Verification of image quality improvement of low-count bone scintigraphy using deep learning.

To improve image quality for low-count bone scintigraphy using deep learning and evaluate their clinical applicability. Six hundred patients (training, 500; validation, 50; evaluation, 50) were included in this study. Low-count original images (75%, 50%, 25%, 10%, and 5% counts) were generated from reference images (100% counts) using Poisson resampling. Output (DL-filtered) images were obtained after training with U-Net using reference images as teacher data. Gaussian-filtered images were generated for comparison. Peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) to the reference image were calculated to determine image quality. Artificial neural network (ANN) value, bone scan index (BSI), and number of hotspots (Hs) were computed using BONENAVI analysis to assess diagnostic performance. Accuracy of bone metastasis detection and area under the curve (AUC) were calculated. PSNR and SSIM for DL-filtered images were highest in all count percentages. BONENAVI analysis values for DL-filtered images did not differ significantly, regardless of the presence or absence of bone metastases. BONENAVI analysis values for original and Gaussian-filtered images differed significantly at ≦25% counts in patients without bone metastases. In patients with bone metastases, BSI and Hs for original and Gaussian-filtered images differed significantly at ≦10% counts, whereas ANN values did not. The accuracy of bone metastasis detection was highest for DL-filtered images in all count percentages; the AUC did not differ significantly. The deep learning method improved image quality and bone metastasis detection accuracy for low-count bone scintigraphy, suggesting its clinical applicability.

The citrus flavonoid, nobiletin inhibits neuronal inflammation by preventing the activation of NF-κB.

Nobiletin (5,6,7,8,3',4'-hexamethoxyflavone) is one of the flavonoids found in shikuwasa, a popular citrus fruit in Okinawa, Japan. It exerts various pharmacological effects, such as anti-tumor, antioxidant, and anti-inflammatory activities. We herein investigated whether nobiletin attenuated lipopolysaccharide (LPS)-induced inflammatory responses in the murine microglial cell line BV-2 and neuroinflammation in mice induced by an intracerebral injection of LPS. In BV-2 cells, nobiletin significantly inhibited the LPS-induced production of nitric oxide (NO) and prostaglandin E2 (PGE2) by preventing the mRNA expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively. Nobiletin also inhibited the LPS-induced mRNA expression of CCL2, CXCL1, IL-6, and TNFα. Nobiletin markedly attenuated the transcriptional activity of the NF-κB p65 subunit without affecting the degradation of IκBα or the nuclear localization of the NF-κB p65 subunit. Nobiletin also inhibited the LPS-induced activation of JNK, but not ERK or p38, in BV-2 cells. Furthermore, the administration of nobiletin significantly suppressed the accumulation of microglia and induction of the mRNA expression of CCL2, CXCL1, IL-6, and TNFα in the murine brain induced by injecting LPS into the striatum. Collectively, these results suggest the potential of nobiletin as a candidate anti-inflammatory drug for the prevention of neuroinflammation.

Relationship Between Patient-Friendly Audiovisual Systems and MRI Contrast Agent to Adverse Reactions.

BACKGROUND: Patient-friendly audiovisual (AV) systems in head MRI examinations can potentially reduce patient anxiety and contrast-enhanced MRI (CE-MRI) adverse reactions to gadolinium. PURPOSE: To evaluate whether a patient-friendly AV system reduces the rate of adverse reactions to gadolinium-based contrast agents. STUDY TYPE: Retrospective. POPULATION: Four thousand eight hundred thirty-two outpatients (2462 female) attending for clinical CE-MRI studies. (Gadoteridol: 1971, Meglumine gadoterate: 2733, Gadobutrol: 128.) FIELD STRENGTH/SEQUENCE: Routine CE-MRI of head and neck using a 1.5 T or 3 T scanner with or without a patient-friendly AV system. ASSESSMENT: One thousand one hundred fifty-nine patients were scanned on MRI machines equipped with patient-friendly AV systems (AV group) and 3673 on MRI machines without AV systems (control group). Adverse reaction rate and symptoms were reviewed by referring to the system database and electronic medical records and compared between the two groups. Adverse reactions were defined as physiological reactions, such as vomiting and allergic-like reactions, such as urticaria, occurring within 1 hour of contrast injection. We compare patient backgrounds, adverse reaction rate, adverse reactions symptoms and the severity between the two groups. STATISTICAL TESTS: Adverse reaction rate with and without a patient-friendly AV system were compared using Fisher's exact test. The relationship between patient-friendly AV systems and the occurrence of adverse reactions was evaluated with logistic regression. Statistical significance was set at P < 0.05. RESULTS: Of the 4832 patients enrolled, 65 (1.35%) experienced adverse reactions. The most common adverse reactions in both groups were urticaria and pruritus. Adverse reaction rate was significantly lower in the AV group than in the control group (0.7% vs. 1.6%). No significant difference was observed in the severity (P = 1.000) of adverse reactions and symptoms (allergic-like reaction: P = 0.08, physiologic reaction: P = 1.000) between the two groups. DATA CONCLUSION: The patient-friendly AV system significantly reduce adverse reaction occurrence to gadolinium-based contrast agents. EVIDENCE LEVEL: 4 TECHNICAL EFFICACY: Stage 1.

Optimization of the Attenuation Coefficient for Chang Attenuation Correction in 123I Brain Perfusion SPECT.

N-isopropyl-p-123I-iodoamphetamine brain perfusion SPECT has been used with various attenuation coefficients (µ-values); however, optimization is required. This study aimed to determine the optimal µ-value (µopt-value) for Chang attenuation correction (AC) using clinical data by comparing the Chang method and CT-based AC. Methods: We used 100 patients (reference group, 60; disease group, 40) who underwent N-isopropyl-p-123I-iodoamphetamine SPECT. SPECT images of the reference group were obtained to calculate the AC using the Chang method (µ-values, 0.07-0.20; 0.005 interval) and the CT-based method, both without scatter correction (SC) and with SC. The µopt-value with the smallest mean percentage error for the brain regions of the reference group was calculated. Agreement between the Chang and CT-based methods applying the µopt-value was evaluated using Bland-Altman analysis. Additionally, the percentage error in the region of hypoperfusion in the diseased group was compared with the percentage error in the same region in the reference group when the µopt-value was applied. Results: The µopt-values were 0.140 for Chang without SC and 0.160 for Chang with SC. In the Chang method, with the µopt-value applied, fixed and proportional biases were observed in the Bland-Altman analysis (both P < 0.05), and there was a tendency for the percentage error to be underestimated in the limbic regions and overestimated in the central brain regions. There was no significant difference between the disease group and the reference group in the region of hypoperfusion in either Chang without SC or Chang with SC. Conclusion: The present study revealed that the µopt-values of the Chang method are 0.140 without SC and 0.160 with SC.

Suppression of Neuroinflammation by Coffee Component Pyrocatechol via Inhibition of NF-κB in Microglia.

According to numerous studies, it has been epidemiologically suggested that habitual coffee intake seems to prevent the onset of neurodegenerative diseases. In this study, we hypothesized that coffee consumption suppresses neuroinflammation, which is closely related to the development of neurodegenerative diseases. Using microglial BV-2 cells, we first found that the inflammatory responses induced by lipopolysaccharide (LPS) stimulation was diminished by both coffee and decaffeinated coffee through the inhibition of an inflammation-related transcription factor, nuclear factor-κB (NF-κB). Pyrocatechol, a component of roasted coffee produced by the thermal decomposition of chlorogenic acid, also exhibited anti-inflammatory activity by inhibiting the LPS-induced activation of NF-κB. Finally, in an inflammation model using mice injected with LPS into the cerebrum, we observed that intake of pyrocatechol as well as coffee decoctions drastically suppressed the accumulation of microglia and the expression of interleukin-6 (IL-6), tumor necrosis factor α (TNFα), CCL2, and CXCL1 in the inflammatory brain. These observations strongly encourage us to hypothesize that the anti-inflammatory activity of pyrocatechol as well as coffee decoction would be useful for the suppression of neurodegeneration and the prevention of the onsets of Alzheimer's (AD) and Perkinson's diseases (PD).

Determination of a reliable assessment for occupational eye lens dose in nuclear medicine.

The most recent statement published by the International Commission on Radiological Protection describes a reduction in the maximum allowable occupational eye lens dose from 150 to 20 mSv/year (averaged over 5-year periods). Exposing the eye lens to radiation is a concern for nuclear medicine staff who handle radionuclide tracers with various levels of photon energy. This study aimed to define the optimal dosimeter and means of measuring the amount of exposure to which the eye lens is exposed during a routine nuclear medicine practice. A RANDO human phantom attached to Glass Badge and Luminess Badge for body or neck, DOSIRIS and VISION for eyes, and nanoDot for body, neck, and eyes was exposed to 99m Tc, 123 I, and 18 F radionuclides. Sealed syringe sources of each radionuclide were positioned 30 cm from the abdomen of the phantom. Estimated exposure based on measurement conditions (i.e., air kerma rate constants, conversion coefficient, distance, activity, and exposure time) was compared measured dose equivalent of each dosimeter. Differences in body, neck, and eye lens dosimeters were statistically analyzed. The 10-mm dose equivalent significantly differed between the Glass Badge and Luminess Badge for the neck, but these were almost equivalent at the body. The 0.07-mm dose equivalent for the nanoDot dosimeters was greatly overestimated compared to the estimated exposure of 99m Tc and 123 I radionuclides. Measured dose equivalents of exposure significantly differed between the body and eye lens dosimeters with respect to 18 F. Although accurately measuring radiation exposure to the eye lenses of nuclear medicine staff is conventionally monitored using dosimeters worn on the chest or abdomen, eye lens dosimeters that provide a 3-mm dose equivalent near the eye would be a more reliable means of assessing radiation doses in the mixed radiation environment of nuclear medicine.

Development of attenuation correction methods using deep learning in brain-perfusion single-photon emission computed tomography.

PURPOSE: Computed tomography (CT)-based attenuation correction (CTAC) in single-photon emission computed tomography (SPECT) is highly accurate, but it requires hybrid SPECT/CT instruments and additional radiation exposure. To obtain attenuation correction (AC) without the need for additional CT images, a deep learning method was used to generate pseudo-CT images has previously been reported, but it is limited because of cross-modality transformation, resulting in misalignment and modality-specific artifacts. This study aimed to develop a deep learning-based approach using non-attenuation-corrected (NAC) images and CTAC-based images for training to yield AC images in brain-perfusion SPECT. This study also investigated whether the proposed approach is superior to conventional Chang's AC (ChangAC). METHODS: In total, 236 patients who underwent brain-perfusion SPECT were randomly divided into two groups: the training group (189 patients; 80%) and the test group (47 patients; 20%). Two models were constructed using Autoencoder (AutoencoderAC) and U-Net (U-NetAC), respectively. ChangAC, AutoencoderAC, and U-NetAC approaches were compared with CTAC using qualitative analysis (visual evaluation) and quantitative analysis (normalized mean squared error [NMSE] and the percentage error in each brain region). Statistical analyses were performed using the Wilcoxon signed-rank sum test and Bland-Altman analysis. RESULTS: U-NetAC had the highest visual evaluation score. The NMSE results for the U-NetAC were the lowest, followed by AutoencoderAC and ChangAC (P < 0.001). Bland-Altman analysis showed a fixed bias for ChangAC and AutoencoderAC and a proportional bias for ChangAC. ChangAC underestimated counts by 30-40% in all brain regions. AutoencoderAC and U-NetAC produced mean errors of <1% and maximum errors of 3%, respectively. CONCLUSION: New deep learning-based AC methods for AutoencoderAC and U-NetAC were developed. Their accuracy was higher than that obtained by ChangAC. U-NetAC exhibited higher qualitative and quantitative accuracy than AutoencoderAC. We generated highly accurate AC images directly from NAC images without the need for intermediate pseudo-CT images. To verify our models' generalizability, external validation is required.

[Accuracy of Standardized Uptake Values Obtained by Quantitative PET/CT and SPECT/CT].

Quantification of PET/CT and SPECT/CT using standardized uptake value (SUV) is affected by many factors related to technical factors, such as scanner calibration, imaging physics related factors and patient related factors. Here, I briefly describe some world trend in accuracy of SUVs in PET/CT and SPECT/CT, followed by present and future strategies for clinical practice using SUVs. Finally, I also provided the results of multi-center phantom studies in Japan using SUVs of PET/CT and SPECT/CT.

Multicenter study of quantitative PET system harmonization using NIST-traceable 68Ge/68Ga cross-calibration kit.

PURPOSE: The present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable 68Ge/68Ga source as the reference standard. METHODS: We used 68Ge/68Ga dose calibrator and PET sources made with same batch of 68Ge/68Ga embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable 68Ge/68Ga sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site. RESULTS: The average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was -4.94% and -12.22%, respectively, before, and -0.14% and -4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by -4.70% under optimal conditions. CONCLUSION: Our proposed method using an NIST-traceable 68Ge/68Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies.

Optimization of a shorter variable-acquisition time for legs to achieve true whole-body PET/CT images.

The present study aimed to qualitatively and quantitatively evaluate PET images as a function of acquisition time for various leg sizes, and to optimize a shorter variable-acquisition time protocol for legs to achieve better qualitative and quantitative accuracy of true whole-body PET/CT images. The diameters of legs to be modeled as phantoms were defined based on data derived from 53 patients. This study analyzed PET images of a NEMA phantom and three plastic bottle phantoms (diameter, 5.68, 8.54 and 10.7 cm) that simulated the human body and legs, respectively. The phantoms comprised two spheres (diameters, 10 and 17 mm) containing fluorine-18 fluorodeoxyglucose solution with sphere-to-background ratios of 4 at a background radioactivity level of 2.65 kBq/mL. All PET data were reconstructed with acquisition times ranging from 10 to 180, and 1200 s. We visually evaluated image quality and determined the coefficient of variance (CV) of the background, contrast and the quantitative %error of the hot spheres, and then determined two shorter variable-acquisition protocols for legs. Lesion detectability and quantitative accuracy determined based on maximum standardized uptake values (SUVmax) in PET images of a patient using the proposed protocols were also evaluated. A larger phantom and a shorter acquisition time resulted in increased background noise on images and decreased the contrast in hot spheres. A visual score of ≥ 1.5 was obtained when the acquisition time was ≥ 30 s for three leg phantoms, and ≥ 120 s for the NEMA phantom. The quantitative %errors of the 10- and 17-mm spheres in the leg phantoms were ± 15 and ± 10%, respectively, in PET images with a high CV (scan < 30 s). The mean SUVmax of three lesions using the current fixed-acquisition and two proposed variable-acquisition time protocols in the clinical study were 3.1, 3.1 and 3.2, respectively, which did not significantly differ. Leg acquisition time per bed position of even 30-90 s allows axial equalization, uniform image noise and a maximum ± 15% quantitative accuracy for the smallest lesion. The overall acquisition time was reduced by 23-42% using the proposed shorter variable than the current fixed-acquisition time for imaging legs, indicating that this is a useful and practical protocol for routine qualitative and quantitative PET/CT assessment in the clinical setting.

Comparison of 3 Devices for Automated Infusion of Positron-Emitting Radiotracers.

The administration accuracy and precision of an automated infusion device for positron-emitting radiotracers are directly associated with bias and variance in the SUVs of 18F-FDG PET/CT. Therefore, the accuracy of such devices must be confirmed and calibrated at locations in which they are used. The present study aimed to validate the administration accuracy of 3 automated infusion devices for quantitative PET assessment. Methods: Temporal variations as well as variations in radioactive concentrations and dispensed volumes of 18F-FDG were determined for the M-130, AI-300, and UG-05 automated infusion devices. The total-test dispensed volumes were 25, 20, and 18.5 mL, respectively. A reference value was generated by measuring amounts of radioactivity using a standard dose calibrator. Administration accuracy was validated according to the criteria of the Japanese Society of Nuclear Medicine. Results: The temporal variation in the M-130 and UG-05 for a specified 185 MBq was relatively stable, in the range of -1.60%-0.92% and 1.16%-5.35%, respectively, whereas that in the AI-300 was -0.55%-8.68%. For the M-130 and UG-05 devices, the difference between measured and reference value was in the range of -5%-5%. The values measured by the AI-300 deviated from the reference values by a maximum of 30%, which depends on radioactive concentration and dispensed volume of 18F-FDG. Conclusion: The administration accuracy of the AI-300 varied considerably under different conditions, but a software update might somewhat improve this. Our findings indicate that dispensed volumes of 18F-FDG should be carefully considered when the radioactive concentration is high. Administration accuracy should be regularly confirmed at each location to maintain the quality of quantitative PET assessment. The present study provides useful information about how to confirm the administration accuracy of automated infusion devices.

Evaluation of spatial dependence of point spread function-based PET reconstruction using a traceable point-like 22Na source.

BACKGROUND: The point spread function (PSF) of positron emission tomography (PET) depends on the position across the field of view (FOV). Reconstruction based on PSF improves spatial resolution and quantitative accuracy. The present study aimed to quantify the effects of PSF correction as a function of the position of a traceable point-like 22Na source over the FOV on two PET scanners with a different detector design. METHODS: We used Discovery 600 and Discovery 710 (GE Healthcare) PET scanners and traceable point-like 22Na sources (<1 MBq) with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons. The source was moved in three directions at intervals of 1 cm from the center towards the peripheral FOV using a three-dimensional (3D)-positioning robot, and data were acquired over a period of 2 min per point. The PET data were reconstructed by filtered back projection (FBP), the ordered subset expectation maximization (OSEM), OSEM + PSF, and OSEM + PSF + time-of-flight (TOF). Full width at half maximum (FWHM) was determined according to the NEMA method, and total counts in regions of interest (ROI) for each reconstruction were quantified. RESULTS: The radial FWHM of FBP and OSEM increased towards the peripheral FOV, whereas PSF-based reconstruction recovered the FWHM at all points in the FOV of both scanners. The radial FWHM for PSF was 30-50 % lower than that of OSEM at the center of the FOV. The accuracy of PSF correction was independent of detector design. Quantitative values were stable across the FOV in all reconstruction methods. The effect of TOF on spatial resolution and quantitation accuracy was less noticeable. CONCLUSIONS: The traceable 22Na point-like source allowed the evaluation of spatial resolution and quantitative accuracy across the FOV using different reconstruction methods and scanners. PSF-based reconstruction reduces dependence of the spatial resolution on the position. The quantitative accuracy over the entire FOV of the PET system is good, regardless of the reconstruction methods, although it depends slightly on the position.

Evaluation of scatter limitation correction: a new method of correcting photopenic artifacts caused by patient motion during whole-body PET/CT imaging.

OBJECTIVE: Overcorrection of scatter caused by patient motion during whole-body PET/computed tomography (CT) imaging can induce the appearance of photopenic artifacts in the PET images. The present study aimed to quantify the accuracy of scatter limitation correction (SLC) for eliminating photopenic artifacts. METHODS: This study analyzed photopenic artifacts in (18)F-fluorodeoxyglucose ((18)F-FDG) PET/CT images acquired from 12 patients and from a National Electrical Manufacturers Association phantom with two peripheral plastic bottles that simulated the human body and arms, respectively. The phantom comprised a sphere (diameter, 10 or 37 mm) containing fluorine-18 solutions with target-to-background ratios of 2, 4, and 8. The plastic bottles were moved 10 cm posteriorly between CT and PET acquisitions. All PET data were reconstructed using model-based scatter correction (SC), no scatter correction (NSC), and SLC, and the presence or absence of artifacts on the PET images was visually evaluated. The SC and SLC images were also semiquantitatively evaluated using standardized uptake values (SUVs). RESULTS: Photopenic artifacts were not recognizable in any NSC and SLC image from all 12 patients in the clinical study. The SUVmax of mismatched SLC PET/CT images were almost equal to those of matched SC and SLC PET/CT images. Applying NSC and SLC substantially eliminated the photopenic artifacts on SC PET images in the phantom study. SLC improved the activity concentration of the sphere for all target-to-background ratios. The highest %errors of the 10 and 37-mm spheres were 93.3 and 58.3%, respectively, for mismatched SC, and 73.2 and 22.0%, respectively, for mismatched SLC. CONCLUSION: Photopenic artifacts caused by SC error induced by CT and PET image misalignment were corrected using SLC, indicating that this method is useful and practical for clinical qualitative and quantitative PET/CT assessment.

Evaluation of a revised version of computer-assisted diagnosis system, BONENAVI version 2.1.7, for bone scintigraphy in cancer patients.

OBJECTIVE: BONENAVI is a computer-assisted diagnosis system that analyzes bone scintigraphy automatically. We experienced more than a few segmentation errors with the previous BONENAVI version (2.0.5). We have since obtained a revised version (2.1.7) and evaluate it. METHODS: Bone scans of patients were analyzed by BONENAVI version 2.0.5 and a revised version 2.1.7 with regard to segmentation errors, sensitivity, and specificity. Patients with skeletal metastases from prostate cancer, lung cancer, breast cancer, and other cancers were included in the study as true-positive cases. Patients with no skeletal metastasis (regardless of hot spots), and patients with abnormal bone scans but no skeletal metastasis were included as negative cases. Bone-scan patients were subjected to artificial neural network (ANN) evaluation. Values equal to or above 0.5 were regarded as positive, and those below 0.5 as negative. The patients whose clinical status did not correspond to their ANN scores were assessed for any similarities. RESULTS: The frequency of segmentation errors was statistically significantly reduced when using BONENAVI version 2.1.7. The differences in sensitivity and specificity for the results of version 2.0.5 versus version 2.1.7 were not different, giving a high Cohen's kappa coefficient. In the patients who showed an increased ANN value with version 2.1.7, a few false-positive thoracic lesions were identified. Patients whose ANN value was significantly high with version 2.0.5 showed no tendencies. CONCLUSION: Revised BONENAVI version 2.1.7 for bone scintigraphy was superior with regard to segmentation errors. However, its sensitivity and specificity were similar to those of version 2.0.5. The false-positive identification of thoracic lesions in revised version 2.1.7 might be subject to remedy.

Evaluation of a computer-assisted diagnosis system, BONENAVI version 2, for bone scintigraphy in cancer patients in a routine clinical setting.

OBJECTIVE: To evaluate a computer-assisted diagnosis system, BONEVAVI version 2 for bone scintigraphy, this study examined the performance of the software in patients with and without skeletal metastasis. METHODS: Bone scans of various patients were analyzed by BONENAVI version 2. Patients with skeletal metastasis from prostate cancer, lung cancer, breast cancer, and other cancers were included in the study as true positive cases. Patients with normal bone scans, consecutive patients with several days of no skeletal metastasis (regardless of hot spots), and patients with abnormal bone scans but no skeletal metastasis were included as negative cases. Patient artificial neural network (ANN) values equal to or above 0.5 were regarded as positive, and those below 0.5 as negative. This study also analyzed cases according to primary cancer factors, osseous metastasis type, and bone tumor burden. RESULTS: The sensitivity of patient ANN values was 121/142 (85 %) for all cancers, 25/29 (86 %) for prostate cancer, 35/40 (88 %) for lung cancer, 37/45 (82 %) for breast cancer, and 24/28 (86 %) for other cancers. The specificity of ANN values was 40/49 (82 %) for normal bone scans, 99/122 (81 %) for consecutive patients with several days of no skeletal metastasis, and 44/81 (54 %) for patients with abnormal bone scans but no skeletal metastasis. Patients showing false negatives included: 10 patients with small lesions (6 of whom showed positive lesion ANN values), 4 patients with osteolytic lesions, 5 patients with intertrabecular osseous metastasis, and 1 patient with a metastatic lesion adjacent to the urinary bladder. The correlation between manually counted lesion numbers and Bone Scan Index was excellent for prostate cancer, and was good for lung cancer, breast cancer, and other cancers. CONCLUSION: BONENAVI version 2 is an effective computer-assisted diagnosis system for bone scanning, but the drawbacks of bone scanning remain unresolved.

[Technical Approaches for Quantitative Treatment Responses Using 18F-FDG PET].

Quantitative assessment of 18F-FDG PET can predict treatment responses or outcomes. Here, I briefly describe some world trends in standardizing PET images for image-based assessments of treatment responses, followed by present and future strategies for defining the optimal acquisition conditions for quantitative PET imaging. Finally, information is provided about new technical approaches to improving the quantitation of semi-quantitative indexes such as point spread function, time-of-flight and respiratory gating.

[Improvement of quantitative accuracy using phase-based respiratory-gated PET/CT in phantom and clinical studies].

OBJECTIVE: The present study aimed at determining the quantitative accuracy of phase-based respiratory-gated PET/CT imaging using phantom and clinical studies. METHODS: The effects of target size, target-to-background ratio (TBR), and respiratory motion on PET images were estimated using a NEMA body phantom comprising six spheres (diameter 10-37mm) in a solution of F-18 of three different TBRs (4, 6, 8). The phantom was moved in a superior-inferior direction at motion displacements of 0, 10, 20 and 30 mm. Stationary images of the phantom as well as non-gated (3D) and gated (4D) images of the phantom while moving were reconstructed and the recovery coefficient (RC) of individual spheres was calculated from each image. We then determined the RC improvement rate to evaluate improvements conferred by 4D-PET/CT. We retrospectively analyzed data from 14 patients with lung cancer who were examined by 3D- and 4D-PET/CT. Each lesion on the 3D-PET/CT and each of the five phases of the 4D-PET/CT were analyzed. RESULTS: Larger motion displacement and TBR resulted in increased RC degradation for small spheres. The RC improvement rate showed that 4D acquisition improved the RC of spheres with larger motion displacement exceeding 13 mm in diameter. 4D-PET/CT alone can reduce the effects of motion blurring, but partial volume effects may still be the dominant source of quantitative inaccuracy for small lesions. The trends of phantom and clinical studies for evaluating the improvement rate were similar. CONCLUSIONS: 4D-PET/CT significantly improved the quantitative accuracy of PET images particularly when larger motion displacement exceeded 17mm in diameter such as in lung cancer.

Optimal radiation shielding for beta and bremsstrahlung radiation emitted by (89)Sr and (90)Y: validation by empirical approach and Monte Carlo simulations.

OBJECTIVE: High-energy beta emitters such as Strontium-89 ((89)Sr) and Yttrium-90 ((90)Y) are becoming increasingly popular nuclear therapy sources in Japan for treating cancer. Various characteristics of materials must be considered when designing radiation protection device for high-energy beta emitters. We empirically measured and simulated dose equivalents of beta and bremsstrahlung radiation arising from (89)Sr and (90)Y radiation shielded with various materials and determined optimal shielding materials against these sources. METHODS: The dose equivalents of (89)Sr and (90)Y determined experimentally using an ionization chamber survey meter were compared with those of Monte Carlo simulations. The relative dose equivalents of beta and bremsstrahlung radiation separately transmitted by changing the thickness of acrylic, aluminum, iron, lead and tungsten shielding materials were simulated. RESULTS: Dose equivalents were consistent between the empirical measurements and the simulation to within ±5%. Shielding ability was more effective in the order of tungsten, lead, iron, aluminum and acrylic against both (89)Sr and (90)Y. The amount of beta and bremsstrahlung radiation transmitted through tungsten and lead was relatively small. Although such high-density material generates much bremsstrahlung radiation, it absorbs the bremsstrahlung radiations. CONCLUSIONS: Tungsten was the optimal material for efficient shielding against (89)Sr and (90)Y radiation and preferable among operators. The present findings provide useful information about how to define an appropriate shielding strategy for high-energy beta emitters.