Iranian Journal of Nuclear Medicine
Volume:27 Issue: 2, Summer-Autumn 2019

Integration of single photon emission computed tomography (SPECT) and computed tomography (CT) scanners into SPECT/CT hybrid systems permit detection of coronary artery disease in myocardial perfusion imaging (MPI). Misregistration between CT and emission data can produce some errors in uptake value of SPECT images. The aim of this study was evaluate the influence of attenuation correction (AC) versus non-attenuation correction (NC) images and the effect of misregistration on all segments of SPECT images for quantitative and qualitative analysis. 99 patients (45 males, 54 females) underwent stress/rest myocardial perfusion imaging (MPI) using 99mTc-MIBI were used in this study. We also utilized cardiac insert and lung insert in cylinder phantom. Phantom studies were performed with and without defect. The misregistration of all patient data was measured and variation in misregistration of our population was recorded. The effect of attenuation correction (AC) and non-attenuation correction (NC) images were also evaluated in both phantom and patient data. The CT images were shifted by ±1, ±2, ±3 pixels along X-, Y- and Z-axis (Left/right, dorsal/ventral, cephalic/caudal) for both phantom and patient studies. Differences between misalignment data and misregistration correction images were also measured. Results displayed with 20 segments polar map analysis and illustration in standard orientations for cardiac tomographic images. In the patient population data, 1.5% were perfectly registered, 17% and 73% misaligned under 1 pixel and more than 1 pixel, respectively. AC of SPECT images showed increased uptake value in normal phantom and false positives findings were disappeared versus to NC images. In patient data, statistically significant variation were shown for the most segments before and after AC (P-value<=0.004) and also between AC of SPECT image and misregistration correction images (P-value<=0.048). Along X-axis, in 3 pixel shift in right direction, the percent of relative difference in lateral wall were 11.94% for mid anterolateral. Along Y-axis, the Ventral shift caused -15.9% changes in basal inferolateral and along Z-axis -8.59 % changes in apical anterolateral were also observed in caudal direction when 3 pixel shifts were used. This study showed that CT-based attenuation correction of cardiac images in hybrid SPECT/CT is important to improve image quality. Misalignment in caudal, cephalad, ventral and right direction introduced significant variation even in 1 pixel shift. It is important to apply misregistration correction even in small misalignment routinely in clinical myocardial perfusion imaging.

The ability of quadratic dose protocol to maintain a good quality image for an overweight and obese patient is well reported. However, a practical approach to the implementation of this protocol in whole-body imaging in Malaysia is currently lacking. Hence, the aim of this study is to derive the quadratic dose formula that suits our PET system. Whole-body PET imaging protocol was performed using NEMA 2012/IEC 2008 phantom. Two dose protocols were adhered, namely linear and quadratic dose protocol. A PET Discovery ST, which is BGO-based PET system was used in this study. This study was guided by technical guidelines published by Koopman et al. Finally, a comparative analysis between the effective dose yielded by linear and quadratic dose protocols was performed. Implementation of quadratic dose protocol using our PET system lengthen the scanning time to 226 s, as compared to 150 s currently used in the linear dose protocol. Meanwhile, the findings revealed that the quadratic dose protocol led to a greater effective dose for the body weight of 62 kg and above. These findings were observed in all the five groups of patient studied. In conclusion, a successful trial of the quadratic dose protocol on our PET system has been established. Despite the long acquisition time and greater effective dose, implementation of quadratic dose protocol is necessary for better quantification of the image, as well as ensuring constant image quality across all patients, especially overweight and obese patients.

The gamma cameras, based on scintillation crystal followed by an array of photomultiplier tubes (PMTs), play a crucial role in nuclear medicine. The use of square PMTs provides the minimum dead zones in the camera. The camera with square PMTs also reduces the number of PMTs relative to the detection area. Introduction of a positioning algorithm to improve the spatial resolution in the detector with square PMT have been of interest in recent years. In this study, the maximum-likelihood and correlated signal enhancement positioning methods were implemented in a camera with square PMTs. The developed camera consists of 3/8” thick monolithic NaI(Tl) crystal coupled to the array of 76mm sized PMTs. The comparison is based on measuring full width at half maximum (FWHM) and standard deviation of FWHM of point sources in a 15×15 grid of samples with 2-mm grid spacing, produced using MLE and CSE positioning methods. The intrinsic spatial resolution in (x, y) directions was (3.8, 3.8), (4.3, 4.5) mm for CSE and MLE methods respectively. Also, the standard deviations was almost the same in both methods (0.5 and 0.6 for CSE and MLE respectively). Although by applying MLE method, the resolution degrades by 16% but the produced image introduced acceptable quality. The results show the MLE method presented acceptable performance in comparison to CSE method as reference in the detector with large square PMTs. Note that the MLE method does not require any linearity correction process because it can estimate the exact position of events.

Recently, 166Ho-BPAMD was introduced as a suitable agent for bone marrow ablation. The aim of this study was to estimate the absorbed dose of this novel agent in the human organs which is necessary before the clinical application. 166Ho was produced by direct irradiation of 165Ho in the research reactor. 250 µg of BPAMD was added to the vial containing 111 MBq of 166Ho and the pH of the reaction mixture was adjusted to 6 while it was incubated for 45 min at 90-100°C. The strong cation exchanger was applied to improve the radiochemical purity checked by ITLC method. 166Ho-BPAMD was injected to male Syrian rats and the uptake in different organs was assessed. The absorbed dose in human organs was estimated following the mass extrapolation and according to RADAR method. 166Ho-BPAMD was prepared with the radiochemical purity of higher than 96%. After injection to male Syrian rats, the most of the activity was observed in the bone tissues. Bone surface and bone marrow received the highest amounts of the absorbed dose with the value of 0.916 and 0.647 mGy/MBq, respectively. Bone marrow to the bone tissue and total body absorbed dose ratio for 166Ho-BPAMD was comparable to the other bone seeking radiopharmaceuticals. 166Ho-BPAMDdelivers safe and reasonably appropriate dose to the human organs and can be considered as a novel bone marrow ablative agent.

99mTc-Methylene diphosphonate (99mTc-MDP) three phase bone scintigraphy (TPS) is beneficial to evaluate the success of femoral head revascularization using novel distraction osteogenesis techniques with bone muscle pedicle grafts. This pilot study was undertaken to evaluate the feasibility and utility of 99mTc-MDP three phase bone scintigraphy in predicting outcome in patients with femoral avascular necrosis (Ficat staging 2 or 3) using a new surgical technique and external fixator device as part of the distraction osteogenesis technique. We also wanted to find out if bone scan can determine the timing of removal of bone distracters and thus improve the clinical outcome. 39 newly diagnosed patients with femoral AVN underwent a new modified Iliazaro technique in a nearby specialised Orthopaedic centre. 40 hips with Ficat and Arlet stage II and III in the age group of 18 to 33 years were included (Male: Female = 38: 01). Necessary clearance from institutional review board was obtained. Patients were assessed both subjective and objectively for the presence of pain (Harris Hip score), range of movements, radiological and TPS findings of the affected hip joints. TPS of hip joints was performed pre and postoperatively using 15 mCi of 99mTc-MDP intravenously. Patients who did not show improvement in bone scan at 6th week had follow up scans at 10th and 14th week respectively. Radiographic correlation was also obtained. Clinical and TPS imaging data were analysed.Clinical scoring (Harris hip score, HHS) was done pre and postoperatively in all patients. TPS demonstrated good improvement in cortical blood flow to the femoral head after revascularization at 6 weeks in 30 out of 40 hips ( i.e. 75%) using this new surgical technique and fixator device. 7 patients showed improvement at 10th week and remaining 2 patients showed no improvement even at 14th week post-surgery. Quantitation was also performed to substantiate the visual findings using perfusion index(PI), initial uptake ratio (IUR) in soft tissue phase image and delayed uptake ratio (DUR) in skeletal phase image in all patients. Patients demonstrated significant improvement in Postop DUR when compared to preop. DUR values. HHS improved from 57 to 83 in 75% patients postoperatively indicating a good success of this surgical technique. All the data was analysed using SPSS software version. Statistical significance was accepted when p<0.05. TPS is a simple, reliable and cost effective investigation in the non-invasive assessmentof distraction osteogenesis in AVN patients using this novel technique of corticostomy and gluteus medius pedicle graft at greater trochanter.It is a good tool to assess new bone formation. Intensity of MDP uptake at affected femoral head is a marker of restored metabolism and can be effectively used in timing the removal of bone distracters which is usually 6 weeks in majority of cases.

A low iodine diet (LID) is recommended prior to the Radioactive Iodine-131 (RAI) treatment or scanning in differentiated thyroid carcinoma (DTC) post total thyroidectomy. However, recommended strictness of LID is varying among major guidelines. This study was aim to investigate the patient’s compliance to LID by measuring the urinary iodine level post LID. A total of one hundred and four patients of DTC post total thyroidectomy patients that were planned for treatment or scanning were enrolled into the study. 55 patients are subjected to 1-week strict LID while the other 49 patients are subjected to 1-week non-specified LID before RAI administration. Baseline urinary iodine level were obtained prior to the LID and second urinary iodine level were measured at day-8 or prior to RAI administration. The compliance rate of patients that achieved urinary iodine level less than 100ug/L following 1-week strict LID was 89.1% as for the 1-weeks non-specified LID was 91.8% which did not show any significant difference between the two LID group (p=0.746). After 7 days institution of non-specified LID, the mean urinary iodine level was significantly reduced about 40.8% compared to strict LID (36.3%). The 1 week of non-specified LID is effective enough to decrease the urinary iodine level in low iodine intake area and the longer duration of LID is more hindrance for the patient to comply.

The position estimation in gamma detection system will have constant misplacements which can be corrected in the calibration procedure. In the pixelated crystal uniformly irradiation of detector will produce irregular shape due to position estimation errors. This image is called flood field image and is used to calibrate the position estimation. In this work we present a novel approach to automatically calibrate pixelated crystal array position estimation. In the flood image of a pixelated crystal array the local peaks represent the estimation of position for the gamma photons that interacted in a single crystal pixel. First, the method detects 2-D peak locations automatically in the case of blurred pixel responses in the presence of noise and disturbance of the image. The algorithm consists of a filtering step for smoothing the image followed by two rounds of local peak detection. After localizing image peaks, the correction routine will map the image locations to the crystal pixels using the thin-plate spline interpolation method. The algorithm is tested for two flood images obtained from developed detector with different irregularity levels. By configuring constant parameters according to the detector configuration the method detected all crystal pixels in the image and map them correctly. The method further has been tested for10 identical blocks and the result showed automatic peak detection routine for all the blocks. An automatic peak detection is presented to work instead of time consuming manual calibration routines. The method shows robust performance in the presence of image noise.

Eating fatty food is a common technique for decreasing extra cardiac activity, but sometimes patients refuse to eat fatty foods due to various reasons during myocardial perfusion imaging. The aim of this study is to introduce an alternative method for patients who are not able to use fatty foods to accelerate the transit of radiotracer from the liver. A total of 100 patients were randomized into four groups to take 200 cc of lemon juice, 200 cc of pomegranate juice, 200 cc of secanjabin, and 100 mg of fatty meal, 10 min after injection of 20 mCi 99mTc-MIBI, respectively in groups A, B, C, and D. The study is carried out in both rest and stress imaging at 30 and 50 min post-injection. Using ROI- based analysis, means of activity counts in heart and liver and, then the mean of heart/liver (H/L) ratios were calculated. According to data analysis of both rest and stress imaging at min 30 and 50, A and D groups had significantly higher H/L ratio than groups B and C. Comparing the images of groups in both rest and stress protocol at minutes 30 and 50, A and D groups had significantly higher H/L ratio at 50 minutes in comparison with 30 minutes. In patients who refrain from eating fatty foods, drinking of diluted lemon juice may be recommended as a simple technique and the best alternative to decrease extra-cardiac activity and increase the H/L ratio.

Bifunctional radiosensitizer agents in which nitroaromatic moieties are attached through a linker to antineoplastic moieties have demonstrated higher cytotoxicity and radiosensitizer effects than the corresponding counterparts. This study was conducted to investigate the cytotoxicity and radiosensitizer activities of 2, 4-dinitrobenzene as a radiosensitizer moiety which connected to α, β unsaturated aryl ketones against the radioresistant human HT29 colon cancer cells. A series of bifunctional radiosensitizer derivatives that are composed of electron-affinic 2, 4-dinitrophenyl moiety and thiol reactive unsaturated conjugated ketones were prepared. The designed compounds were synthesized by the reaction of the corresponding 2, 4-dinitrobenzaldehyde, cyclohexanone and different aryl aldehydes. The cytotoxicity and radiosensitizer activity of the tested compounds were examined against HT29 colon cancer cells under aerobic condition. The IC50 value of the tested compounds and percent of survival cells were analyzed by the MTT assay. The clonogenic assay was used to assess the cell viability following treatment with the tested compounds with or without the combination of radiation. This approach demonstrated that the tested compounds at the concentrations utilized have little or no cytotoxicity towards the radioresistant HT29 cell line but have great cytotoxicity and radiosensitizer activity when combined with irradiation. The novel bifunctional unsaturated conjugated aryl ketones which are thiol alkylators found to exhibit radiosensitivity activity. Consequently, these new developed compounds should be evaluated further to assess their potential efficacy with radiotherapy to combat malignancies in a pre-clinical animal model.

The choice of optimal radionuclides for radioimmunotherapy depends on several factors, especially the radionuclide and antibody. The dosimetric characteristics of a non-internalizing and an internalizing monoclonal antibody (MAb) labeled with beta emitting radionuclides were investigated. Using Geant4-DNA Monte Carlo simulation, we carry out dosimetric calculations for different subcellular distributions of beta-emitting radionuclides; 131I, 177Lu, 64Cu, 186Re and 153Sm. The dependency of theradialdose profiles on the energy spectra of   electrons (beta particles and Auger and internal conversion electrons) and also their relative yield of emission is clear. The highest difference between the radionuclides tested was observed when the activity was localized in the nucleus. There was not considerable difference in the nucleus dose when radionuclides were localized in cytoplasm and over the cell membrane. There is a very significant increase in the dose deposited to the nucleus if 153Sm localized at the nucleus. Although subcellular localization of activity isn’t a critical factor for beta emitting radionuclides, but the use of internalizing MAbs leads to an increase in nucleus dose and to the killing of single cells in addition to the tumors.

A 34 year old woman with malaise, polyuria and nocturia as well as nausea and vomiting referred to perform a thyroid scan due to right thyroid lobe mass. The scan showed a cold nodule in the right thyroid lobe. Serum calcium of 16.9, serum phosphorus of 1.8 and PTH of 1156 were noticed in laboratory tests. Parathyroid scan with 99mTc-MIBI showed no abnormal tracer activity in the neck and mediastinum in planar and SPECT images. The patient underwent surgery and histopathology confirmed parathyroid carcinoma. To extent of our knowledge, this is one of few cases of negative 99mTc-MIBI uptake parathyroid carcinoma were reported.

Localization of 99mTc- hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) by parathyroid adenomas is well known, and this warrants MIBI scan to evaluate suspected parathyroid adenoma in primary hyperparathyroidism. Typically, the radionuclide concentrates in both the thyroid gland and parathyroid adenoma in early images, and later on delayed images washes out slowly from the parathyroid adenomas located in the neck or mediastinum, in comparison with more rapid wash out from the thyroid gland. We report a 71-year old woman with history of hypothyroidism, who has been on levothyroxine therapy for 5 years, and primary hyperparathyroidism, for which a double phase 99mTc-MIBI parathyroid scintigraphy was performed. Although the planar views demonstrated no evidence of radiotracer uptake in thyroid gland, single photon emission computed tomography/computed tomography (SPECT-CT) images revealed the presence of thyroid gland with a multinodular pattern on CT component of the study. Also planar images showed no focal uptake, but in SPECT-CT evaluation a MIBI-avid nodule was depicted in the posteromedial aspect of lower portion of left thyroid lobe, representing a parathyroid adenoma, later confirmed by pathology after surgical resection. The possible explanation for non-visualization of thyroid gland could be thyroid suppression with levothyroxine.

We report a case of Hodgkin lymphoma (classic type) referred for response assessment after two cycles of chemotherapy with ABVD regiment. The F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET/CT) showed hypermetabolic cutaneous and subcutaneous lesions with a linear pattern in the left arm with significant F-18 fluorodeoxyglucose positron accumulation in associate with left axillary hypermetabolic lymph nodes. She presented with left arm pruritic rash accomplished by pain from two weeks ago. On clinical examination, painful papulovesicular rash with palpable enlarged axillary lymph node were noted. These findings were compatible with cutaneous herpes zoster infection of the left arm along with axillary reactive lymphadenopathy.

Post-treatment or diagnostic whole-body radioiodine scintigraphy is widely used to assess the residual, recurrence, or metastases of differentiated thyroid carcinoma because of the high sensitivity and accuracy that this assessment provides. While bearing in mind all the diagnostic potential of this test, we have to consider its’ potential pitfalls, as well. Herein, we present 4 patients with differentiated thyroid carcinoma, who received 131I for ablation therapy after having undergone total thyroidectomy. On post-treatment radioiodine scintigraphy, foci of unusual 131I uptake were noted in facial, axillary, inguinal, and renal regions, which were finally either histologically or anatomically diagnosed as papillary oncocytic cystadenoma, ectopic axillary breast tissue, epidydimal cyst, and simple renal cyst, respectively. Such 131I uptake patterns underscore the value of recognizing where and why false-positive uptakes take place and should appreciate the potential causes of false-positive results in whole-body 131I scintigraphy.