Trends and Progress in Neuroendovascular Treatment in Japan: Japanese Registry of Neuroendovascular Therapy (JR-NET) 4. Main Report.

We reported the main results of the Japanese Registry of Neuroendovascular Therapy (JR-NET) 4, a nationwide surveillance of therapy (NET) in Japan from January 2015 to December 2019. JR-NET 4 registered consecutive patients who underwent NETs by Japan Society of Neuroendovascular Therapy (JSNET) -certified specialists. The primary endpoint was functional independence (mRS score of 0-2) at 30 days post-NET, with secondary endpoints focusing on technical success and major adverse events within 30 days.A total of 63,230 patients and 60,354 NET procedures from 166 participating centers were analyzed. During the study period, NET cases have consistently increased, with an increase in the proportion of elderly patients. A significant trend shift was observed in the distribution of NET procedures, with endovascular treatment for acute ischemic stroke that showed a dramatic increase in 5 years. This trend aligns with key randomized clinical trials from 2015 that presented the efficacy of this treatment. Clinical outcomes at 30 days posttreatment revealed that endovascular treatment for acute ischemic stroke and other NETs maintained safety and effectiveness despite varying prevalence of functional independence between target diseases. The study also observed a steady increase in emergency treatment cases, reflecting the increase in acute ischemic stroke, a time-sensitive medical condition.This comprehensive surveillance highlights the trend of NET practices in Japan, driven by clinical evidence and advancements in treatment devices. Although these findings were specific to Japan, they offer valuable insights into the broader trends in NETs and acute stroke care.

Differences in mechanical thrombectomy for acute ischemic stroke on weekdays versus nights/ weekends in a Japanese primary stroke core center.

OBJECTIVE: The term "weekend effect" refers to an increase in the mortality rate for hospitalizations occurring on weekends versus weekdays. In this study, we investigated whether such an effect exists in patients undergoing mechanical thrombectomy for acute ischemic stroke with large vessel occlusion (currently the standard treatment for this condition) at a single center in Japan. METHODS: We surveyed 151 patients who underwent mechanical thrombectomy for acute ischemic stroke with large vessel occlusion (75 and 76 patients were treated during daytime and nighttime, respectively) from January 2019 to June 2021. The items evaluated in this analysis were the rate of modified Rankin Scale ≤2 or prestroke scale, mortality, and procedural treatment time. RESULTS: The rates of modified Rankin Scale ≤2 or prestroke scale and mortality at 90 days after treatment did not differ significantly between daytime and nighttime (41.3% vs. 29.0%, p=0.11; 14.7% vs. 11.8%, p=0.61, respectively). The door-to-groin time tended to be shorter during daytime versus nighttime (57 [IQR: 42.5-70] min vs. 70 [IQR: 55-82]) min, p=0.0507). CONCLUSIONS: This study did not reveal differences in treatment outcome between daytime and nighttime in patients undergoing mechanical thrombectomy for acute ischemic stroke with large vessel occlusion. Therefore, the "weekend effect" was not observed in our institution.

Time-of-flight magnetic resonance angiography for detection of postoperative recurrence in patients with chronic subdural hematoma.

PURPOSE: Chronic subdural hematoma (CSDH) is associated with postoperative recurrence. Although various factors are involved in postoperative recurrence of CSDH, blood flow, especially in the middle meningeal artery (MMA), is considered to play an important role. We investigated whether the degree of signal intensity (SI) of the MMA on time-of-flight magnetic resonance angiography (TOF MRA) and various clinical factors are involved in recurrence of CSDH. METHODS: The maximum SI of both MMAs was measured on TOF MRA images within 1 month before or after the initial surgery. RESULTS: In total, 185 patients (20 with and 165 without recurrence of CSDH) were included in the analysis. The SI ratio and dementia were significant predictors of recurrence of CSDH (SI ratio: odds ratio [95% confidence interval (CI)] = 1.71 [1.32, 2.22], p < 0.0001; dementia: odds ratio [95% CI] = 7.41 [1.83, 30.1], p = 0.005). The estimated regression coefficients in the final model were 6.14 for the SI ratio and 1.28 for dementia. The risk score was derived according to these regression coefficients as follows: score = 5 × SI ratio + 1 (dementia: yes). With a score of 5, the predicted probability of recurrence was 2% [95% CI 0.7, 5.7], whereas with scores of 8 and 10, the probability was 43.3% [27.0, 61.1] and 89.5% [65.7, 97.5], respectively, which increased the risk of recurrence. CONCLUSION: Patients with an increased SI ratio of the affected MMA on TOF MRA who underwent surgery for CSDH were significantly more likely to experience recurrence.

Safety of Apixaban Monotherapy for Non-Valvular Atrial Fibrillation-Related Acute Stroke with Intra-/Extracranial Artery Stenosis.

INTRODUCTION: We investigated whether apixaban is safe for the prevention of further adverse events in non-valvular atrial fibrillation (NVAF) patients with intra-/extracranial artery stenosis (Stenosis group) compared with acute large vessel occlusion without intra-/extracranial artery stenosis (No stenosis group). We also examined whether combination therapy using apixaban and antiplatelet is safe. METHODS: ALVO (Apixaban on clinical outcome of patients with Large Vessel Occlusion [LVO] or stenosis) was a historical and prospective multicenter registry at 38 centers in Japan. Patients with NVAF and acute LVO or stenosis who received apixaban within 14 days after onset were included. We conducted the post hoc analysis using the ALVO dataset. We compared patients with stenosis versus those without stenosis in terms of the primary outcome, which was defined as a composite of all-cause death, major bleeding events, and ischemic events 365 days after onset. RESULTS: Of the 662 patients, 54 (8.2%) patients were classified into the Stenosis group, and 104 patients of the total (16%) reached the primary outcome. The cumulative incidence of primary outcome was not significantly different between the No stenosis and the Stenosis groups (hazard ratio [HR] 1.2, 95% confidence interval [CI]: 0.64-2.4; p = 0.52). Even after adjustment for predictive clinical variates, no significant difference in the primary endpoint between the No stenosis and the Stenosis groups was shown (adjusted HR 1.2, 95% CI: 0.59-2.5; p = 0.60). Fifty patients (7.6%) used an antiplatelet with apixaban. Among the Stenosis group patients, the cumulative incidence of the primary outcome was significantly higher among patients treated with an antiplatelet and apixaban (HR 3.5, 95% CI: 1.0-12; p = 0.048). CONCLUSION: Apixaban monotherapy appears safe for the prevention of further adverse events in the Stenosis group patients similar to the No stenosis group patients. Concomitant use of an antiplatelet might not be favorable in patients with stenosis.

Reperfusion Therapy Brings Apixaban Administration Forward in Patients with Nonvalvular Arterial Fibrillation with Anterior Circulation Large Vessel Occlusion or Stenosis.

OBJECTIVE: The initiation of anticoagulant administration after large vessel occlusion (LVO) or stenosis with nonvalvular arterial fibrillation (NAVF) is controversial. We evaluate the timing of anticoagulation and its relationship with clinical factors. METHODS: We enrolled 595 anterior circulation LVO or stenosis with NAVF cases from 38 stroke centers. Laboratory data; activities of daily living; the Alberta Stroke Program Early CT Score (ASPECTS); the National Institutes of Health Stroke Scale (NIHSS) score; occluded artery; treatment methods; date of the initiation of apixaban administration and outcome were recorded. Multivariate analyses were performed after univariate analysis. RESULTS: The median start of apixaban administration after the stroke was 2 days (interquartile range, 1-5; range, 0-14). Multivariate analysis of variance showed that non-internal carotid artery occlusion (F value 4.60), reperfusion therapy (31.1), high ASPECTS (6.27) before anticoagulant intake, and absence of intracranial hemorrhage (12.9) were significantly correlated with early apixaban administration. Multiple logistic regression analysis for independent living at 90 days after the stroke showed significant factors: aging (odds, 0.94; 95% confidence interval [CI], 0.91-0.97); male (odds, 0.46; 95% CI, 0.26-0.79); prestroke independence (odds, 20.7; 95% CI, 6.48-93.9); number of white blood cells (odds, 0.99; 95% CI, 0.97-1.00); non-internal carotid artery occlusion; NIHSS score at 72 hours after the stroke (odds 0.92; 95% CI, 0.89-0.96); ASPECTS before apixaban intake (odds, 1.15; 95% CI, 1.00-1.31) and initiation of apixaban (odds, 0.91; 95% CI, 0.83-0.99). CONCLUSIONS: Early administration of apixaban is induced by nonsevere infarction, reperfusion therapy or none of intracranial hemorrhage and it correlates with an independent long-term outcome.

Endovascular Therapy for an Aneurysm of a Distal Posterior Inferior Cerebellar Artery via the Ipsilateral Persistent Primitive Proatlantal Artery: A Case Report.

Objective: We describe the rare case of a patient who was treated for a ruptured distal posterior inferior cerebellar artery (PICA) aneurysm via an ipsilateral persistent primitive proatlantal artery (PPPA). Case Presentation: An 86-year-old female with a medical history of hypertension presented with headache and nausea. CT showed subarachnoid hemorrhage in the posterior cranial fossa, and CTA revealed an aneurysm at the left-side distal PICA. In the left-sided common carotid angiography, the artery with a branch of the occipital artery from the external carotid artery was described. This artery continued as the V3 segment and entered the dura via the foramen magnum. The artery perfused the territory of the left vertebral artery and PICA. We concluded that the artery, which entered the dura, was a PPPA. We decided to perform endovascular therapy that passed through the PPPA. The aneurysm was located in the cortical segments, beyond the cranial loop. We decided that parent artery occlusion (PAO) would be more effective than selective coil embolization to achieve safe and adequate hemostasis. The patient had a good outcome with PAO not assessing collateral circulation. Conclusion: The emergency endovascular treatment with rare vascular variations requires accurate anatomical knowledge for treatment.

Early rebleeding of a foramen magnum dural arteriovenous fistula: A case report and review of the literature.

Foramen magnum dural arteriovenous fistula (FM-DAVF) is a subset of craniocervical junction arteriovenous fistulas. We report a rare case of FM-DAVF with early rebleeding and review the literature. A 50-year-old man experienced 3 episodes of intracranial bleeding from a vessel malformation in the acute stage. We identified an FM-DAVF, supplied by multiple feeding arteries (eg, left ascending pharyngeal artery) that drained into the straight sinus and left superior petrosal sinus. The draining vein had venous varices. We performed transarterial feeder embolization and surgical disconnection of the DAVF. Early rebleeding of FM-DAVF is rare. High-risk patients require risk assessment and appropriate treatment as soon as possible in the acute stage.

Effect of prior antiplatelet therapy on large vessel occlusion in patients with non-valvular atrial fibrillation newly initiated on apixaban.

INTRODUCTION: We evaluated the effect of prior antiplatelet therapy on large vessel occlusion (LVO) in patients with non-valvular atrial fibrillation (NVAF) newly initiated on apixaban. METHODS: Patients with acute LVO with acute stroke due to NVAF or stenosis with NVAF started on apixaban within 14 days of onset were enrolled. We compared incidence of major bleeding, cerebral hemorrhage, ischemic events, cerebral infarction, and all-cause mortality between patients with and without prior antiplatelet therapy for acute LVO. We also compared these events between patients who continued antiplatelet therapy after onset (continued group) and those who discontinued it (discontinued group). Hazard ratios were estimated after adjusting for confounders; interaction was evaluated considering intravenous thrombolysis (IVT) or endovascular treatment (EVT) according to major bleeding. RESULTS: The study comprised 686 eligible patients (excluded [n = 194]; enrolled [n = 492]). The antiplatelet group consisted of older patients (mean: 79 vs. 76 years; p = 0.006) and had a higher cumulative incidence of major bleeding (7.3% vs. 2.9%, p = 0.003). The incidence of ischemic events and all-cause mortality was similar between the groups. Among the 109 patients in the antiplatelet group, the cumulative incidence of major bleeding, ischemic events, and all-cause mortality was comparable between continued group (n = 26) and discontinued group (n = 83). There were no significant differences between groups with and without IVT/EVT. However, major bleeding occured more frequently in the antiplatelet group without IVT. CONCLUSION: Prior antiplatelet therapy for LVO in patients with NVAF newly initiated on apixaban was associated with major bleeding, which was more frequent in the antiplatelet group without IVT.

Usefulness of three-dimensional fast imaging employing steady-state acquisition MRI of large vessel occlusion for detecting occluded middle cerebral artery and internal carotid artery before acute mechanical thrombectomy.

OBJECTIVE: Acute mechanical thrombectomy (AMT) in patients with acute ischemic stroke from large vessel occlusion (LVO) is performed without directly identifying the occluded vessels. In this study, we evaluated whether 1.5 T magnetic resonance imaging (MRI) with 3D-fast imaging employing steady-state acquisition (FIESTA) could visualize the occluded intracranial middle cerebral artery (MCA) and internal carotid artery (ICA) before AMT. METHODS: This retrospective study included 21 consecutive patients who underwent time-of-flight magnetic resonance angiography (TOF MRA) and 3D-FIESTA MRI immediately before AMT. The patients also underwent TOF MRA after AMT and achieved TICI 2b or 3 by AMT at our hospital between February 2018 and April 2019. When LVO in the anterior circulation was detected by TOF MRA, 3D-FIESTA MRI was additionally performed. Then, the occluded intracranial MCA and ICA, including their branches, were constructed on the workstation with volume rendering. The obtained images were fused with the TOF MRA images to create combined 3D images. RESULTS: The length and top-to-bottom distance of the affected M1 segment (calculated by the ipsilateral-to-contralateral ratio) were 1.29 and 1.17, respectively, on 3D-FIESTA MRI before AMT and 1.34 and 1.24, respectively, on TOF MRA after AMT. We assessed the number of M2 segments branching from the affected M1/M2 junction and visualized the affected anterior temporal artery. The 3D-FIESTA MRI before AMT and TOF MRA after AMT were consistent in all patients, except for two who moved vigorously during imaging. CONCLUSIONS: Images acquired by 1.5T 3D-FIESTA MRI can visualize to predict the existing path of the occluded MCA and ICA before AMT in patients with LVO of the anterior circulation.

Clinical Result of Mechanical Thrombectomy Using Sofia Plus with Acute Ischemic Stroke Compared with the Stent Retriever.

OBJECTIVE: The Sofia catheter is a new large-bore aspiration catheter that allows easy access and good reperfusion. In this study, we analyzed the efficacy and safety of the Sofia catheter in comparison with stent retrievers as a contact aspiration thrombectomy (CAT) tool for large vessel occlusion. METHODS: We enrolled patients with acute ischemic stroke who underwent endovascular thrombectomy from April 2017 and April 2020 in our hospital. Patients were retrospectively reviewed and divided into the stent retriever group (SR), the Sofia group, and all cases group. RESULTS: A total of 114 patients were treated during the study period, including 27 in the stent retriever group and 15 in the Sofia group. Higher rates of the first-pass effect (FPE) (37% vs. 47%, P = 0.12) and significantly higher modified FPE (44% vs. 67%, P = 0.001) were observed in patients with SR and Sofia, respectively. Functional independence (modified Rankin Scale ≤2) at 30 days after onset was observed in 30% versus 47% (P = 0.47) of SR and Sofia, respectively. CONCLUSIONS: The Sofia Plus is a large-bore aspiration catheter with high FPE and good accessibility. Use of this catheter resulted better angiographic outcome compared with the stent retriever, but there was no difference in clinical outcomes in this study. Further studies are needed to compare in new generation aspiration catheters.

Safety of Early Administration of Apixaban on Clinical Outcomes in Patients with Acute Large Vessel Occlusion.

Early administration of direct oral anticoagulants in patients with acute large vessel occlusion (LVO) and nonvalvular atrial fibrillation (NVAF) is a concern, as endovascular therapy (EVT) became highly utilized. We conducted a historical and prospective multicenter registry at 38 centers in Japan from July 2016 to February 2018. Patients aged ≥ 20 years with NVAF and acute LVO or stenosis who received apixaban within 14 days from onset were included. We compared patients who received apixaban < 48 h (Early group) and ≥ 48 h (Late group) after onset in terms of the primary outcome (a composite of ischemic events, major bleeding events, and all-cause deaths). The secondary outcomes were each component of the primary outcome. Among the 686 patients, the median time from onset to administration was 2.5 days (range, 0-14; Early 263, Late 423). The Alberta Stroke Program Early CT Score (ASPECTS) and diffusion-weighted imaging (DWI)-ASPECTS) were significantly higher in the Early group than in the Late group. Recombinant tissue plasminogen activator (rt-PA) and EVT were more utilized in the Early group (rt-PA 46% vs. 35%, p = 0.003; EVT 62% vs. 46%, p < 0.0001). The cumulative incidence of primary outcome was similar between groups (ischemic events: Early 1.9% vs. Late 0.5% at 30 days; 3.5% vs. 0.7% at 90 days, major bleeding 3.4% vs. 2.9% at 30 days; 5.0% vs. 3.4% at 90 days). Early administration of apixaban (< 48 h), after onset of acute LVO in patients with NVAF, was generally safe compared with those who received it Late (≥ 48 h). http://www.clinicaltrials.gov . Unique identifier: NCT02818868 (June 30, 2016).

Mechanical Thrombectomy for Large Vessel Occlusion via the Transbrachial Approach: Case Series.

Mechanical thrombectomy has become a standard treatment for acute ischemic stroke with large vessel occlusion. In aged patients, it is difficult to guide the catheter via the transfemoral approach due to vessel tortuosity and aortic elongation. We report our preliminary clinical experience using the transbrachial approach. Among the 119 patients who underwent thrombectomy from April 2018 to December 2019, a total of 5 patients were treated via the transbrachial approach. Clinical outcomes were retrospectively analyzed. Successful reperfusion was achieved in 4 out of 5 cases. There was 1 death due to symptomatic intracranial hemorrhage. One patient had a good outcome at discharge. There were no access-site complications associated with any of these cases. Transbrachial access for mechanical thrombectomy is feasible and can provide an alternative to the transfemoral approach.

Parent Artery Occlusion for Treatment of a Traumatic Pericallosal Artery Aneurysm: Case Report and Review of the Literature.

BACKGROUND: Traumatic intracranial aneurysms are rare complications after head trauma. This report describes the case of a patient with a traumatic pericallosal aneurysm. CASE DESCRIPTION: A 73-year-old man developed headache and lower limb paresis, and emergency computed tomography scan revealed a hematoma in the corpus callosum. We performed coil embolization for a pericallosal aneurysm, but follow-up angiography showed recurrence of the aneurysm 6 days after the surgery. We diagnosed this as a traumatic aneurysm and subsequently performed parent artery occlusion without any complications. CONCLUSIONS: We performed parent artery occlusion for a traumatic aneurysm of the pericallosal artery without complications. Pericallosal aneurysms are rare, but we must consider them when encountering a delayed hematoma around the corpus callosum.

Clinical Results of Mechanical Thrombectomy in Nonagenarians with Acute Ischemic Stroke.

Objective: Multiple randomized trials have demonstrated the efficacy of mechanical thrombectomy (MT), but very elderly patients aged ≥90 years were excluded. It remains uncertain whether endovascular therapy is effective for nonagenarians. The objective of this study was to investigate the effectiveness and safety of MT in nonagenarians. Methods: Between January 2016 and March 2019, acute ischemic stroke patients aged ≥80 years who underwent MT at our hospital were retrospectively reviewed. Patients with a baseline pre-stroke modified Rankin Scale (mRS) score ≥3 were excluded from the analysis. They were divided into octogenarians (80-89 years old) and nonagenarians (90-99 years old). Results: Forty-five patients met the inclusion criteria, including 34 octogenarians and 11 nonagenarians. Nonagenarians were more likely to be female (47.0% vs 90.9%; p <0.05). There was a significantly lower rate of a pre-stroke mRS score of 0-1 among the nonagenarians (91.1% vs 63.6%; p <0.05). Revascularization was successful in 71.0% and 81.8% (p = 0.46) of octogenarians and nonagenarians, respectively. Functional independence (mRS ≤2) at discharge was observed in 26.4% vs 27.2% (p = 0.95) of octogenarians and nonagenarians, respectively. Conclusion: MT in nonagenarians can be considered safe without increasing hemorrhagic complications in comparison with that in octogenarians. One in four patients may have a good outcome and obtain effects equivalent to those in octogenarians if they have a good pre-stroke functional status.

Clinical Outcomes of Mechanical Thrombectomy for Acute Ischemic Stroke in Transfer Cases.

Objective: There are regional disparities in endovascular thrombectomy, and problems with emergency transport systems and hospital collaboration when transferring need to be addressed. In this study, the clinical outcomes of endovascular thrombectomy for transferred patients were analyzed. Methods: Acute ischemic stroke patients who underwent endovascular thrombectomy between January 2016 and March 2019 were enrolled. They were retrospectively reviewed and divided into the direct group and transfer group, and we compared treatment results and clinical outcomes between them. Results: In all, 122 patients met the inclusion criteria, comprising 93 patients in the direct group and 29 patients in the transfer group. The time from onset to door of our hospital was longer in the transfer group than in the direct group (73 minutes vs. 158 minutes, P = 0.80), but the time from arrival to reperfusion was significantly shorter in the transfer group (139 minutes vs. 106 minutes, P = 0.001). As the time from onset to reperfusion did not differ significantly between the two groups (220 minutes vs. 256 minutes, P = 0.60), there was no significant difference in good outcome at discharge (38.7 vs. 41.3%, P = 0.79). Conclusion: Clinical outcomes of transferred patients for endovascular thrombectomy may be equivalent to those of directly transported patients. Promoting close hospital cooperation may improve clinical outcomes and resolve regional disparities.

[Comparison of Time-intensity Curve with Gadobenatedimeglumine and Gadobutrol on Multiphase Contrast-enhanced Breast MRI].

The purpose of this study was to compare the time-intensity curve (TIC) on multiphase contrast-enhanced breast magnetic resonance imaging (MRI) between Gadobenatedimeglumine (Gd-DTPA) and Gadobutrol. We assessed the images of 53 cases obtained from MRI that had malignant findings by pathology from October 2015 to October 2016 in our institute. Gd-DTPA and Gadobutrol were administrated in 16 and 37 cases, respectively. The TIC of the lesion was classified according to the Kuhl's method (type I: persistent pattern, type II: plateau pattern and type III: washout pattern). Type III was the most common TIC pattern in both the groups (Gd-DTPA, 12 cases; Gadobutrol, 18 cases). Type II was the second common TIC pattern in Gadobutrol group (12 cases). As a result, there was no significant difference in TIC analysis between Gd-DTPA and gadobutrol. In conclusion, the contrast between Gd-DTPA and Gadobutrol contrast media did not differ in TIC pattern of multiphasic contrast-enhanced breast MRI.

[A Case of Moyamoya Disease with Postoperative Cerebral Hyperperfusion Syndrome Followed by Cerebral Infarction due to Watershed Shift].

The concept of "watershed shift"(WS)has been proposed as a cause of the ischemic complications following a superficial temporal artery-middle cerebral artery(STA-MCA)bypass operation performed for the management of moyamoya disease. Previous reports have observed that only 1.2-5.7% of the patients who underwent a bypass operation for the management of moyamoya disease developed cerebral infarction secondary to the WS phenomenon. To date, the WS phenomenon has not been objectively proven on imaging studies. We describe a 39-year-old woman who presented with right facial palsy and aphasia. Magnetic resonance imaging revealed cerebral infarction in the left frontal lobe secondary to moyamoya disease. Three days after undergoing the left STA-MCA bypass procedure, she showed deterioration in aphasia secondary to the occurrence of cerebral hyperperfusion syndrome(CHPS). Diffusion-weighted imaging(DWI)performed on postoperative day(POD)1 and 5 showed no area of high signal intensity. DWI performed on POD 8 showed an area of high signal intensity in the deep white matter of the left parietal lobe outside the range of the craniotomy. Postoperative fusion images of computed tomography angiography and DWI performed on POD 8 showed that the blood flow through the MCA from the bypass graft and that through the posterior cerebral artery crossed each other at the surface of the subcortical infarction. In the present case, the WS could be directly confirmed on imaging studies, and the cerebral infarction may have occurred secondary to WS concomitant with CHPS. Clinicians need to be aware of the WS phenomenon even after performing a direct bypass to treat adults with moyamoya disease.

A simulation study for estimating scatter fraction in whole-body 18F-FDG PET/CT.

Whereas Monte Carlo (MC) simulation is widely utilized in estimation of the scatter component, a simulation model which can calculate the scatter fraction (SF) of each patient is needed for making an accurate image quality assessment for clinical PET images based on the noise equivalent count. In this study, an MC simulation model was constructed which can calculate the SF for various phantoms. We utilized the Geant4 toolkit based on MC simulation to make a model of a PET scanner with a scatter phantom, and SFs calculated with this model were compared with the SF (SFconstant: 44%) measured with use of an actual PET scanner. Additionally, the SF values for an anthropomorphic phantom were calculated from its voxel phantom. Furthermore, we evaluated the impact on the SF due to the difference in the source distribution inside the phantom. The SF calculated from the scatter phantom in the MC simulation was 44%, the same as the SFconstant value. The average SF for the anthropomorphic phantom was 41%, but there was a maximum of 14 percentage points difference between each scan range, and the maximum difference in the SF was 8 percentage points for the difference in the source distribution. We constructed an MC simulation model which can calculate SFs for various phantoms. The SF was confirmed to be affected significantly by the source distribution. We judged that the actually measured SFconstant obtained from the PET scanner with the scatter phantom was not suitable for the assessment of the quality of all patient images.

[Variation in the quality of CT images of the upper abdomen when CT automatic exposure control is employed].

The aim of this study was to analyze the reason for variation of image quality in the upper abdomen CT with the use of CT-AEC. The CT investigated was 3D modulation in the 16MDCT and LSCT phantom was used to simulate the patient. When there was a phase difference, an image noise increase of around 15% at the maximum was accepted. It is concluded that the major reason for variation in image quality is respiratory motion and the importance of respiration control must be recognized.