浅田 恭生

BACKGROUND: Cardiac amyloidosis requires quantitative assessment using technetium-99m pyrophosphate (99mTc-PYP) single-photon emission computed tomography (SPECT)/computed tomography (CT) for adequate discrimination and evaluation of disease extent. This study aimed to evaluate the utility of standardized uptake value (SUV) analysis using 99mTc-PYP SPECT/CT in pathologically-confirmed transthyretin amyloid cardiomyopathy (ATTR-CM). The study also explored the relationship between local uptake heterogeneity and indicators of cardiac impairment. METHODS: Forty patients diagnosed via heart biopsy and genetic analysis (20 ATTR-CM; 4 light-chain amyloidosis, 16 non-amyloidosis) were enrolled. The mean SUVs of the heart and aorta were measured using SPECT images. Discrimination performance was evaluated by comparing each SUV, the heart-to-aorta ratio (rSUVH/Ao), and the heart-to-contralateral-lung ratio with pathological findings serving as the gold standard. Polar maps were analyzed to assess local SUV distribution in patients with ATTR-CM. The coefficient of variation (COV) of myocardial uptake, difference score between the septum and lateral wall (%DS), base-to-apex variability, and total cardiac SUV were calculated and compared with echocardiographic parameters. RESULTS: All metrics were significantly different between the ATTR-CM and non-amyloidosis groups. The rSUVH/Ao effectively differentiated patients with ATTR-CM from those with light-chain or non-amyloidosis. Local myocardial SUV distribution correlated with impaired cardiac function. Notably, COV showed significant correlations with e' (R = 0.782) and E/e' (R =  - 0.625), linking heterogeneity to myocardial stiffness and diastolic dysfunction. Larger %DS, which predominantly reflected the ATTR-CM pattern of high septal uptake, correlated significantly with thinner walls (average wall thickness, R =  - 0.655; relative wall thickness, R =  - 0.486). As the total cardiac SUV increased, the %DS decreased (reflecting more homogeneous distribution), and global longitudinal strain worsened (R = 0.614). These observations indicated that greater impairment was associated with a higher disease burden. CONCLUSIONS: This study demonstrated that quantitative SPECT analysis provides a valuable tool for the diagnostic evaluation and differentiation of ATTR-CM. The rSUVH/Ao offers high discriminatory performance. Local heterogeneity and total myocardial uptake are closely related to the disease burden and extent, as reflected by structural and functional abnormalities on echocardiography. These findings suggest potential relevance to the non-invasive assessment of these aspects of the disease at a single time point.

PURPOSE: The computed tomography (CT) numbers of key organs and biological structures are important for phantom production. This study aimed to provide basic data on the CT numbers of actual organs, including the placenta, amniotic fluid, fetal bones, and fetal organs. Additionally, the abdominal circumference of pregnant women and skin surface-to-fetus distance were measured. METHODS: Maternal and fetal anatomical data were obtained from the imaging data of 14 pregnant patients who had previously undergone abdominal and pelvic CT examinations. All anatomical measurements were performed on a workstation using the CT images of each patient. The imaging data of the 14 pregnant patients did not include repeated data from the same individuals. RESULTS: For each organ, the average CT numbers did not significantly differ across tube voltage or gestational age groups. The average CT numbers of the fetal brain, lungs, liver, and caput femoris were 22.2, 28.9, 55.3, and 504.9 HU, respectively. The average values for the fetal depth and maternal abdominal circumference were 28.0 and 861.5 mm, respectively. CONCLUSIONS: The CT numbers of the placenta, amniotic fluid, and fetal organs are similar to those of adult soft tissues and should be represented by equivalent materials. However, the fetal lung phantom should not be made of the same material used for adult lung phantoms; instead, it should consist of materials simulating soft tissue. Because the position of the fetus varies among individuals, determining the measurement point inside the phantom requires a customizable design, particularly for pregnant women with minimal subcutaneous fat.

Anthropomorphic phantoms are often used to estimate organ absorbed doses. However, the material composition of these phantoms is not identical to that of the human body, which may cause errors in the measurement results. The purpose of this study was to analyze the material composition of several anthropomorphic torso phantoms using dual energy computed tomography (DECT), and to clarify the differences in attenuation characteristics among the phantoms. Anthropomorphic torso phantoms (ATOM, RANDO, and PBU-60) from different manufacturers were scanned with DECT. The target organs were lung, soft tissue, liver, bone, and bone surface, and a spectral Hounsfield unit curve (HU curve) was created from the relationship between energy and CT values. Ideal CT values were estimated from the mass attenuation coefficient and density proposed by the International Commission on Radiation Units and Measurements report 44 (ideal value) and compared with the values of each phantom. There were large differences in attenuation characteristics among the phantoms for soft tissue, liver, and bone. The respective ideal, ATOM, RANDO, and PBU-60 CT values of soft tissue were 59.82, 14.17, 34.22, and - 70.11 at 45 keV; and 53.13, 24.41, 3.97, and - 5.75 at 70 keV. The phantom closest to the ideal value may differ depending on the energy. Differences in HU curve and CT values indicate that some organs in the phantom have different material composition and attenuation characteristics to human tissues. When the phantoms available for dosimetry are limited, it is important to understand the attenuation characteristics of each phantom used.

When exposed to X-rays, scintillators emit visible luminescence. X-ray-mediated optogenetics employs scintillators for remotely activating light-sensitive proteins in biological tissue through X-ray irradiation. This approach offers advantages over traditional optogenetics, allowing for deeper tissue penetration and wireless control. Here, we assessed the short-term safety and efficacy of candidate scintillator materials for neuronal control. Our analyses revealed that lead-free halide scintillators, such as Cs3Cu2I5, exhibited significant cytotoxicity within 24 h and induced neuroinflammatory effects when injected into the mouse brain. In contrast, cerium-doped gadolinium aluminum gallium garnet (Ce:GAGG) nanoparticles showed no detectable cytotoxicity within the same period, and injection into the mouse brain did not lead to observable neuroinflammation over four weeks. Electrophysiological recordings in the cerebral cortex of awake mice showed that X-ray-induced radioluminescence from Ce:GAGG nanoparticles reliably activated 45% of the neuronal population surrounding the implanted particles, a significantly higher activation rate than europium-doped GAGG (Eu:GAGG) microparticles, which activated only 10% of neurons. Furthermore, we established the cell-type specificity of this technique by using Ce:GAGG nanoparticles to selectively stimulate midbrain dopamine neurons. This technique was applied to freely behaving mice, allowing for wireless modulation of place preference behavior mediated by midbrain dopamine neurons. These findings highlight the unique suitability of Ce:GAGG nanoparticles for X-ray-mediated optogenetics. The deep tissue penetration, short-term safety, wireless neuronal control, and cell-type specificity of this system offer exciting possibilities for diverse neuroscience applications and therapeutic interventions.

This study aimed to assess fetal radiation exposure in pregnant women undergoing computed tomography (CT) and rotational angiography (RA) examinations for the diagnosis of pelvic trauma. In addition, this study aimed to compare the dose distributions between the two examinations. Surface and average fetal doses were estimated during CT and RA examinations using a pregnant phantom model and real-time dosemeters. The pregnant model phantom was constructed using an anthropomorphic phantom, and a custom-made abdominal phantom was used to simulate pregnancy. The total average fetal dose received by pregnant women from both CT scans (plain, arterial and equilibrium phases) and a single RA examination was ~60 mGy. Because unnecessary repetition of radiographic examinations, such as CT or conventional 2D angiography can increase the radiation risk, the irradiation range should be limited, if necessary, to reduce overall radiation exposure.