitions in different respiratory phases. The new motions’ parameters and settings were measured by mechanical means and also validated in a clinical environment by acquiring CT images and by using two imaging software packages. To demonstrate the new imaging capabilities of the phantom assembly, SPECT/CT MP acquisitions were performed and compared to previous phantom and patients studies. All thoracic phantoms can precisely perform physiological motions within the anthropomorphic thorax. The new capabilities of the phantom assembly allow to perform SPECT/CT MP acquisitions for different cardiac-liver activity ratios and cardiac-liver proximities in supine and, for first time, in prone position. Thus, MP artifacts can be characterised and motion correction can be performed due to these new capabilities. The impact of artifacts and motion correction on defect detection can be also investigated.

An optimized imaging protocol for [99mTc]Tc-DPD scintigraphy and SPECT/CT quantification in cardiac transthyretin (ATTR) amyloidosis

Background In [99mTc]Tc-DPD scintigraphy for myocardial ATTR amyloidosis, planar images 3 hour p.i. and SPECT/CT acquisition in L-mode are recommended. This study investigated if earlier planar images (1 hour p.i.) are beneficial and if SPECT/CT acquisition should be preferred in H-mode (180° detector angle) or L-mode (90°). Methods In SPECT/CT phantom measurements (NaI cameras, N = 2; CZT, N = 1), peak contrast recovery (CRpeak) was derived from sphere inserts or myocardial insert (cardiac phantom; signal-to-background ratio [SBR], 10:1 or 5:1). In 25 positive and 38 negative patients (reference: endomyocardial biopsy or clinical diagnosis), Perugini scores and heart-to-contralateral (H/CL) count ratios were derived from planar images 1 hour and 3 hour p.i. Results In phantom measurements, accuracy of myocardial CRpeak at SBR 10:1 (H-mode, 0.95-0.99) and reproducibility at 5:1 (H-mode, 1.02-1.14) was comparable for H-mode and L-mode. However, L-mode showed higher variability of background counts and sphere CRpeak throughout the field of view than H-mode. In patients, sensitivity/specificity were ≥ 95% for H/CL ratios at both time points and visual scoring 3 hour. At 1 hour, visual scores showed specificity of 89% and reduced reader’s confidence. Conclusions Early DPD images provided no additional value for visual scoring or H/CL ratios. In SPECT/CT, H-mode is preferred over L-mode, especially if quantification is applied apart from the myocardium.

Rebuild-up Effect on Superficial Cardiac Lesion Surrounded by Low-density Lungs: Volumetric Modulated Arc Therapy (VMAT) Planning Study Using 3-D Printed Phantom for Ventricular Tachycardia (VT)

The study aimed to evaluate dose distributions on the superficial cardiac lesion surrounded by low-density lungs. We fabricated the 3-D printed cardiac phantom to insert in a multipurpose lungman phantom (KYOTO KAGAKU, Japan) for simulating a stereotactic body radiation therapy (SBRT) in ventricular tachycardia (VT) treatment. The cardiac phantom consists of 11 slabs with 1-cm intervals and is designed to insert radiochromic film (Gafchromic EBT3, Ashland Advanced Materials, Bridgewater, NJ) for film dosimetry. We used film dosimetry scanners (DosimetryPRO Advantage Red, Vidar Systems Corporation, Herndon, VA) with dedicated film dosimetry software (OP-IMRT, ver.1.6, IBA dosimetry, Germany). Volumetric modulated arc therapy (VMAT) technique was applied to optimize the dose distribution using the anisotropic analytic algorithm (AAA) in a radiation treatment planning (RTP) system (Eclipse v. 13.6, Varian, Palo Alto, CA). We used the 6-MV and 15-MV photon energies from a LINAC (Clinac iX, Varian, Palo Alto, CA) to investigate the planning target volume (PTV) under-dose effects due to the inner dose rebuild-up by energy dependence. The dose distributions in the VMAT plans with 6-MV and 15-MV showed good competitive coverages of the cardiac lesion without any severe underdose pattern. On the other side, the film dosimetry results showed significant dose variations near the interface of the cardiac lesion surrounded by low-density lung. The differences between the planning and the film dosimetry results revealed pretty well in both photon energies. The maximum dose differences in the cardiac PTV were ranged from 4.1–7.7% and 4.1–8.1% for 6-MV photon beams and 15-MV photon beams. Furthermore, EBT3 film measurements showed that the widths of 50% of profiles were reduced by 1.3 cm and 2.3 cm on 6-MV photon beams and 15-MV photon beams, respectively. In addition, 3-D printing techniques enabled quite challengeable dose measurements to reveal this kind of dose discrepancies in humanoid structures. This study showed that clinical cases like VT SBRT surrounded by severe inhomogeneous matter could induce wrongly to estimate appropriate dose delivery and to evaluate reasonable clinical outcomes.

A Moving Liver Phantom in An Anthropomorphic Thorax for SPECT MP Imaging

Cranio-caudal respiratory motion and liver activity cause a variety of complex myocardial perfusion (MP) artifacts, especially in the inferior myocardial wall, that may also mask cardiac defects. To assess and characterize such artifacts, an anthropomorphic thorax with moving thoracic phantoms can be utilized in SPECT MP imaging. In this study, a liver phantom was developed, and anatomically added into an anthropomorphic phantom, that encloses an ECG beating cardiac phantom and breathing lungs phantom. A cranio-caudal respiratory motion was also developed for the liver phantom and it was synchronized with the corresponding ones of the cardiac and lungs phantoms. This continuous motion could also be further divided into dynamic respiratory phases, from end-exhalation to end-inspiration, to perform SPECT acquisitions in different respiratory phases. The motion parameters, displacements and volumes, were validated by the acquired CT slices, the OsiriX and Vitrea software. Sample SPECT/16-slice-CT myocardial MP acquisitions were also performed and compared to the literature. The cardiac, lungs and liver phantoms can precisely perform, in time interval of 0.1 sec, physiological thoracic motions within an anthropomorphic thorax. This dynamic phantom assembly can be utilized for SPECT MP supine and, for first time, prone imaging to access and characterize artifacts due to different cranio-caudal respiratory amplitudes and cardiac-liver activity ratios.