Impact of patient characteristic factors on the dynamics of liver glucose metabolism: Evaluation of multiparametric imaging with dynamic whole-body 18 F-fluorodeoxyglucose-positron emission tomography.

AIMS: To assess the impact of various patient characteristics on the dynamics of liver glucose metabolism using automated multiparametric imaging with whole-body dynamic 18 F-fluorodeoxyglucose (FDG)-positron emission tomography (PET). MATERIALS AND METHODS: We retrospectively enrolled 540 patients who underwent whole-body dynamic FDG-PET. Three quantitative indices representing hepatic glucose metabolism [mean standardized uptake value normalized by lean body mass (SULmean), metabolic glucose rate (kinetic index) and distribution volume (DV)] were measured from multiparametric PET images produced automatically based on the Patlak plot model. Patient characteristics including age, sex, body mass index, fasting time, blood glucose level, and the presence of diabetes mellitus (DM) or hepatic steatosis (HS) were collected. We examined the correlations between the characteristic factors and three quantitative indices using multiple regression analysis. RESULTS: The success rate of kinetic analysis using multiparametric PET imaging was 93.3% (504/540). Hepatic SULmean was significantly correlated with age (p < .001), sex (p < .001) and blood glucose level (p = .002). DV was significantly correlated with age (p = .033), sex (p < .001), body mass index (p = .002), fasting time (p = .043) and the presence of HS (p = .002). The kinetic index was significantly correlated with age (p < .001) and sex (p = .004). In the comparison of the healthy, DM and HS groups, patients with DM had a significantly increased SULmean, whereas patients with HS had a significantly decreased DV. CONCLUSIONS: Our results showed that liver glucose metabolism was influenced by various patient characteristic factors. Multiparametric FDG-PET imaging can be used to analyse the kinetics of liver glucose metabolism in routine clinical practice.

Impact of noise reduction on radiation dose reduction potential of virtual monochromatic spectral images: Comparison of phantom images with conventional 120 kVp images using deep learning image reconstruction and hybrid iterative reconstruction.

PURPOSE: To assess the effects of deep learning image reconstruction (DLIR) and hybrid iterative reconstruction (HIR) on the image quality of virtual monochromatic spectral (VMS) images and to investigate the dose reduction potential of the VMS and conventional 120 kVp images. METHODS: A cylindrical phantom simulating an adult abdomen was used. The contrast was set to 60 (medium) and 300 (high) Hounsfield units. CT acquisitions were performed at three dose levels: 12, 9, and 6 mGy. Images were reconstructed via filtered back projection (FBP), DLIR, and HIR. The noise power spectrum (NPS) and task transfer function (TTF) were measured, and the system performance (SP) function was calculated (TTF2/NPS). RESULTS: The noise magnitudes at low spatial frequencies with DLIR and HIR were lower than that with FBP by 45.6% and 24.4%, respectively. Compared to the FBP results, the TTF values at 50% with DLIR at medium and high contrast changed by -13.2% and +25.3% with the VMS images and -2.0% and +9.3% with the 120 kVp images, respectively. In the VMS and 120 kVp images, compared to the SP values of 12 mGy FBP images, SP values of 6 mGy DLIR images decreased at medium contrast and increased at high contrast. CONCLUSIONS: DLIR achieved better noise reduction than HIR. The spatial resolution of VMS-DLIR varied significantly depending on the contrast. The image quality of VMS-DLIR and 120 kVp-DLIR potentially decrease in medium contrast tasks and increase in high contrast tasks with 50% dose reduction.

Optimization of pediatric FDG-PET/CT examinations based on physical indicators using the SiPM-PET/CT system.

OBJECTIVE: This study aimed to investigate the appropriate Silicon photomultiplier -PET/CT acquisition and image reconstruction conditions for each age group. METHODS: The original phantom was developed to reflect the thickness and width of the torso in each age group (neonates, 1-year-olds, 5-year-olds, 10-year-olds, 15-year-olds, and adults). The ratio of hot spheres to background radioactivity was 4:1, and the radioactivity concentration was adjusted according to the Japanese consensus guidelines for appropriate implementation of pediatric nuclear medicine examinations. We evaluated the root mean square error (RMSE) as an assessment/function of the standardized uptake value of each hot sphere, the background variability (N10 mm), the % contrast of the hot sphere (QH, 10 mm/N10 mm), and the noise equivalent counts to determine the optimal reconstruction parameters and the appropriate acquisition time. RESULTS: The minimum RMSE was obtained by setting the half-width of the Gaussian filter to 0-2 mm for iteration 1 or 2 and to 2-4 mm for iteration 3 or more. The acquisition times that satisfied the image quality equivalent to 120 s acquisitions in the adult phantoms were 30 s in the neonatal and 1-year-old phantoms, 60 s in the 5- and 10-year-old phantoms, and 75 s in the 15-year-old phantoms. CONCLUSION: This study demonstrated that good PET images could be obtained with short acquisition times when the examination is performed under appropriate reconstruction conditions.

Egested Feces Revealed Massive Protein Loss in 99mTc-HSA-D Scintigraphy.

A 66-year-old man with severe diarrhea and severe hypoproteinemia was referred for Tc-DTPA-human serum albumin (HSA-D) scintigraphy. The scintigraphy at 24 hours postinjection showed strong accumulation of Tc-HSA-D in not only the colon but also all his diapers containing his egested feces. The ratio of the diapers counts to the total counts was 17.0%, and a considerable amount of protein loss was confirmed. Tc-HSA-D scintigraphy has an important role in diagnosing protein-losing enteropathy, but the abdomen is the only routinely scanned area. Additional scanning of egested radiotracer and the whole body can be useful for evaluating the disease severity.

Bone SPECT-based segmented attenuation correction for quantitative analysis of bone metastasis (B-SAC): comparison with CT-based attenuation correction.

BACKGROUND: Evidence has shown the clinical usefulness of measuring the metastatic tumor burden of bone for prognostic assessment especially in prostate cancer; quantitative evaluation by dedicated SPECT is difficult due to the lack of attenuation correction (AC) method. We developed a novel method for attenuation correction using bone SPECT emission data (bone SPECT-based segmented attenuation correction; B-SAC) where emission data were virtually segmented into three tissues (i.e., bone, soft tissue, and air). Then, the pixel values in SPECT were replaced by 50 for the virtual soft tissue, and - 1000 for the virtual air. The replaced pixel values for the virtual bone were based on the averaged CT values of the normal vertebrae (B-SACN) or the metastatic bones (B-SACM). Subsequently, the processed SPECT data (i.e., SPECT value) were supposed to realize CT data (i.e., CT value) that were used for B-SAC. The standardized uptake values (SUVs) of 112 metastatic bone tumors in 15 patients with prostate cancer were compared between CTAC with scatter correction (SC) and resolution recovery (RR) and the following reconstruction conditions: B-SACN (+)SC(+)RR(+), B-SACM (+)SC(+)RR(+), uniform AC(UAC)(+)SC(+)RR(+), AC(-)SC(+)RR(+), and no correction (NC). RESULTS: The SUVs in the five reconstruction conditions were all correlated with those in CTAC(+)SC(+)RR(+) (p < 0.01), and the correlations between B-SACN or B-SACM and CTAC images were excellent (r > 0.94). Bland-Altman analysis showed that the mean SUV differences between CTAC (+)SC(+)RR(+) and the other five reconstructions were 0.85 ± 2.25 for B-SACN (+)SC(+)RR(+), 1.61 ± 2.36 for B-SACM (+)SC(+)RR(+), 1.54 ± 3.84 for UAC(+)SC(+)RR(+), - 3.12 ± 4.97 for AC(-)SC(+)RR(+), and - 5.96 ± 4.59 for NC. Compared to CTAC(+)SC(+)RR(+), B-SACN (+)SC(+)RR(+) showed a slight but constant overestimation (approximately 17%) of the metastatic tumor burden of bone when the same threshold of metabolic tumor volume was used. CONCLUSIONS: The results of this preliminary study suggest the potential for B-SAC to improve the quantitation of bone metastases in bone SPECT when X-ray CT or transmission CT data are not available. Considering the small but unignorable differences of lesional SUVs between CTAC and B-SAC, SUVs obtained with the current version of B-SAC seem difficult to be directly compared with those obtained with CTAC.

Fatal Intracranial Hemorrhage Due to Thrombocytopenia in a Patient With Castration-Resistant Prostate Cancer Showing Extensive Bone Uptake of Injected 223Ra Dichloride.

A 64-year-old man with castration-resistant prostate cancer received Ra injection to treat bone metastases. The patient underwent a Ra SPECT scan after the first Ra injection in which there was increased uptake all over the spine. Spine-to-background activity ratio in the patient was approximately three times greater than normal spine-to-background activity ratios in Ra SPECT obtained from the other patients. Eight days after the fifth injection, the patient exhibited a very poor neurologic examination and died of intracranial hemorrhage due to severe thrombocytopenia (platelet counts, 23,000/mm). The extensive radiation to the spine may have enhanced myelophthisic process in this case.

Effects of breathing motion on PET acquisitions: step and shoot versus continuous bed motion.

OBJECTIVES: Continuous bed motion (CBM) acquisition recently became available in whole-body PET/CT scanners in addition to the conventional step and shoot (S&S) acquisition. In this work, we compared the image quality between these acquisition methods using a phantom simulating periodic motion to mimic motion from patient breathing in a controlled manner. METHODS: PET image quality was assessed using the National Electrical Manufacturers Association IQ torso phantom filled with an F-FDG solution using a 4 : 1 target-to-background ratio. The phantom was scanned in two states: no motion (stationary) and with periodic motion in the axial direction with a displacement ±10 mm from the initial position. Both S&S and CBM scans were repeated 10 times in an alternating order, whereby the acquisition duration of each scan was adjusted to make the true counts approximately comparable to compensate for the decaying F-FDG. RESULTS: The recovery coefficient analysis showed that in the stationary state, the 10 mm sphere recovery did not show any difference between S&S and CBM. With motion, the recovery coefficient was lower by ∼40% for both modes of acquisition. In addition, the image-based volume analysis of the 10 mm sphere showed 1.67 (1.57-1.69) cm for S&S and 1.73 (1.66-1.83) cm for CBM (P=0.13), and there was no difference between two modes. Our study indicated that when the acquisition conditions for S&S and CBM (equivalent net trues, identical phantom motion, and identical CT image used for PET corrections) were controlled carefully, these acquisition modes resulted in equivalent image quality.

High-Energy Collimator Is Preferable to Medium-Energy Collimator for Evaluating 223Ra Uptake in Bone Metastasis at 2 Weeks Postinjection.

An 80-year-old man with castration-resistant prostate cancer received Ra injection to treat bone metastases. Two weeks after the injection, the patient underwent static Ra scan of the chest with medium-energy and high-energy collimators for 30 minutes each. Images obtained with the 2 collimators showed that uptake in metastatic lesions was visually clearer and semiquantitatively higher with the high-energy collimator. The use of HE collimator for Ra imaging in the early phase has been reported, and the present case suggests that in the late phase HE collimator would also be preferable to medium-energy collimator in terms of lesion-based evaluation.

Ra-223 SPECT for semi-quantitative analysis in comparison with Tc-99m HMDP SPECT: phantom study and initial clinical experience.

BACKGROUND: Image-based measurement of absorbed dose of Ra-223 dichloride may be useful in predicting therapeutic outcome in patients with castration-resistant prostate cancer (CRPC). In general, SPECT has been found to be more accurate than planar imaging in terms of lesion-based analysis. The aims of this study were to assess the feasibility and clinical usefulness of Ra-223 SPECT. The energy spectrum of Ra-223 and SPECT images of a cylindrical phantom with a hot rod were obtained to determine the collimator candidates and energy window settings suitable for clinical Ra-223 SPECT (basic study A). Another phantom with a tube-shaped chamber and two spheres simulating bowel activity and metastatic lesions in the lumbar spine was scanned with medium-energy general-purpose (MEGP) and high-energy general-purpose (HEGP) collimators (basic study B). Ten patients with CRPC underwent SPECT imaging 2 h after Ra-223 injection successively with MEGP and HEGP collimators in random order for 30 min each. Lesion detectability and semi-quantitative analyses of bone metastasis (i.e. lesion-to-background ratio (LBR)) were performed compared to Tc-99m HMDP SPECT. RESULTS: Basic study A revealed that an 84-keV photopeak ± 20% using the HEGP collimator offers better SPECT image quality than the other imaging conditions. Basic study B showed that uptake in one of the spheres was overestimated by overlapped activity of the tube-shaped chamber in planar imaging whereas the spheres had similar counts and significantly higher sphere-to-background ratio in SPECT. On both planar and SPECT images, HEGP gave higher image contrast than MEGP (p < 0.01). In the clinical study, Ra-223 SPECT at 84 keV ± 20% depicted more lesions with the HEGP than with the MEGP collimator (51 vs 36, p = 0.013). There was a positive correlation between LBR in Tc-99m SPECT and in Ra-223 SPECT (r = 0.67 with the MEGP and 0.69 with the HEGP collimator, p < 0.01). LBRs were significantly higher with the HEGP than with the MEGP collimator (p < 0.01). CONCLUSIONS: We recommended the use of the HEGP collimator at 84 keV ± 20% for Ra-223 SPECT imaging. Lesion-based semi-quantitative analysis in the human study revealed a good correlation between Ra-223 and Tc-99m HMDP SPECT in the early phase (2-3 h post injection).

Use of a digital phantom developed by QIBA for harmonizing SUVs obtained from the state-of-the-art SPECT/CT systems: a multicenter study.

BACKGROUND: Although quantitative analysis using standardized uptake value (SUV) becomes realistic in clinical single-photon emission computed tomography/computed tomography (SPECT/CT) imaging, reconstruction parameter settings can deliver different quantitative results among different SPECT/CT systems. This study aims to propose a use of the digital reference object (DRO), which is a National Electrical Manufacturers Association (NEMA) phantom-like object developed by the Quantitative Imaging Biomarker Alliance (QIBA) fluorodeoxyglucose-positron emission tomography technical committee, for the purpose of harmonizing SUVs in Tc-99m SPECT/CT imaging. METHODS: The NEMA body phantom with determined Tc-99m concentration was scanned with the four state-of-the-art SPECT/CT systems. SPECT data were reconstructed using different numbers of the product of subset and iteration numbers (SI) and the width of 3D Gaussian filter (3DGF). The mean (SUVmean), maximal (SUVmax), and peak (SUVpeak) SUVs for six hot spheres (10, 13, 17, 22, 28, and 37 mm) were measured after converting SPECT count into SUV using Becquerel calibration factor. DRO smoothed by 3DGF with a FWHM of 17 mm (DRO17 mm) was generated, and the corresponding SUVs were measured. The reconstruction condition to yield the lowest root mean square error (RMSE) of SUVmeans for all the spheres between DRO17 mm and actual phantom images was determined as the harmonized condition for each SPECT/CT scanner. Then, inter-scanner variability in all quantitative metrics was measured before (i.e., according to the manufacturers' recommendation or the policies of their own departments) and after harmonization. RESULTS: RMSE was lowest in the following reconstruction conditions: SI of 100 and 3DGF of 13 mm for Brightview XCT, SI of 160 and 3DGF of 3 pixels for Discovery NM/CT, SI of 60 and 3DGF of 2 pixels for Infinia, and SI of 140 and 3DGF of 15 mm for Symbia. In pre-harmonized conditions, coefficient of variations (COVs) among the SPECT/CT systems were greater than 10% for all quantitative metrics in three of the spheres, SUVmax and SUVmean, in one of the spheres. In contrast, all metrics except SUVmax in the 17-mm sphere yielded less than 10% of COVs after harmonization. CONCLUSIONS: Our proposed method clearly reduced inter-scanner variability in SUVs. A digital phantom developed by QIBA would be useful for harmonizing SUVs in multicenter trials using SPECT/CT.

Characteristic X-ray imaging for palliative therapy using strontium-89 chloride: understanding the mechanism of nuclear medicine imaging of strontium-89 chloride.

Strontium-89 (Sr-89) chloride is a targeted palliative therapy used for painful bone metastasis in which repeated doses can be administered, and its usefulness has been reported in the case of bone metastasis of various primary tumors. However, the effectiveness of the pain relief treatment is only described using a subjective index such as the visual analog scale, which lacks objectivity. Although various attempts at quantifying the effectiveness of Sr-89 chloride therapy have been reported using nuclear medicine imaging for energy peaks around 70-80 keV, the principle of Sr-89 chloride imaging has not been explained. In this study, the principle of nuclear medicine imaging for Sr-89 chloride was evaluated using a fundamental study. Additionally, the optimal collimator for acquiring Sr-89 chloride image data was evaluated. Based on the results, the principle of nuclear medicine imaging for Sr-89 chloride could be explained: the energy peaks were characteristic X-rays produced by interactions between gamma rays (514 keV) emitted from Sr-85, which is included during the manufacturing process of the Sr-89 chloride solution, and the lead collimator used in the imaging. The optimal collimator for generating characteristic X-rays efficiently was identified as a middle-to-high energy collimator.