Annals of Nuclear Medicine (v.29, #7)

This study investigated the prognostic value of preoperative breast-specific gamma imaging (BSGI) uptake measured by a semi-quantitative method in invasive ductal carcinoma (IDC).One hundred and sixty-two women with IDC who underwent preoperative BSGI were retrospectively enrolled. The tumor-to-normal tissue ratio (TNR) was measured on BSGI and correlated with histologic prognostic factors. The prognostic impact of TNR was tested with regard to progression-free survival (PFS) and compared with established prognostic factors.High TNR was significantly correlated with tumor size >2 cm (p < 0.001), high nuclear grade (p = 0.04), high histologic grade (p = 0.01), axillary node positivity (p = 0.04), ER negativity (p = 0.03), HER2 positivity (p = 0.01), and high MIB-1 index (p = 0.001). Among 162 patients, 14 experienced recurrence during mean follow-up time of 34.7 ± 14.9 months. In Kaplan–Meier survival analyses, high TNR (p < 0.001), high nuclear grade (p = 0.02), high histologic grade (p = 0.007), ER/PR negativity (p = 0.003 and p < 0.001, respectively), HER2 positivity (p = 0.01), triple negativity (p = 0.02), and high MIB-1 index (p = 0.02) showed a significant relationship with poor prognosis. Among them, high TNR was an independent poor prognostic factor in a multivariate regression analysis (p = 0.01).High BSGI uptake measured by a semi-quantitative method was correlated with diverse poor histologic prognostic factors and was an independent poor prognostic factor in invasive ductal cancer.
Keywords: Breast-specific gamma imaging; Tumor-to-normal tissue ratio; Invasive ductal carcinoma; Prognosis

Image accuracy and quality test in rate constant depending on reconstruction algorithms with and without incorporating PSF and TOF in PET imaging by Yukito Maeda; Nobuyuki Kudomi; Hiroyuki Yamamoto; Yuka Yamamoto; Yoshihiro Nishiyama (561-569).
Positron emission tomography allows imaging of patho-physiological information as a form of rate constants from scanned and reconstructed dynamic image. Some reconstruction algorithms incorporated with time of flight and point spread function have been developed, and quantitative accuracy and quality in the image have been investigated. However, feasibility of the rate constants from the dynamic image has not been directly investigated. We investigated the accuracy and quality in the rate constant by scanning a phantom filled simultaneously with 11C and 18F.We utilized a phantom filled with 18F–F solution in the main cylinder and with 11C-flumazenil solution in seven sub-cylinders. The phantom was scanned by a Biograph mCT and the scanned data were reconstructed with FBP- and OSEM-based algorithms incorporating with and without TOF and/or PSF corrections. Decay rate images as kinetic rate constant were computed for all the reconstructed images and quantitative accuracy and quality in the rate images were investigated.The obtained decay rates were not significantly different from the reference values for both isotopes for all applied algorithms when noise on image was not large. Respective SD was smaller in OSEM with TOF in the 11C-filled region.The present study suggests that OSEM incorporating with TOF provides reasonable quantitative accuracy and image quality regarding decay rates.
Keywords: Feasibility test; Rate constant; Phantom; PET; Kinetic analysis

Imaging characteristics and safety of florbetapir (18F) in Japanese healthy volunteers, patients with mild cognitive impairment and patients with Alzheimer’s disease by Chihiro Namiki; Yasushi Takita; Atsushi Iwata; Toshimitsu Momose; Michio Senda; Yoshiro Okubo; Abhinay D. Joshi; Ming Lu; Abigail Agbulos; Christopher Breault; Michael J. Pontecorvo (570-581).
The purpose of this study was to evaluate the performance characteristics and safety of florbetapir (I8F) positron emission tomography (PET) in patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI) and cognitively normal (CN) control patients from Japan.Florbetapir (I8F) PET was obtained in 48 subjects (15 AD patients, 15 MCI patients, and 18 CNs) within a multicenter phase 2/3 study. Amyloid burden was assessed visually and classified as positive or negative for pathologic levels of amyloid aggregation, blind to diagnostic classification. Cerebral to cerebellar standardized uptake value ratios (SUVRs) were determined from the florbetapir (I8F) PET images. Safety was assessed by monitoring adverse events, vital signs, clinical laboratory assessments, and electrocardiograms. Demographic variables and cognitive scales were summarized by using descriptive statistics for each group. Fisher’s exact test and one-way analysis of variance were used to compare amyloid positivity and mean SUVRs, respectively, between diagnostic groups.Florbetapir (I8F) PET was rated visually amyloid positive in 80.0 % of AD patients, 33.3 % of MCI patients, and 16.7 % of CNs. Mean SUVRs were highest in the AD group and lowest in the CN group for each brain region (P < 0.01) and globally (P < 0.05). Kappa statistics showed strong inter-reader agreement (Fleiss’ kappa = 0.82) and individual reader’s agreement with the majority of readers (kappa ranged from 0.79 to 1.0). Seventeen of the 48 subjects (35.4 %) were Apolipoprotein E genotype ε4 positive, which included 10 subjects in the AD group and 7 subjects in the MCI group. A total of 6 subjects (5 of whom were in the CN group) had at least 1 treatment-emergent adverse event (TEAE).These data indicate that amyloid positivity increased with diagnostic category (CN < MCI < AD) and are consistent with expected rates of amyloid positivity among individuals with clinical diagnoses of AD and MCI. In addition, these results were similar to those obtained in United States studies. Florbetapir (18F) was safe and well tolerated. The reliability of both qualitative and quantitative assessments of florbetapir (18F) in this study population provides support for potential use in clinical settings in Japan.
Keywords: Alzheimer’s disease; PET; Amyloid; Florbetapir; Amyvid; Japan

Relationship between biodistribution of a novel thymidine phosphorylase (TP) imaging probe and TP expression levels in normal mice by Songji Zhao; Hua Li; Ken-ichi Nishijima; Yan Zhao; Hiromichi Akizawa; Yoichi Shimizu; Kazue Ohkura; Nagara Tamaki; Yuji Kuge (582-587).
Thymidine phosphorylase (TP) is a key enzyme in the pyrimidine nucleoside salvage pathway and its expression is upregulated in a wide variety of solid tumors. In mice, we previously observed high and specific accumulation levels of our TP imaging probe, radioiodinated 5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil (IIMU) not only in high-TP-expressing tumors, but also in the liver and small intestine. To clarify the reason for the high accumulation levels of radioiodinated IIMU in the liver and small intestine, we investigated the expression levels of TP in mice in comparison with the biodistribution of radioiodinated IIMU (123I-IIMU).BALB/cCrSlc mice were injected with 123I-IIMU, and the radioactivity levels [%ID/g (normalized to a mouse of 25 g body weight)] in the tissues of interest were determined 0.5, 1, 3 and 24 h after the injection (n = 5, each time point). To determine the expression levels of TP, BALB/cCrSlc and ddy mice (n = 3/each strain) were euthanized, and the heart, liver, lung, spleen, kidney, stomach, small intestine, large intestine and brain were collected. The mRNA and protein expression levels of TP in these organs were examined by quantitative reverse transcription-polymerase chain reaction and western blot analyses, respectively.In BALB/cCrSlc mice administered 123I-IIMU, markedly high radioactivity levels were observed in the liver [1.568 ± 0.237 (%ID/g)] and small intestine [0.506 ± 0.082 (%ID/g)], whereas those in the other tissues were fairly low [<0.010 ± 0.003 (%ID/g)] 30 min after the injection. The highest expression levels of TP mRNA were also observed in the liver and small intestine among the tissues tested. Immunoblotting showed intense immunoreactive bands of the TP protein for the liver and small intestine, whereas no notable bands were detected for other tissues. Similar expression profiles of TP mRNA and protein were observed in ddy mice.We confirmed TP expression in various tissues of mice at the mRNA and protein levels: high TP expression levels were observed in the liver and small intestine. These high TP expression levels are consistent with the high accumulation levels of 123I-IIMU in these tissues. Our results may provide important information about the physiological accumulation of 123I-IIMU, which may be useful for the clinical diagnostic imaging of TP.
Keywords: Thymidine phosphorylase expression; 5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil (IIMU); Liver; Small intestine; Normal mouse tissues

Assessment of absolute Tc-99m tetrofosmin retention in the myocardium as an index of myocardial blood flow and coronary flow reserve by gated-SPECT/CT: a feasibility study by Dimitris J. Apostolopoulos; Agaristi Kaspiri; Trifon Spyridonidis; Nikolaos Patsouras; Christos A. Savvopoulos; Pericles Davlouros; Pavlos. J. Vassilakos; Dimitrios Alexopoulos (588-602).
Estimation of myocardial blood flow (MBF) and coronary flow reserve (CFR) by SPECT myocardial perfusion imaging (MPI) remains challenging. Our aim was to approximate MBF and CFR by quantifying the absolute Tc-99m tetrofosmin retention in the myocardium via gated-SPECT/CT MPI.Tracer retention was calculated on the basis of the microsphere kinetic model and served as an index of MBF at stress and rest (sMBFi, rMBFi). CFR was given by the sMBFi/rMBFi ratio. A planar first-pass acquisition during dipyridamole stress and at rest provided the data for tracer input determination. The input was represented by the integral of a gamma variate fitted on the time-activity curve of the left ventricle. Gated-SPECT/CT was performed 1 h post tracer injection and myocardial activity was measured in attenuation-corrected transaxial slices by a threshold VOI. The input was also compensated for tissue attenuation by measuring the distance from the centre of the left ventricle to the body surface on fused SPECT/CT slices. Input and uptake results were adjusted for planar-SPECT counting geometry differences by the aid of a phantom experiment. Thirty-nine subjects with low probability of coronary artery disease (CAD), age lower than 75 years and normal MPI (control group) were compared with 57 patients with documented CAD (CAD group).CFR and sMBFi values of CAD patients (1.39 ± 0.37 and 1.42 ± 0.35 ml/min/g) were considerably lower (p < 0.0001) than controls (1.68 ± 0.25 and 1.72 ± 0.37 ml/min/g). Significant difference in CFR (p = 0.03) was also noted between CAD patients with normal MPI (1.48 ± 0.38) and controls. However, sMBFi managed to discriminate certain CAD subgroups (normal MPI/ischemia/scar/scar and ischemia) more efficiently than CFR. Maximum heart rate-blood pressure product (RPP) during stress was an independent predictor of sMBFi and CFR. The other independent CFR correlates were resting RPP and diabetes mellitus, while sMBFi was associated with age, sex, smoking, and stress perfusion defects.Despite the low myocardial extraction fraction of Tc-99m tetrofosmin, an approximation of MBF and CFR is feasible with gated-SPECT/CT MPI. These flow indices together were able to discriminate CAD patients from controls and stratify different patient subgroups.
Keywords: Myocardial blood flow; Coronary flow reserve; SPECT/CT; Tetrofosmin

A diffuse hepatic uptake (DHU) on radioiodine whole-body scans (WBS) after 131I therapy is caused by 131I-labeled iodoproteins, particularly 131I-labeled thyroglobulin (Tg). We hypothesized that the DHU intensity after 131I therapy might correlate with subsequent serum Tg reduction, suggesting that DHU reflects destruction of functioning thyroid tissue as measured by serum Tg.We retrospectively reviewed the medical records and 131I WBSs of 47 patients treated with 131I therapy for distant metastasis from differentiated thyroid cancer (M:F = 15:32, median age 45 years, range 11–74 years). All patients received post-ablative 131I scans (PAWBS) at first 131I ablation after total thyroidectomy and post-therapy 131I scan (PTWBS) at second 131I therapy. The DHU intensities of the PAWBS and PTWBS were classified into 3 grades: 1, faint; 2, modest; and 3, intense. Serum thyroid-stimulating hormone-stimulated Tg (sTg) levels were measured at the time of each therapy and 1 year after the second 131I therapy.One year after the second 131I therapy, 10 patients (21.3 %) were in remission and 37 (78.7 %) had persistent disease. The DHU intensity on PAWBS correlated with the percentage sTg reduction at the next follow-up point (σ = 0.466, p = 0.0016). The patients with intense DHU on PTWBS tended to have a higher percentage sTg reduction than the other patients, although statistical significances were marginal (Spearman’s rank correlation: σ = 0.304, p = 0.054; Kruskal–Wallis test: p = 0.067). In univariate analysis, the DHU grades on PAWBS and the initial sTg levels were significantly different between patients in remission and those with persistent disease (PAWBS: p = 0.022; initial sTg: p = 0.0059). In multivariate logistic regression analysis, after adjusting for initial sTg levels, a DHU grade of 3 on PAWBS was an independent predictor of remission (PAWBS: p = 0.028; initial sTg <100 ng/ml: p = 0.043).In patients with iodine-avid distant metastases, intensity of DHU on 131I post-therapy scan correlated with subsequent percentage serum sTg reduction. Also, intense DHU could be one of the predictors of remission in these patients.
Keywords: Differentiated thyroid cancer; Distant metastasis; Diffuse hepatic uptake; 131I therapy; Treatment response

The aim of this study was to evaluate the potential of 18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) for monitoring the therapeutic efficacy of TAK-733, an inhibitor of mitogen-activated protein kinase kinase, in nude rats bearing A549 (human lung carcinoma) xenografts.TAK-733 was administered orally by gavage to nude xenograft rats for 2 weeks, at dosage levels of 0 (0.5 % w/v methylcellulose solution), 1, 3, and 10 mg/kg/day (n = 8/dose). Tumor size was measured before treatment (day 0), and on days 1, 3, 7, 9, 11, and 14. PET scans were performed pretreatment (day 0), and on days 2, 4, 7, 10, and 14. Tracer accumulations in tumor tissue were quantified as the mean standard uptake value (SUVmean).No deaths or treatment-related body weight losses occurred during the study period. TAK-733 showed dose-dependent inhibition of tumor growth and 18F-FDG uptake in tumor tissue. At a dosage of 10 mg/kg, TAK-733 treatment produced a statistically significant reduction in tumor weight from day 11 compared with the vehicle group (P < 0.05). Tumor growth was inhibited in the 10 mg/kg group with a treated/control value of 31 % on day 14. The SUVmean on day 2 in this dosage group was statistically lower than that observed on day 0, and that seen in the vehicle group on day 2 (P < 0.05 for both comparisons). Furthermore, this reduction in SUVmean at 10 mg/kg was maintained over time. In the two lower dosage groups (1 and 3 mg/kg), SUVmean gradually increased over time. 18F-FDG-PET enabled early determination of late anti-tumor activity in response to TAK-733 treatment.
Keywords: TAK-733; 18F-FDG-PET; MEK inhibitor; A549 xenograft rat

Concordance of positron emission tomography and computed tomography in patients with locally advanced gastric and esophageal cancer by Cemil Hocazade; Nuriye Özdemir; Ozan Yazici; Yakup Bozkaya; Doğan Yazılıtaş; Şerife Toptaş; Nurullah Zengin; Tağmaç Deren (621-626).
PET–CT is important for evaluating the cancer stage preoperatively. In patients with locally advanced disease, who are candidates for curative treatment modalities following computed tomography (CT) and ultrasonography evaluation, PET–CT can show distant metastases and spare patients unnecessary surgical interventions. We aimed to evaluate the contribution of PET–CT scans compared to conventional imaging studies on the change of treatment plan in patients with locally advanced esophagogastric cancer from neoadjuvant to palliative setting.In this study, 91 patients with histopathologically proven diagnosis of esophageal or gastric cancer in our clinic between the years 2010–2014 were included. Prior to PET–CT evaluation, all of the patients were evaluated with thorax and abdomen computed tomography. Seventy-six of these patients were further evaluated by PET–CT due to ambiguous findings on computed tomography and 15 of them for staging purposes. The patients, who were shown to have distant metastases on conventional radiological imaging, were excluded from the study population.Ninety-one patients were included in the study. Their median age was 57 (range 30–80) years and three-quarters of the patients were male. Most of the patients were evaluated by PET–CT due to suspicion of distant metastasis (83.5 %). Primary sites of the tumors on PET–CT were: esophagus 38.5 % and stomach 61.5 %. Between CT and PET–CT tumor stage and pathological lymphadenopathy concordance rates were 75.8, and 69.2 %, respectively. On PET–CT evaluation 47.3 % of patients had distant metastasis. New metastases were detected in 34.1 % of patients by PET–CT despite entering to scanning field of tomography. Following the PET–CT evaluation due to detected metastasis, 47.3 % of patients’ treatment plan was changed from neoadjuvant to palliative therapy.In the current study, 47.3 % (n = 43) of patients had distant metastasis that were not detected by CT evaluation. These patients were spared unnecessary surgical interventions. Evaluating the locally advanced gastric and esophageal cancer patients for PET–CT new metastasis could be indicated when the treatment plan of these patients would be changed from curative to palliative.
Keywords: Neoadjuvant; Gastric cancer; Esophageal cancer; Computed tomography; PET–CT

The clinical safety, biodistribution and internal radiation dosimetry of flutemetamol (18F) injection in healthy Japanese adult volunteers by Michio Senda; David J. Brooks; Gill Farrar; Edward J. Somer; Carolyn L. Paterson; Masahiro Sasaki; Brian J. McParland (627-635).
The Phase I safety, biodistribution and internal radiation dosimetry study in adult healthy Japanese males of flutemetamol (18F) injection, an in vivo β-amyloid imaging agent, is reported and compared with previously obtained Caucasian data.Whole-body PET scans of 6 healthy volunteers (age 51.8–61.7 years) were acquired approximately 4 h post-injection (administered activity 102–160 MBq). Venous blood sampling determined 18F activity concentrations in whole blood and plasma and high-performance liquid chromatography (HPLC) established the percentages of parent [18F]flutemetamol and its metabolites. Voided urine activity was recorded. The decay-corrected and normalised 18F activity of 14 source organ regions as a function of time was entered into the OLINDA/EXM software to calculate the internal radiation dosimetry and effective dose of each subject following the MIRD schema. The pharmacokinetics, biodistribution and dosimetry profiles were compared to data obtained from a cohort of healthy Caucasian adult volunteers from a previous Phase I study of [18F]flutemetamol.Flutemetamol (18F) injection was well tolerated. The highest mean initial uptakes were measured in the liver (15.2 %), lungs (10.2 %) and brain (6.6 %). The highest mean radiation absorbed doses were received by the gallbladder wall (366 μGy/MBq), upper large intestine (138 μGy/MBq) and small intestine (121 μGy/MBq). The mean effective dose was 34.9 μSv/MBq. HPLC analysis demonstrated that at 5-min post-injection about 75 % of plasma 18F radioactivity was in the form of parent [18F]flutemetamol, reducing to 8 and 2 % at 25 and 90 min, respectively, giving rise to less lipophilic 18F-labelled metabolites. Comparisons with the Caucasian cohort showed no differences that could be regarded as clinically significant.The clinical safety of [18F]flutemetamol demonstrated no differences of clinical significance in the pharmacokinetics, biodistribution and internal radiation dosimetry profiles between Caucasian and Japanese adults.
Keywords: Amyloid imaging; [18F]Flutemetamol; PET; Biodistribution; Dosimetry; Healthy Japanese subjects

The aim of this study was to determine the optimal reconstruction parameters on ordered-subset expectation maximization iterative reconstruction with resolution recovery, scatter and attenuation correction (OSEMRRSCAC) on 123I-FP-CIT SPECT in terms of the image quality, quantification and diagnostic ability.We evaluated the quality and quantification in 123I-FP-CIT SPECT images obtained by different reconstruction parameters using the anthropomorphic striatal phantom. The phantom images were acquired using a SPECT/CT system equipped with a low- and medium-energy general-purpose collimator and then were reconstructed using OSEMRRSCAC with various update numbers and the full width at half maximum (FWHM) of the Gaussian filter. The count ratio of the striatum, the coefficient of variation (CV) on the background and the specific binding ratio (SBR) were calculated to determine the optimal reconstruction parameters. Then, 42 consecutive patients who underwent 123I-FP-CIT SPECT were selected for clinical study. The patients were grouped into potentially decreasing group (20 with Parkinson’s disease, 5 with parkinsonian syndrome and 5 with dementia with Lewy bodies) and potentially normal binding group (4 with Alzheimer disease and 8 with essential tremor). Clinical images were reconstructed using OSEMRRSCAC and FBP with Chang’s AC (FBPAC). The performance of OSEMRRSCAC with the optimal reconstruction parameters was evaluated according to the receiver operating characteristic analysis and visual assessment.The count ratio increased with an increasing update number and converged uniformly with an update number over 90. The CV continuously increased with the update number. The SBR also increased with an increasing update number and converged uniformly with an update number of 90 or larger. The FWHM of the Gaussian filter influenced the image quality and quantification. In the clinical study, the area under curve (AUC) for the OSEMRRSCAC and FBPAC were 0.9812 and 0.9759, respectively. The quality of the SPECT images of OSEMRRSCAC (3.8 ± 0.8) was significantly superior to that of FBPAC (2.2 ± 0.7).We determined that the optimal reconstruction parameter for OSEMRRSCAC was 90 update numbers with 6.6 mm FWHM of the Gaussian filter. Our results suggested that the optimal reconstruction parameters have a potential to improve the performance and the image quality of 123I-FP-CIT SPECT in comparison with the FBP reconstruction.
Keywords: 123I-FP-CIT SPECT; Iterative reconstruction parameters; Resolution recovery; Scatter correction and attenuation correction

Assessment of 99mTc-MIBI SPECT(/CT) to monitor multidrug resistance-related proteins and apoptosis-related proteins in patients with ovarian cancer: a preliminary study by Seiji Kurata; Kimio Ushijima; Akihiko Kawahara; Hayato Kaida; Kouichirou Kawano; Yasumitsu Hirose; Masayoshi Kage; Toshiharu Kamura; Masatoshi Ishibashi; Toshi Abe (643-649).
Multidrug resistance (MDR) has been suggested to be a major cause of failure of chemotherapy treatment for cancer. It is associated with the expression of MDR-related and apoptosis-related proteins. Recently, technetium-99m hexakis 2-methoxyisobutylisonitrile (99mTc-MIBI) has been suggested as a tumor-seeking agent for the detection of MDR. The aim of this study was to evaluate 99mTc-MIBI single-photon emission computed tomography (SPECT)(/CT) for functional imaging of MDR-related and apoptosis-related proteins in patients with ovarian cancer.Eleven women (mean age 63 years, range 53–76) with a clinical suspicion of ovarian cancer were prospectively studied. All patients were examined with 99mTc-MIBI imaging before surgery. After intravenous injection of 740 MBq 99mTc-MIBI, SPECT(/CT) imaging at 10 min and 2 h was performed. Based on the semiquantitative analysis of 99mTc-MIBI SPECT(/CT), both early and delayed tumor uptake ratios and washout rate % were calculated. The expression of MDR-related and apoptosis-related proteins was assessed in surgically excised tumors. Immunohistochemical staining was performed to quantify the expression levels of multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein1 (MRP1), MRP3, lung resistance protein (LRP), breast cancer resistance protein (BCRP), Y-box-binding protein-1 (YB-1), Bcl-2, Bax and glutathione-S-transferase. 99mTc-MIBI imaging results and immunohistochemical results were compared.Laparotomy was performed in all patients. Six ovarian cancers were proven by histopathological examination. Five of the six ovarian cancers were positive for 99mTc-MIBI uptake on both early and delayed images with 99mTc-MIBI SPECT(/CT). MDR-related and apoptosis-related proteins were found to be expressed in all tumors. For the five positive 99mTc-MIBI uptake cases, the washout rate % of 99mTc-MIBI uptake showed a significant positive correlation with the expression of YB-1 (r = 0.988, P = 0.0015), and the early tumor uptake ratio showed a significant positive correlation with the expression of Bax (r = 0.882, P = 0.047).Our results suggested that 99mTc-MIBI SPECT(/CT) might be a valuable diagnostic imaging technique to evaluate MDR-associated YB-1 and Bax-mediated apoptosis in patients with ovarian cancer.
Keywords: 99mTc-MIBI; Ovarian cancer; Multidrug resistance; YB-1; Bax

The heart-to-mediastinum (H/M) ratio, the heart count normalized for the mediastinum count, is commonly used in cardiac 123I-metaiodobenzylguanidine (MIBG) imaging. However, there are reports describing age-dependent increases in the mediastinum count with or without correction for the injected dose (ID) and a poor correlation between the H/M ratio and heart count normalized for ID. We evaluated the validity of the mediastinum count as a reference in comparison with the ID.Results of cardiac 123I-MIBG imaging in 200 patients were analyzed. The mean counts for the heart and mediastinum were estimated to calculate the H/M ratio. Additionally, the heart and mediastinum counts were normalized for ID measured with a dose calibrator. ID was corrected for body size represented by body weight, body surface area, or lean body mass.The coefficient of variance of the ID-normalized mediastinum count was reduced by correcting ID for body size. The indicators of body size showed significant negative correlations with age. Although a positive correlation was found between age and the ID-normalized mediastinum counts, the age-dependence was reduced by body size correction. There was a close correlation between the H/M ratio and ID-normalized heart counts, and body size correction improved the correlation.The results of this study indicate the validity of the mediastinum as a reference region and support the use of the H/M ratio as an index of cardiac accumulation of 123I-MIBG.
Keywords: 123I-metaiodobenzylguanidine (MIBG); Heart-to-mediastinum (H/M) ratio; Quantitative evaluation; Injected dose