Interpolated average CT for cardiac PET/CT attenuation correction

Mok, Greta S. P.; Ho, Cobie Y.T.; Yang, Bohan; Wu, Tung Hsin

doi:10.1007/s12350-015-0140-5

Cited by 11 publications

(6 citation statements)

References 26 publications

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“…Voluntary and involuntary mismatch errors not only cause artifacts in the SPECT data due to the use of misaligned CT for AC [11,12], but also misleading anatomical localization for later segmentation required for dosimetric calculations. He et al have studied the impact of SPECT/planar and CT misregistration at the same imaging time point and mis-definition of volume-of-interest (VOI) from manual segmentation on activity estimation [13].…”

Section: Introductionmentioning

confidence: 99%

The Effects of Mismatch between SPECT and CT Images on Quantitative Activity Estimation – A Simulation Study

Lyu

Chen

Mok

2021

Preprint

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Background: Quantitative activity estimation is essential in targeted radionuclide therapy dosimetry. Misregistration between SPECT and CT images at the same imaging time point due to patient movement degrades accuracy. This work aims to study the mismatch effects between CT and SPECT data on attenuation correction (AC), volume-of-interest (VOI) delineation and registration for activity estimation.Methods: Nine 4D XCAT phantoms were generated at 1, 24, and 144 hrs post In-111 Zevalin injection, varying in activity distributions, body and organ sizes. Realistic noisy SPECT projections were generated by an analytical projection and reconstructed with quantitative OS-EM method. CT images were shifted from -5 to 5 voxels as well as according to clinical reference corresponding to SPECT images at each time point. For AC effect, mismatched CT images were used for AC in SPECT reconstruction while VOIs were mapped out from matched CTs. For VOI effect, target organs were mapped out using mismatched CTs with matched CTs for AC. For registration effect, non-rigid registrations were performed on sequential mismatched CTs to align corresponding SPECT images, with no AC and VOI mismatch. Bi-exponential curve fitting was performed to obtain time-integrated activity (TIA). Organ activity errors (%OAE) and TIA errors (%TIAE) were calculated.Results: According to clinical reference, %OAE was larger for organs near ribs for AC effect, e.g., -2.58%±0.81% for liver. For VOI effect, %OAE was larger for small and low uptake organs, e.g., -11.94%±10.34% for spleen. %OAE was proportional to mismatch magnitude, e.g., 4.77%±1.41%, 12.01%±3.97% and 42.81%±6.38% for 1-, 2-, and 5-voxel mismatch for lungs. For registration effect, %TIAE were larger when mismatch existed in more numbers of SPECT/CT images, while no substantial difference was observed when using mismatched CT at different time points for registration reference. %TIAE was highest for VOI, followed by registration and AC, e.g., 37.61%±5.08%, 14.25%±7.07% and 1.13%±0.90% respectively for kidneys.Conclusions: The mismatch between CT and SPECT images poses a significant impact on accuracy of quantitative activity estimation in dosimetry, attributed particularly from VOI delineation errors. It is recommended to perform registration between emission and transmission images at the same time point to ensure dosimetric accuracy.

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Section: Introductionmentioning

confidence: 99%

The Effects of Mismatch between SPECT and CT Images on Quantitative Activity Estimation – A Simulation Study

Lyu

Chen

Mok

2021

Preprint

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“…Attenuation correction (AC) can be performed by estimating the tissue ACFs distribution, known as AC maps. Hybrid PET and Computed Tomography (CT) systems allow the estimation of highly-accurate CT-based AC (CT-AC) maps for superior PET quantification (4,5). Nevertheless, PET/CT detectability may be limited for some lesions due to CT's low soft-tissue contrast (6).…”

Section: Introductionmentioning

confidence: 99%

Hybrid PET- and MR-driven attenuation correction for enhanced 18F-NaF and 18F-FDG quantification in cardiovascular PET/MR imaging

Karakatsanis

Abgral

Trivieri

et al. 2020

Journal of Nuclear Cardiology

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Background: The standard MR Dixon-based attenuation correction (AC) method in Positron Emission Tomography / Magnetic Resonance (PET/MR) imaging segments only the air, lung, fat and soft-tissues (4-class), thus neglecting the highly attenuating bone tissues and affecting quantification in bones and adjacent vessels. We sought to address this limitation by utilizing the distinctively high bone uptake rate constant Ki expected from 18 F-Sodium Fluoride (18 F-NaF) to segment bones from PET data and support 5-class hybrid PET/MR-driven AC for 18 F-NaF and 18 F-Fluorodeoxyglucose (18 F-FDG) PET/MR cardiovascular imaging. Methods: We introduce 5-class Ki/MR-AC for (i) 18 F-NaF studies where the bones are segmented from Patlak Ki images and added as the 5 th tissue class to the MR-Dixon 4-class AC map. Furthermore, we propose two alternative dual-tracer protocols to permit 5-class Ki/MR-AC for (ii) 18 F-FDG-only data, with a streamlined simultaneous administration of 18 F-FDG and 18 F-NaF at 4:1 ratio (R4:1), or (iii) for 18 F-FDG-only or both 18 F-FDG and 18 F-NaF dual-tracer data, by administering 18 F-NaF 90 min after an equal 18 F-FDG dosage (R1:1). The Ki-driven bone segmentation was validated against Computed Tomography (CT)-based segmentation in rabbits, followed by PET/MR validation on 108 vertebral bone and carotid wall regions in 16 human volunteers with and without prior indication of carotid atherosclerosis disease (CAD). Results: In rabbits, we observed similar (<1.2% mean difference) vertebral bone 18 F-NaF SUVmean scores when applying 5-class AC with Ki-segmented bone (5-class Ki/CT-AC) versus CT-segmented bone (5-class CT-AC) tissue. Considering the PET data corrected with continuous CT-AC maps as gold-standard, the percentage SUVmean bias was reduced by 17.6% (18 F-NaF) and 15.4% (R4:1) with 5-class Ki/CT-AC versus 4-class CT-AC. In humans without prior CAD indication, we reported 17.7% and 20% higher 18 F-NaF target-to-background ratio (TBR) at carotid bifurcations wall and vertebral bones, respectively, with 5-versus 4-class AC. In the R4:1 human cohort, the mean 18 F-FDG TBR increased by 12.2% at carotid bifurcations wall and 19.9% at vertebral bones. For the R1:1 cohort of human without CAD indication, mean TBR increased by 15.3% (18 F-FDG) and 15.5% (18 F-NaF) at carotid bifurcations and 21.6% (18 F-FDG) and 22.5% (18 F-NaF) at vertebral bones. Similar TBR enhancements were observed whe applying the proposed AC method to human subjects with prior CAD indication.. Conclusions: Ki-driven bone segmentation and 5-class hybrid PET/MR-driven AC is feasible and can significantly enhance 18 F-NaF and 18 F-FDG contrast and quantification in bone tissues and carotid walls.

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“…That would potentially degrade the 99m Tc-MAA SPECT/CT quantitative accuracy, affecting the LSF and TNR calculation. The use of average CT, including cine average CT (CACT) and our previously proposed interpolated average CT (IACT), has been proven to be an effective AC method to reduce the respiratory artifacts and improve the quantification for thoracic SPECT [11] and PET [13][14][15]. Besides, segmentation of lungs, liver and tumors also highly affects the dosimetric accuracy for 99m Tc-MAA SPECT/CT [16].…”

Section: Introductionmentioning

confidence: 99%

CT Protocols for Attenuation Correction and Segmentation in 99mTc-MAA SPECT/CT for 90Y Radioembolization Treatment Planning – a Simulation Study

Lü¹,

Mok²

2020

Preprint

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Background Conventional 99mTc-macroaggregated albumin (99mTc-MAA) planar scintigraphy overestimates lung shunt fraction (LSF) as compared to SPECT/CT in 90Y radioembolization treatment planning. However, the respiratory motion artifact due to the temporal mismatch between static SPECT and helical CT (HCT) may compromise the SPECT quantitation accuracy by incorrect attenuation correction (AC) and volume-of-interest segmentation. The goal of this study is to systematically assess different AC and segmentation protocols for LSF, tumor-to-normal liver (TNR), organ absorbed dose and injected activity (IA) estimation in 99mTc-MAA SPECT/CT.Methods The 4D XCAT phantom was used to simulate 10 patient anatomies with 99mTc-MAA distribution based on the clinical data, each with LSF of 5%, 10%, 15% and 20%, axial respiratory motion of 2 cm, different TNR and tumor size. An analytical projector for low energy high resolution parallel-hole collimator was used to simulate realistic noisy planar acquisitions, and 128 projections over 360o for SPECT, both modeling attenuation, scatter and geometric collimator-detector-response. Five attenuation maps, i.e., (i) HCT at end-inspiration (HCT-IN), (ii) HCT at mid-respiration (HCT-MID), (iii) HCT at end-expiration (HCT-EX), (iv) cine averaged CT (CACT) and (v) interpolated average CT (IACT) were applied for SPECT AC and segmentation in LSF, dosimetric and IA evaluation. Mid-respiratory phases were also extracted from CACT/IACT for VOI segmentation while CACT/IACT were used for AC, i.e., hybrid CT protocols.Results For LSF estimation, SPECT/CACT has the least absolute errors. Planar significantly overestimates LSF and lung absorbed dose compared to SPECT especially for LSF of 5%. SPECT-based is better than CT-based segmentation in TNR estimation. There is no statistically significant difference for different CT protocols for TNR, normal liver and tumor absorbed dose estimation. Hybrid CTs and HCT-MID performed the best for IA especially for higher LSF.Conclusions 99mTc-MAA SPECT/CT with an appropriate choice of CT protocol for AC and segmentation is superior to planar in LSF and lung absorbed dose estimation. The 4D CT protocols are recommended for AC and segmentation to alleviate respiratory artifacts and improve quantitation accuracy in 90Y radioembolization treatment planning. HCT-EX would also be a recommended choice if 4D CT is not available.

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Interpolated average CT for cardiac PET/CT attenuation correction

Abstract: IACT-AC reduced respiratory artifacts and improved PET/CT matching similarly to ACT-AC. It is a promising low-dose alternate of ACT for cardiac PET/CT.

Cited by 11 publications

References 26 publications

The Effects of Mismatch between SPECT and CT Images on Quantitative Activity Estimation – A Simulation Study

The Effects of Mismatch between SPECT and CT Images on Quantitative Activity Estimation – A Simulation Study

Hybrid PET- and MR-driven attenuation correction for enhanced 18F-NaF and 18F-FDG quantification in cardiovascular PET/MR imaging

CT Protocols for Attenuation Correction and Segmentation in 99mTc-MAA SPECT/CT for 90Y Radioembolization Treatment Planning – a Simulation Study

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