Patient weight-based acquisition protocols to optimize18F-FDG PET/CT image quality

The choice of injected dose of 18F-FDG and acquisition time is important in obtaining consistently high-quality PET images. The aim of this study was to determine the optimal acquisition protocols based on patient weight for 3-dimensional lutetium oxyorthosilicate PET/CT. Methods: This study was a retrospective analysis of 76 patients ranging from 29 to 101 kg who were injected with 228-395.2 MBq of 18F-FDG for PET imaging. The study population was divided into 4 weightbased groups: less than 45 kg (group 1), 45-59 kg (group 2), 60-74 kg (group 3), and 75 kg or more (group 4). We measured the true coincidence rate, random coincidence rate, noise-equivalent counting rate (NECR), and random fraction and evaluated image quality by the coefficient of variance (COV) in the largest liver slices. Results: The true coincidence rate, random coincidence rate, and NECR significantly increased with increasing injected dose per kilogram (r 5 0.91, 0.83, and 0.90; all P < 0.01). NECR maximized at 10.11 MB/kg in underweight patients. The true coincidence rate differed significantly among the 4 groups, except for group 3 versus group 4 (P < 0.01). The ratio of the true coincidence rate for group 2 to groups 3 and 4 was 1.4 and 1.6, respectively. The average random fraction for all 4 groups was approximately 35%. The COV of the 4 groups differed for all pairs (P < 0.01). The COVs in overweight patients were larger than those in underweight patients, and image quality in overweight patients was poor. Conclusion: We modified acquisition protocols for 18F-FDG PET/CT according to the characteristics of a 3-dimensional lutetium orthosilicate PET scanner and PET image quality based on patient weight. The optimal acquisition time was approximately 1.4-1.6 times longer in overweight patients than in normal-weight patients. Estimation of optimal acquisition times using the true coincidence rate is more important than other variables in improving PET image quality. © 2011 by the Society of Nuclear Medicine, Inc.Thesis of Nagaki, Akio / 長木 昭男 博士学位論文(金沢大学 / 大学院医薬保健学総合研究科

CT tube current for attenuation map in a combined PET/CT system: obese patient simulated phantom study

Objective: The CT portion of PET/CT provides attenuation correction of the PET emission scan. This study was performed to evaluate how much the CT tube current can be lowered while still providing attenuation maps on PET images. Methods: Two body phantoms (outside diameters of 300 and 500 mm) were used to investigate, and PET/CT acquisitions were performed with an Aquiduo PCA-7000B (Toshiba Medical Systems, Otawara, Japan). The CT scan was performed with the following parameters (120 kVp; 0.5-s rotation; 10, 20, 40, 80, 160, 200, 320, 460 mA). After the CT scan, PET images for 18F-FDG (5.3 kBq/mL) were obtained for 4 min/bed position. The linear attenuation coefficients for 18F-FDG in 300- and 500-mm phantoms, pixel values and SD of CT images, radioactivity concentration values and hot- and cold-sphere contrast on PET images in the 500-mm phantom were evaluated. Results: In the 300-mm phantom, all eight tube currents gave average linear attenuation coefficients of approximately 0.095 cm -1. In contrast, the average linear attenuation coefficients of the 500-mm phantom at 10, 20, and 40 mA were significantly decreased (0.081, 0.087, and 0.092 cm -1, respectively; p < 0.05) as compared to 0.096 cm -1 of the other tube currents. Further, CT pixel values decreased 10 and 20 mA. Thus, the background radioactivity concentration values at 10 and 20 mA were substantially underestimated to be 57 and 80%, respectively (p < 0.05); the hot-sphere contrast values at 10 and 20 mA were 0.26 and 0.29; the cold-sphere contrast values at 10, 20, and 40 mA were -0.33, -0.16, and 0.08. Conclusions: Although the linear attenuation coefficients in the 300-mm phantom remained the same with varying CT tube currents, the 500-mm phantom yielded significant differences in the range 10-40 mA. Therefore, the CT tube currents for attenuation correction should be adjusted over 40 mA in obese patients. © 2012 The Japanese Society of Nuclear Medicine

タリウム発生光子の異なった吸収差を利用したSPECTの減弱補正と散乱補正法の開発

心筋では,減弱によるカウントの低下と散乱線による分解能の劣化により,病変を過小評価することが指摘されている。近年,外部線源を用いるTransmission CT(TCT)やX線CTによる減弱補正の開発が行われているが,外部線源の利用は煩雑であるため,十分な臨床応用はされていない。本研究では,外部線源を用いないでTl-201発生光子の異なった2種類のエネルギー差,ここでは主要エネルギーである71keV(放出割合75%)のHg-201特性X線と167keV(放出割合10%)のガンマ線の減弱差を利用し,さらに71keVへの散乱線補正を組み合わせることで,そのエネルギー差(減弱の差)を拡大させる減弱・散乱線補正法を開発した。平成18年度は,この理論を正常および虚血性心疾患をシミュレーションした心筋ファントムを用い,その理論の妥当性を検証した。さらに,^TlCl心筋血流SPECT検査に臨床応用し,従来の減弱・散乱線補正を行わないSPECT画像をリファレンスとして散乱線補正のみ行った場合と吸収・減弱補正を行った場合のSPECT画像を作成後,画質,視覚評価および定量的評価を比較,検討した。心筋ファントムにおいて,正常心筋モデルでは肝臓放射能の有無にかかわらず下壁のカウントが減弱・散乱線補正により上昇し,心筋全体がより均一な分布になった。心筋梗塞モデルも同様に,梗塞部以外の正常領域は均一になり,かつ梗塞部は低いカウントが保たれていた。臨床例においては,正常例では心筋全体がより均一な分布となった。前壁および下壁に病変を有する疾患で,画質および病変検出能を検討した結果,本法の使用により画質は改善された。病変検出能は補正によって検出能が下がることはなく,診断能においても問題がないと考えられた。減弱・散乱線補正をすることにより,心筋全体のカウントが均一になり心筋壁・心室腔が明瞭に描出され,特に下壁での減弱・散乱線補正の効果が著明であった。このことから,外部線源を用いない本法は臨床においても有用であると考えられた。We devised a new correction method that combined attenuation correction using a difference of intrinsic dual-energy between lower energy emissions (71keV) and higher energy emissions (167keV) without transmission scan and Compton scatter correction using triple-energy window (TEW) method for 71keV because of enhancing a difference of intrinsic dual-energy in ^TlCl (^Tl), and applied to cardiac phantom and myocardial perfusion SPECT studies.Attenuation coefficients ratio and counts ratio for 71keV/167keV were calculated from SPECT data acquired by energy window of 71keV and 167keV, respectively. Defects with the same thickness were inserted on the inner surface of a myocardial phantom at 2 difference locations: anterior (ANT) and inferior (INF). The myocardial perfusion SPECT studies was performed with ^Tl using the same protocol that we use for patients. The images reconstructed by non-attenuation-scatter (A(-)S(-)), only scatter (A(-)S(+)) and attenuation-scatter (A(+)S (+)) correction were compared by visual and quantitative analysis, respectively.The adequate attenuation coefficients ratio and counts ratio for 71keV/167keV were 2.277 and 5, respectively. In the normal myocardial phantom, the INF wall was improved by attenuation-scatter (A(+)S(+)) correction, and the whole of the myocardial wall was uniform.In the ANT and INF defect wall phantom, the tracer distribution except defect wall were uniform, and the all defects were clearly detected. In patients with known or suspected CAD, defect regions were clearly discriminated by technique, the detectability for CAD was improved.It is suggested that a new correction method that combined attenuation correction using a difference of intrinsic dual-energy and Compton scatter correction using triple-energy window (TEW) method for 71keV is useful in ^Tl myocardial perfusion SPECT studies. This may reduce both of attenuation and scatter artifacts, and allow the more accurate assessment of patients with known or suspected CAD.研究課題/領域番号:17591255, 研究期間(年度):2005-2006出典：「タリウム発生光子の異なった吸収差を利用したSPECTの減弱補正と散乱補正法の開発」研究成果報告書　課題番号17591255 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

核医学的手法による動物モデルを用いた臓器血流の定量化の研究: γ線の吸収散乱因子

心筋血流製剤における肝臓,肺臓および腸管の集積が画像から算出した心筋摂取率に及ぼす影響を検討するために,^Tc-tetrofosminを投与したラットをガンマカメラでプラナー像(以下,PI)で撮像し,画像から得られた各臓器の摂取率と,摘出臓器(心臓,肺臓,肝臓,血液および腸管)をウェル型シンチレーションカウンタ(以下,WC)で測定した摂取率の値を経時的に比較した。WCによる心臓摂取率は,投与30分後(1.671%±0.306%)まで増加し,その後緩やかに減少した。一方,PIによる摂取率は,投与15分後(1.814%±0.518%)に最大値となり,両者の差は投与10分後(PI/WC比:約1.6)に最大となった。WCによる肺摂取率は投与15分後(0.870%±0.312%)から次第に減少したが,PIによる摂取率は10分後(1.139%±0.376%)で高値を示し,その後ほとんど変化を認めなかった。またWCによる肝臓摂取率は投与5分後(0.768%±0.193%)から30分後(0.692%±0.273%)までほとんど変化を認めず,その後次第に減少したが,PIによる摂取率はWCに比し,10分後(1.949%±0.596%,PI/WC比:約3.3倍),15分後(1.845%±0.642%,PI/WC比:約2.3倍)で高値を示した。WCによる心臓/臓器比はいずれも経時的に増加したが,PIでは経時的変化が少なく,低値であった。PIによる十二指腸と上部小腸の摂取率は投与後10分(1.228%±0.602%,2.245%±1.936%)で最大となり,各腸管壁とその内容物の摂取率の割合は,十二指腸,小腸ともに90%以上が肝臓から排泄された内容物によるものであった。以上より,心臓,肺臓,肝臓の摂取率は,いずれもWCによる値に比べPIでは有意に高値を示した。特に投与後早期で両者の差は大となり,投与10分後では,PIによる心臓の摂取率とWCによる摂取率との間に大きな乖離がみられた。PIから算出された摂取率は必ずしも真の値を正確に表しておらず,心臓に隣接する肝臓,腸管などの高集積による散乱線の関与が大きいと思われた。It\u27s reported that the duodenum and the small intestine of the activity excreted from the liver and gallbladder can lead to interference with the myocardial uptake. To study how precisely images reflect tracer uptake in a myocardium, as fundamental experiment to examine the influence that accumulation of the liver and alimentary tract (except esophagus) of the activity excreted from the liver gave to the myocardium image in the technetium-99m myocardium perfusion tracer, we administered ^Tc-tetrofosmin (following, Tetrofosmin) to a normal rat and compared with measured value obtained by a gamma camera and an actual survey value after the organs extraction. Methods : Thirty-three rats were measured for 5, 10, 15, 30, 45, 60, 90 and 120min after the administration of Tetrofosmin. The accumulated rates for the myocardium, the lung, the liver, the duodenum, the small intestine, the rectum and the blood with a well-type scintillation counter (WC) were assessed as a percentage of t he injected dose per gram of tissue (%ID/g). The accumulated rates for each organ with the planar imaging (PI) were assessed as a percentage of the injected dose per pixel (%ID/pixel) establishing regions of interest (ROIs) in each organ. The accumulated rates for each organ, the PI-to-WC ratio and the heart-to-organ ratios calculated by PI and WC were compared. Results : The accumulated rate for the heart with WC increased until 30 min (1.671%±0.306%) after the injection, and subsequently decreased. On the other hand, peak of the accumulated rate with PI was shown at 15 min (1.814%±0.518%) after the injection. Particularly a difference of both was higher in 10 min (PI/WC ratio : about 1.6 times) of the early phase. The accumulated rate for the lung with WC was maximum at 15 min (0.870%±0.312%) after the injection. The accumulated rate with PI, however, showed the maximum value at 10 min (1.139%±0.376%), and a variation of the accumulated rate was hardly recognized 10 min later. The accumulated rate for the liver with WC was hardly shown a marked variance from 5min (0.768%±0.193%) to 30min (0.692%±0.273%), and a tendency of decrease was showed slowly. On the other hand, the accumulated rate with PI was more highly than that with WC in the whole, and high values were showed in 10 min (PI/WC ratio : about 3.3 times) and 15 min (PI/WC ratio : about 2.3 times) in particular. The accumulated rate for the duodenum and the upper small intestine was maximum in 10 min (1.228%±0.602%, 2.245%±1.936%) after the injection, and approximately 90% of ^Tc-tetrofosmin were the duodenum excrements. Conclusion : The accumulated rates for each organ with PI were showed higher than that with WC. The difference of both, particularly, was stronger in early phase after the injection. The accumulated rate for the heart with PI was shown significant higher than that with WC at 10 min. The interference of Compton scatter from the liver, duodenum and small intestine was suggested as one of these causes.研究課題/領域番号:10670836, 研究期間(年度):1998-1999出典：「核医学的手法による動物モデルを用いた臓器血流の定量化の研究: γ線の吸収散乱因子」研究成果報告書　課題番号10670836 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

How precisely do SPECT images reflect tracer uptake in myocardial infarction? A comparison of thallium-201 and technetium-99m using a myocardial phantom

金沢大学大学院医学系研究科量子医療技術学Objective: We compared the count ratios of 201Tl and 99mTc on SPECT images and the true radioactivity in a myocardial phantom to study how precisely SPECT images reflect tracer uptake in myocardial infarction. Methods: A defect with 20%, 40% or 60% of normal myocardial radioactivity was placed in the anterior or inferior wall of a myocardial phantom to simulate myocardial infarction. Lung radioactivity was kept at 10% or 30% of normal myocardial radioactivity. The count ratio on short-axis SPECT images was calculated using the circumferential profile curve analysis. Results: The count ratios of 201Tl and 99mTc SPECT images with an anterior wall defect was lower than the true radioactivity in the phantom. The count ratio on SPECT images with the inferior wall defect was greater than the true radioactivity for the 20% and 40% defects and lower for the 60% defect. Conclusion: SPECT images overestimated decreased perfusion in the anterior wall. SPECT images underestimated decreased perfusion for 20% and 40% perfusion defects in the inferior wall

Automated segmentation of the skeleton in whole-body bone scans: Influence of difference in atlas

AIM: Automated segmentation of the skeleton is the first step for quantitative analysis and computer-aided diagnosis (CAD) of whole-body bone scans. The purpose of this study was to examine the influence of differences in skeletal atlas on the automated segmentation of skeletons in a Japanese patient group. METHODS: The study was based on a bone scan CAD system that included a skeletal atlas obtained using 10 normal bone scans from European patients and 23 normal bone scans from Japanese patients. These were incorporated into the CAD system. The performance of the skeletal segmentation, based on either the European or the Japanese Atlas, was evaluated independently by three observers in a group of 50 randomly selected bone scans from Japanese patients. RESULTS: The skeletal segmentation was classified as correct in 41-44 of the 50 cases by the three observers using the Japanese atlas. The corresponding results were 15-18 of the 50 cases using the European atlas, and this difference was statistically significant (P<0.001). The anatomical areas most commonly classified as not correct were the skull, cervical vertebrae, and ribs. CONCLUSION: Automated segmentation of the skeleton in a Japanese patient group was more successful when the CAD system based on a Japanese atlas was used than when the corresponding system based on a European atlas was used. The results of this study indicate that it is of value to use a skeletal atlas based on normal Japanese bone scans in a CAD system for Japanese patients. © 2012 Wolters Kluwer Health | Lippincott Williams &Wilkins

Elimination of scattered gamma rays from injection sites using upper offset energy windows in sentinel lymph node scintigraphy

Objective: The identification of sentinel lymph nodes (SLNs) near injection sites is difficult because of scattered gamma rays. The purpose of this study was to investigate the optimal energy windows for elimination of scattered gamma rays in order to improve the detection of SLNs. Methods: The clinical study group consisted of 56 female patients with breast cancer. While the energy was centred at 140 keV with a 20% window for Tc-99m, this energy window was divided into five subwindows with every 4% in planar imaging. Regions of interest were placed on SLNs and the background, and contrast was calculated using a standard equation. The confidence levels of interpretations were evaluated using a five-grade scale. Results: The contrast provided by 145.6 keV ± 2% was the best, followed by 140 keV ± 2%, 151.2 keV ± 2%, 134.4 keV ± 2% and 128.8 keV ± 2% in that order. When 128.8 keV ± 2% and 134.4 keV ± 2% were eliminated from 140 keV ± 10% (145.6 keV ± 6%), the contrast of SLNs improved significantly. The confidence levels of interpretation and detection rate provided by the planar images with 140 keV ± 10% were 4.74 ± 0.58 and 94.8%, respectively, and those provided by 145.6 keV ± 6% were 4.94 ± 0.20 and 100%. Conclusion: Because lower energy windows contain many scattered gamma rays, upper offset energy windows, which exclude lower energy windows, improve the image contrast of SLNs near injection sites. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved

Nuclear myocardial perfusion imaging using thallium-201 with a novel multifocal collimator SPECT/CT: IQ-SPECT versus conventional protocols in normal subjects

Objective A novel multifocal collimator, IQ-SPECT (Siemens) consists of SMARTZOOM, cardio-centric and 3D iterative SPECT reconstruction and makes it possible to perform MPI scans in a short time. The aims are to delineate the normal uptake in thallium-201 (201Tl) SPECT in each acquisition method and to compare the distribution between new and conventional protocol, especially in patients with normal imaging. Methods Forty patients (eight women, mean age of 75 years) who underwent myocardial perfusion imaging were included in the study. All patients underwent one-day protocol perfusion scan after an adenosine-stress test and at rest after administering201Tl and showed normal results. Acquisition was performed on a Symbia T6 equipped with a conventional dual-headed gamma camera system (Siemens ECAM) and with a multifocal SMARTZOOM collimator. Imaging was performed with a conventional system followed by IQ-SPECT/computed tomography (CT). Reconstruction was performed with or without X-ray CT-derived attenuation correction (AC). Two nuclear physicians blinded to clinical information interpreted all myocardial perfusion images. A semi-quantitative myocardial perfusion was analyzed by a 17-segment model with a 5-point visual scoring. The uptake of each segment was measured and left ventricular functions were analyzed by QPS software. Results IQ-SPECT provided good or excellent image quality. The quality of IQ-SPECT images without AC was similar to those of conventional LEHR study. Mid-inferior defect score (0.3 ± 0.5) in the conventional LEHR study was increased significantly in IQ-SPECT with AC (0 ± 0). IQ-SPECT with AC improved the mid-inferior decreased perfusion shown in conventional images. The apical tracer count in IQ-SPECT with AC was decreased compared to that in LEHR (0.1 ± 0.3 vs. 0.5 ± 0.7, p˂0.05). The left ventricular ejection fraction from IQ-SPECT was significantly higher than that from the LEHR collimator (p = 0.0009). Conclusion The images of IQ-SPECT acquired in a short time are equivalent to that of conventional LEHR. The results indicated that the IQ-SPECT system with AC is capable of correcting inferior artifacts with high image quality. © The Japanese Society of Nuclear Medicine 2015