Lymphocyte/mean platelet volume ratio, a new marker; is it effective in predicting the prognosis of COVID-19 cases?

OBJECTIVES: This study aims to determine the prognostic significance of the lymphocyte/mean platelet volume ratio (LMR) in terms of the clinical course of the disease in patients with COVID-19. METHODS: Patients over 18 who were evaluated for COVID-19 during the period from April 1, to April 30, 2020 were retrospectively scanned. Patients with at least 1 positive PCR test result were as assigned to Group 1 while patients with negative test results were assigned to Group 2. The LMR ratio was calculated by dividing the lymphocyte value by that of MPV. The relationship between LMR, severity of patients' CT findings and 28-day mortality was evaluated. RESULTS: A total of 938 patients were included in the study. It was observed that the lymphocyte and LMR levels were significantly different in those who died within 28 days (p < 0.001, p ≤ 0.001). In the ROC analysis for the LMR level, the area under the curve (AUC) was found to be 0.737 (95% CI 0.639‒0.834). When the cut­off value of LMR was 0.045, the sensitivity was found to be 99.0 % and specificity was 15.2 %. CONCLUSION: LMR can be a guide in multiple cases of care provided to critical patients, as is the case in the COVID-19 pandemic and can be used in recognizing critical patients (Tab. 5, Fig. 1, Ref. 21).

Analysis of posterior circulation diameters depending on age, sex and side by computed tomography angiography.

BACKGROUND: Posterior circulation of brain is important because of vital organs' blood supply provided by them. In this study, we evaluate the relationship of posterior circulation measurements with age, gender and side by using computed tomography angiography (CTA) images. MATERIALS AND METHODS: A total 199 brain CTA examinations were retrospectively analysed for all posterior circulation arteries (vertebral artery, basilar artery, posterior cerebral artery [PCA], superior cerebellar artery [SCA], anterior inferior cerebellar artery, and posterior inferior cerebellar artery [PICA]) to compare the difference based on age, gender and side. RESULTS: There is no correlation between age and the mean diameters of all vessels (p > 0.05). The mean diameter of left vertebral artery was higher than right vertebral artery in all genders (p = 0.004 for males and p < 0.001 for females). The mean diameter of left SCA and PICA were higher than right SCA and PICA in females (p = 0.032 and p = 0.027, respectively). The mean diameters of basilar, left PCA, left SCA, left vertebral, right PCA, right SCA, right PICA and right vertebral artery were higher in males and that differences were statistically significant (p < 0.001, p = 0.002, p = 0.006, p = 0.004, p = 0.001, p = 0.003, p = 0.002, and p = 0.006, respectively). CONCLUSIONS: The posterior circulation vessel diameter is not affected by aging. The mean diameters of basilar artery, both PCAs, both SCAs, right PICA, both vertebral arteries were higher in males. The mean diameter of left vertebral artery is higher than that of right vertebral artery in all genders.

Relationship of vascular variations with liver remnant volume in living liver transplant donors.

BACKGROUND: In this study, we investigated the relationship between the portal vein and hepatic artery variations and the remaining liver volume in living donors in liver transplantation. MATERIALS AND METHODS: In the study, triphasic abdominal computed tomography images of 180 live liver donor candidates were analysed retrospectively. Portal veins were divided into four groups according to the Nakamura classification and seven groups according to the Michels classification. The relationship between vascular variations and remnant liver volume was compared statistically. RESULTS: According to the Nakamura classification, there were 143 (79.4%) type A, 23 (12.7%) type B, 7 (3.9%) type C and 7 (3.9%) type D cases. Using the Michels classification, 129 (71%) type 1, 12 (6.7%) type 2, 24 (13%) type 3, 2 (2.2%) type 4, 10 (5.6%) type 5, 1 (0.6%) type 6, and 2 (1.1%) type 7 cases were detected. There was no significant difference in the percentage of the remaining volume of the left liver lobe between the groups (p = 0.055, p = 0.207, respectively). CONCLUSIONS: Variations in the hepatic artery and portal vein do not affect the remaining liver volume in liver transplantation donors.

Utility of biochemical markers and RVD/LVD ratio in acute pulmonary embolism risk classification in Emergency Department.

OBJECTIVE: We aimed to determine the efficacy of troponin I, D-dimer, and lactate levels and right ventricular diameter (RVD)/left ventricular diameter (LVD) ratio on pulmonary computed tomography angiography (PCTA) in the risk classification of patients who were diagnosed with acute pulmonary embolism (APE) in Emergency Department (ED). PATIENTS AND METHODS: Patients who were diagnosed as having APE by PCTA in ED were included in this retrospective study. Patients were grouped as high-risk (undergoing cardiopulmonary resuscitation or given thrombolytic therapy), moderate-risk (with non-high-risk and positive ECO findings) and low risk (others). Troponin I, D-dimer, and lactate levels of patients were determined. RVD, RVD/LVD ratio, and interventricular septum deviation were calculated from PCTA images. RESULTS: A total of 121 patients were included (35 high, 36 moderate, 50 low risk). Lactate was different in the high-risk group from the other groups, whereas there was no difference between the moderate and low-risk groups. Troponin I levels were not different between the high-risk and moderate-risk groups. There were statistically significant differences between the high, moderate, and low-risk groups in terms of mean RVD/LVD ratios. ROC analyses performed in order to define high-risk group revealed a cut-off value of > 2.3 (AUC = 0.848, sensitivity = 70%, specificity = 90%, + Likelihood ratio (LR) = 7, -LR = 0.33, 95% CI = 0.752-0.943) for lactate and > 1.40 (AUC = 0.695 sensitivity = 71%, specificity = 80%, + LR = 3.6, -LR = 0.36, 95% CI = 0.668-0.822) for RVD/LVD ratio. CONCLUSIONS: Lactate levels and RVD/LVD ratio were shown to be useful in distinguishing high-risk patients from other patient groups. Troponin I is important in terms of showing cardiac involvement, but it is inadequate in distinguishing between high and moderate-risk patients. Lactate, troponin I, and RVD/LVD ratio may be used together for a more accurate separation of patients with high, intermediate and low-risk.

Diagnostic value of copeptin in acute myocardial infarction.

OBJECTIVE: The aim of this study was to investigate the effectiveness of copeptin in the early diagnosis of acute myocardial infarction (AMI), and to compare the diagnostic efficacy of copeptin with other cardiac markers. PATIENTS AND METHODS: A total of 160 cases were enrolled in the study. All were over 18 years of age, and consisted of 54 non-ST elevation MI (NSTEMI), 54 ST segment elevation MI (STEMI), and 52 healthy subjects (controls). Serum troponin-I, CK-MB mass, copeptin and CRP levels were measured in each of the cases, and were compared between the three groups for statistical differences. RESULTS: The copeptin levels in the STEMI (p < 0.001) and NSTEMI (p = 0.042) groups were found to be significantly higher than the control group. Spearman's correlation analysis showed a significant positive correlation between the level of copeptin and the presence of AMI (r = 0.285, p < 0.001), CK-MB mass (r = 0.246, p = 0.002), and troponin-I (r = 0.199, p = 0.012). Sensitivity, specificity, and AUC values of the tests, according to ROC analysis performed for the diagnosis of AMI were; troponin-I > 0.1 ng/mL (71.0%, 100.0%, and 0.855); CK-MB mass > 3.59 ng/mL (77.8%, 92.3%, and 0.911); CRP > 6.37 mg/L (53.7%, 88.5%, and 0.769); and copeptin > 2.47 ng/mL (66.7%, 75.0%, and 0.676), respectively (p < 0.001). CONCLUSIONS: Cardiac troponin remains the gold standard biomarker for the diagnostic evaluation of AMI. Copeptin can be used as a diagnostic marker in patients with suspected AMI in combination with other biomarkers, but, copeptin alone should not be considered as a single diagnostic marker in patients with suspected AMI.

Evaluation of Radiation Exposure to Staff and Environment Dose from [18F]-FDG in PET/CT and Cyclotron Center using Thermoluminescent Dosimetry.

BACKGROUND: PET/CT imaging using [18F]-FDG is utilized in clinical oncology for tumor detecting, staging and responding to therapy procedures. Essential consideration must be taken for radiation staff due to high gamma radiation in PET/CT and cyclotron center. The aim of this study was to assess the staff exposure regarding whole body and organ dose and to evaluate environment dose in PET/CT and cyclotron center. MATERIALS AND METHODS: 80 patients participated in this study. Thermoluminescence, electronic personal dosimeter and Geiger-Muller dosimeter were also utilized for measurement purpose. RESULTS: The mean annual equivalent organ dose for scanning operator with regard to lens of eyes, thyroid, breast and finger according to mean±SD value, were 0.262±0.044, 0.256±0.046, 0.257±0.040 and 0.316±0.118, respectively. The maximum and minimum estimated annual whole body doses were observed for injector and the chemist group with values of (3.98±0.021) mSv/yr and (1.64±0.014) mSv/yr, respectively. The observed dose rates were 5.67 µSv/h in uptake room at the distance of 0.5 meter from the patient whereas the value 4.94 and 3.08 µSv/h were recorded close to patient's head in PET/CT room and 3.5 meter from the reception desk. CONCLUSION: In this study, the injector staff and scanning operator received the first high level and second high level of radiation. This study confirmed that low levels of radiation dose were received by all radiation staff during PET/CT procedure using 18F-FDG due to efficient shielding and using trained radiation staff in PET/CT and cyclotron center of Masih Daneshvari hospital.

Electron microscopic examination of the effects of methyl parathion exposure on the ovaries.

OBJECTIVE: In our study, we aimed to investigate histopathological effects of chronic methyl parathion exposure on ovaries at electron microscopic level. MATERIALS AND METHODS: In this study, Wistar albino type, adult, female rats with an average weight of 190-250 g were used. 30 female rats, included in this study, were divided into 3 groups. Group I received only saline and was evaluated as the control group, whereas Group II received 1/50 percent of LD50 dose of methyl parathion and Group III received 1/20 percent of LD50 dose of methyl parathion every day at 130 pm orally by gavages during two estrus cycles (8 days). The rats at proestrus stage on the morning of 9th day of the study underwent bilateral ovariectomy. Ovarian tissues of the control and drug groups were examined under the electron microscope; primordial and growing follicles were included in the evaluation, however, corpora lutea were excluded taking into account the presence of remaining regressive corpora lutea from the previous cycles. RESULTS: Following examination of ovarian tissues of rats exposed to 1/50 and 1/20 percent of LD50 dose of Methyl parathion at electron microscopic level, it was detected that significant structural changes had occurred in developing follicles and ovarian stroma in both drug groups, and that primordial follicles had not been affected significantly from methyl parathion but necrosis had been developed in oocyte and granulosa cells of developing follicles, and that in 1/20 group in addition to these changes, apoptotic changes had been found in granulosa cells of developing follicles. CONCLUSIONS: As a result of chronic exposure to methyl parathion, rat ovaries are significantly affected and follicular development is impaired. This state may explain the cause of infertility due to chronic pesticide exposure.

Evaluation of Device-associated Nosocomial Infections in a Paediatric Intensive Care Unit.

OBJECTIVE: The aim of this study was to evaluate the rate of device-associated healthcare-associated infections (DA-HAI) in a paediatric intensive care unit (PICU). In addition, the identities of the responsible micro-organisms and of their antibiotic sensitivities were determined. SUBJECTS AND METHODS: Patients who had been treated and followed-up in a PICU for more than 48 hours between January 2008 and December 2013 were included in the study. Device-associated nosocomial infections were defined by the Centers for Disease Control (CDC) criteria. RESULTS: Nosocomial infections were detected in 244 of the 7376 patients over the six-year period. A diagnosis of DA-HAI was made in 75 (30.7%) of these infections. The rates of device utilization were 26% for mechanical ventilators, 6% for central venous catheters and 0.9% for urethral catheters. The rate of device-associated infections was 30.7%, and their frequency was 1.9/1000 patient-days. The device-associated nosocomial infection rates for mechanic ventilators, central and urethral catheters were 5.6, 1.62 and 3.77 per 1000 patient-days, respectively. Of these infections, Pseudomonas aeruginosa was the most frequent pathogen. Patients who developed hospital infections had longer durations of ICU hospitalizations and more often had to use mechanical ventilators and central and urinary catheters. CONCLUSIONS: The duration of hospitalization and the use of mechanical ventilators and central and urinary catheters were related to the increases in nosocomial infections. Therefore, target-oriented active surveillance should be regularly performed, and the superfluous employment of invasive devices should be avoided.

Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu2(BO3)2.

The temperature dependence of the gapped triplet excitations (triplons) in the 2D Shastry-Sutherland quantum magnet SrCu(2)(BO(3))(2) is studied by means of inelastic neutron scattering. The excitation amplitude rapidly decreases as a function of temperature, while the integrated spectral weight can be explained by an isolated dimer model up to 10 K. Analyzing this anomalous spectral line shape in terms of damped harmonic oscillators shows that the observed damping is due to a two-component process: one component remains sharp and resolution limited while the second broadens. We explain the underlying mechanism through a simple yet quantitatively accurate model of correlated decay of triplons: an excited triplon is long lived if no thermally populated triplons are nearby but decays quickly if there are. The phenomenon is a direct consequence of frustration induced triplon localization in the Shastry-Sutherland lattice.

The relationship between blood lactate, carboxy-hemoglobin and clinical status in CO poisoning.

AIM: We aimed to determine the relationship between blood lactate, carboxy-hemoglobin (COHb) levels and the severity of clinical findings in patients with CO poisoning. PATIENTS AND METHODS: Patients over 18 years old and of both gender who were admitted to Emergency Department with the diagnosis of CO poisoning between 10.02.2008 and 17.03.2011 were enrolled in this study. Detailed physical examination of each patient was performed, patients and their relatives were informed about the study and written consents were noted. The levels of consciousness, physical examination findings, electrocardiographic findings, Glasgow Coma Scale (GCS) scores, laboratory results (lactate, COHb, CK-MB, Troponin-I levels) and applied treatments [normobaric oxygen therapy (NBOT), hyperbaric oxygen therapy (HBOT)] were recorded to standart data entry form for each patient. "SPSS for Windows version 18" package program was used for statistical analysis of the data. RESULTS: Total 201 patients were included in this study. Thirty five patients (17.4%) received HBOT and lactate; COHb, CKMB, Troponin-I levels of this group were higher than the other patients. Lactate and COHb levels were statistically significantly higher in patients with GCS < 15 than the ones with GCS = 15 (p < 0.01). The patients whose both Troponin-I and CK-MB levels increased have higher lactate levels (p = 0.038), but COHb levels of these patients did not change (p = 0.495). CONCLUSIONS: According to our study, blood lactate and COHb levels were both correlated with the changes of consciousness in CO poisoning. Blood lactate levels together with COHb in defining indications for HBO treatment might be suggested.

The evaluation of serum N-terminal prohormone brain-type natriuretic peptide, troponin-I, and high-sensitivity C-reactive protein levels in children with congenital heart disease.

Although advanced diagnostic and treatment methods are available, congenital heart disease (CHD) holds an important place among the causes of death within the first year of age. Therefore, several prognostic factors are needed for diagnosis and monitoring of these patients. In this study, which includes 66 CHD patients and 38 healthy control children, serum cardiac troponin-I (cTnI), high-sensitivity C-reactive protein (Hs-CRP), and N-terminal prohormone brain-type natriuretic peptide (NT-proBNP) levels were analyzed for their prognostics values. The patient groups were categorized and then evaluated as cyanotic (n = 16), acyanotic (n = 50), symptomatic (n = 23), asymptomatic (n = 43), and isolated ventricular septal defect (VSD)-isolated atrial septal defect (ASD) groups. Cyanotic group was statistically compared with acyanotic group, symptomatic group with asymptomatic group, and VSD group with ASD group. Between the cyanotic, acyanotic, and control groups; between symptomatic and asymptomatic groups; and between the VSD and ASD groups, significant difference was not showed for age (p > 0.05). NT-proBNP was found to be significantly higher in the cyanotic group than acyanotic and control group, in the symptomatic group than asymptomatic group; and in the patient group than healthy control group (p < 0.05). Between the groups of VSD and ASD, significant difference was not showed (p > 0.05). The same comparison results for TnI and Hs-CRP were not significant (p > 0.05). TnI and Hs-CRP were only found significantly higher in the patient group than healthy control group (p < 0.05). Eventually, we think that NT-proBNP, Hs-CRP, and TnI might be used for clinical management and estimation of outcome of these disorders in the future and these also might be able to modify existing strategies, but much more studies are needed.

Acute-phase reactants and cytokines in ischemic stroke: do they have any relationship with short-term mortality?

BACKGROUND: Many unknown risk factors play a role in the etiopathogenesis of stroke. The appearance of inflammatory cells within the damaged tissue after cerebral ischemia suggests that an inflammatory response may play a role in stroke pathogenesis. In our study, we examined whether an association exists between the acute-phase reactants and the levels of cytokines, the volume and diameter of the stroke, and short-term mortality in patients who were diagnosed as acute ischemic a stroke after admission to the Emergency Department. PATIENTS AND METHODS: A total of 50 consecutive patients who applied to the Emergency Service with acute ischemic stroke were enrolled in the study. Their stroke volume were calculated and serum samples were obtained as soon as they arrived into the Emergency Service. The patients were evaluated according to the Glasgow Coma Scale (GCS) and National Institutes of Health Stroke Scale (NIHSS). RESULTS: There was no significant correlations between stroke volume and levels of cytokine and acute-phase reactants in dead patient group or in living patient group. A correlation and statistical significance was found between stroke volume and hospital stay time in living patient group. In addition, GCS and NIHSS scores were correlated with stroke volume and was found a significant statistically. CONCLUSIONS: Scales such as GKS and NIHHS, which evaluate the functional state of patients, are the best indicators for defining prognosis in our daily practices. In addition, we found a positive correlation between levels of CRP (C reactive protein) and prognosis. However, we did not observe a statistically significant correlation between prognosis and other acute-phase reactants such as TNF-alpha, IL-6, IL-8, IL-10, fibrinogen, and leukocytes.

K-edge ratio method for identification of multiple nanoparticulate contrast agents by spectral CT imaging.

OBJECTIVE: Recently introduced energy-sensitive X-ray CT makes it feasible to discriminate different nanoparticulate contrast materials. The purpose of this work is to present a K-edge ratio method for differentiating multiple simultaneous contrast agents using spectral CT. METHODS: The ratio of two images relevant to energy bins straddling the K-edge of the materials is calculated using an analytic CT simulator. In the resulting parametric map, the selected contrast agent regions can be identified using a thresholding algorithm. The K-edge ratio algorithm is applied to spectral images of simulated phantoms to identify and differentiate up to four simultaneous and targeted CT contrast agents. RESULTS: We show that different combinations of simultaneous CT contrast agents can be identified by the proposed K-edge ratio method when energy-sensitive CT is used. In the K-edge parametric maps, the pixel values for biological tissues and contrast agents reach a maximum of 0.95, whereas for the selected contrast agents, the pixel values are larger than 1.10. The number of contrast agents that can be discriminated is limited owing to photon starvation. For reliable material discrimination, minimum photon counts corresponding to 140 kVp, 100 mAs and 5-mm slice thickness must be used. CONCLUSION: The proposed K-edge ratio method is a straightforward and fast method for identification and discrimination of multiple simultaneous CT contrast agents. ADVANCES IN KNOWLEDGE: A new spectral CT-based algorithm is proposed which provides a new concept of molecular CT imaging by non-iteratively identifying multiple contrast agents when they are simultaneously targeting different organs.

Evaluation of whole-body MR to CT deformable image registration.

Multimodality image registration plays a crucial role in various clinical and research applications. The aim of this study is to present an optimized MR to CT whole-body deformable image registration algorithm and its validation using clinical studies. A 3D intermodality registration technique based on B-spline transformation was performed using optimized parameters of the elastix package based on the Insight Toolkit (ITK) framework. Twenty-eight (17 male and 11 female) clinical studies were used in this work. The registration was evaluated using anatomical landmarks and segmented organs. In addition to 16 anatomical landmarks, three key organs (brain, lungs, and kidneys) and the entire body volume were segmented for evaluation. Several parameters--such as the Euclidean distance between anatomical landmarks, target overlap, Dice and Jaccard coefficients, false positives and false negatives, volume similarity, distance error, and Hausdorff distance--were calculated to quantify the quality of the registration algorithm. Dice coefficients for the majority of patients (> 75%) were in the 0.8-1 range for the whole body, brain, and lungs, which satisfies the criteria to achieve excellent alignment. On the other hand, for kidneys, Dice coefficients for volumes of 25% of the patients meet excellent volume agreement requirement, while the majority of patients satisfy good agreement criteria (> 0.6). For all patients, the distance error was in 0-10 mm range for all segmented organs. In summary, we optimized and evaluated the accuracy of an MR to CT deformable registration algorithm. The registered images constitute a useful 3D whole-body MR-CT atlas suitable for the development and evaluation of novel MR-guided attenuation correction procedures on hybrid PET-MR systems.

MRI-guided attenuation correction in whole-body PET/MR: assessment of the effect of bone attenuation.

OBJECTIVE: Hybrid PET/MRI presents many advantages in comparison with its counterpart PET/CT in terms of improved soft-tissue contrast, decrease in radiation exposure, and truly simultaneous and multi-parametric imaging capabilities. However, the lack of well-established methodology for MR-based attenuation correction is hampering further development and wider acceptance of this technology. We assess the impact of ignoring bone attenuation and using different tissue classes for generation of the attenuation map on the accuracy of attenuation correction of PET data. METHODS: This work was performed using simulation studies based on the XCAT phantom and clinical input data. For the latter, PET and CT images of patients were used as input for the analytic simulation model using realistic activity distributions where CT-based attenuation correction was utilized as reference for comparison. For both phantom and clinical studies, the reference attenuation map was classified into various numbers of tissue classes to produce three (air, soft tissue and lung), four (air, lungs, soft tissue and cortical bones) and five (air, lungs, soft tissue, cortical bones and spongeous bones) class attenuation maps. RESULTS: The phantom studies demonstrated that ignoring bone increases the relative error by up to 6.8% in the body and up to 31.0% for bony regions. Likewise, the simulated clinical studies showed that the mean relative error reached 15% for lesions located in the body and 30.7% for lesions located in bones, when neglecting bones. These results demonstrate an underestimation of about 30% of tracer uptake when neglecting bone, which in turn imposes substantial loss of quantitative accuracy for PET images produced by hybrid PET/MRI systems. CONCLUSION: Considering bones in the attenuation map will considerably improve the accuracy of MR-guided attenuation correction in hybrid PET/MR to enable quantitative PET imaging on hybrid PET/MR technologies.

A novel energy mapping approach for CT-based attenuation correction in PET.

PURPOSE: Dual-energy CT (DECT) is arguably the most accurate energy mapping technique in CT-based attenuation correction (CTAC) implemented on hybrid PET/CT systems. However, this approach is not attractive for clinical use owing to increased patient dose. The authors propose a novel energy mapping approach referred to as virtual DECT (VDECT) taking advantage of the DECT formulation but using CT data acquired at a single energy (kV(P)). For this purpose, the CT image acquired at one energy is used to generate the CT image at a second energy using calculated kV(P) conversion curves derived from phantom studies. METHODS: The attenuation map (µ-map) at 511 keV was generated for the XCAT phantom and clinical studies using the bilinear, DECT, and VDECT techniques. The generated µ-maps at 511 keV are compared to the reference derived from the XCAT phantom serving as ground truth. PET data generated from a predefined activity map for the XCAT phantom were then corrected for attenuation using µ-maps generated using the different energy mapping approaches. In addition, the generated µ-maps using the above described methods for a cylindrical polyethylene phantom containing different concentrations of K(2)HPO(4) in water were compared to actual attenuation coefficients. Likewise, CT images of five clinical whole-body studies were used to generate µ-maps using the various energy-mapping approaches were compared with µ-maps acquired at 511 keV using (68)Ge/(68)Ga rod sources for the clinical studies. RESULTS: The results of phantom studies demonstrate that the proposed method is more accurate than the bilinear technique. All three µ-maps yielded almost similar results for soft and lung tissues whereas for bone tissues, the DECT and the VDECT methods produced a much smaller mean relative difference (3.0% and 2.8%, respectively) than the bilinear approach (11.8%). Likewise, the comparison of PET images corrected for attenuation using the various methods showed that the proposed method provides better accuracy (6.5%) than the bilinear method (13.4%). Clinical studies further demonstrated that, compared to the bilinear method, the VDECT approach has better agreement for bony structures with the DECT technique (1.5% versus 8.9%) and transmission scanning (8.8% versus 17.7%). CONCLUSIONS: It was concluded that the proposed method outperforms the bilinear method especially in bony structures. Further evaluation using a large clinical PET/CT database is underway to evaluate the potential of the technique in a clinical setting.

3D calculation of absorbed dose for 131I-targeted radiotherapy: a Monte Carlo study.

Various methods, such as those developed by the Medical Internal Radiation Dosimetry (MIRD) Committee of the Society of Nuclear Medicine or employing dose point kernels, have been applied to the radiation dosimetry of (131)I radionuclide therapy. However, studies have not shown a strong relationship between tumour absorbed dose and its overall therapeutic response, probably due in part to inaccuracies in activity and dose estimation. In the current study, the GATE Monte Carlo computer code was used to facilitate voxel-level radiation dosimetry for organ activities measured in an (131)I-treated thyroid cancer patient. This approach allows incorporation of the size, shape and composition of organs (in the current study, in the Zubal anthropomorphic phantom) and intra-organ and intra-tumour inhomogeneities in the activity distributions. The total activities of the tumours and their heterogeneous distributions were measured from the SPECT images to calculate the dose maps. For investigating the effect of activity distribution on dose distribution, a hypothetical homogeneous distribution of the same total activity was considered in the tumours. It was observed that the tumour mean absorbed dose rates per unit cumulated activity were 0.65E-5 and 0.61E-5 mGY MBq(-1) s(-1) for the uniform and non-uniform distributions in the tumour, respectively, which do not differ considerably. However, the dose-volume histograms (DVH) show that the tumour non-uniform activity distribution decreases the absorbed dose to portions of the tumour volume. In such a case, it can be misleading to quote the mean or maximum absorbed dose, because overall response is likely limited by the tumour volume that receives low (i.e. non-cytocidal) doses. Three-dimensional radiation dosimetry, and calculation of tumour DVHs, may lead to the derivation of clinically reliable dose-response relationships and therefore may ultimately improve treatment planning as well as response assessment for radionuclide therapy.

Impact of miscentering on patient dose and image noise in x-ray CT imaging: phantom and clinical studies.

The operation of the bowtie filter in x-ray CT is correct if the object being scanned is properly centered in the scanner's field-of-view. Otherwise, the dose delivered to the patient and image noise will deviate from optimal setting. We investigate the effect of miscentering on image noise and surface dose on three commercial CT scanners. Six cylindrical phantoms with different size and material were scanned on each scanner. The phantoms were positioned at 0, 2, 4 and 6 cm below the isocenter of the scanner's field-of-view. Regression models of surface dose and noise were produced as a function of miscentering magnitude and phantom's size. 480 patients were assessed using the calculated regression models to estimate the influence of patient miscentering on image noise and patient surface dose in seven imaging centers. For the 64-slice CT scanner, the maximum increase of surface dose using the CTDI-32 phantom was 13.5%, 33.3% and 51.1% for miscenterings of 2, 4 and 6 cm, respectively. The analysis of patients' scout scans showed miscentering of 2.2 cm in average below the isocenter. An average increase of 23% and 7% was observed for patient dose and image noise, respectively. The maximum variation in patient miscentering derived from the comparison of imaging centers using the same scanner was 1.6 cm. Patient miscentering may substantially increase surface dose and image noise. Therefore, technologists are strongly encouraged to pay greater attention to patient centering.

Accurate Monte Carlo modeling and performance assessment of the X-PET subsystem of the FLEX triumph preclinical PET/CT scanner.

PURPOSE: X-PET is a commercial small animal PET scanner incorporating several innovative designs to achieve improved performance. It is employed as a PET subsystem in the FLEX Triumph preclinical PET/CT scanner, the first commercial small animal PET/CT scanner worldwide. The authors report on a novel Monte Carlo (MC) model designed for the evaluation of performance parameters of the X-PET METHODS: The Geant4 Application for Tomographic Emission (GATE) MC code was used as a simulation tool. The authors implemented more accurate modeling of the geometry of detector blocks and associated electronic chains, including dead-time and time-independent parameters, compared to previously presented MC models of the X-PET scanner. Validation of the MC model involved comparison between simulated and measured performance parameters of the X-PET, including spatial resolution, sensitivity, and noise equivalent count rate (NECR). Thereafter, various simulations were performed to assess scanner performance parameters according to NEMA NU 4-2008 standards with the aim to present a reliable Monte Carlo platform for small animal PET scanner design optimization. RESULTS: The average differences between simulated and measured results were 11.2%, 33.3%, and 9.1% for spatial resolution, sensitivity, and NECR, respectively. The average system absolute sensitivity was 2.7%. Furthermore, the peak true count rate, peak NECR, and scatter fraction were 2050 kcps, 1520 kcps, and 4.7%, respectively, for a mouse phantom and 1017 kcps, 469 kcps, and 18.2%, respectively, for a rat phantom. Spatial resolution was also measured in ten different positions at two axial locations. The radial, tangential, and axial FWHM ranged from 1.31 to 1.96 mm, 1.17 to 2.11 mm, and 1.77 to 2.44 mm, respectively, as the radial position varied from 0 to 25 mm at the centre of the axial field-of-view. CONCLUSIONS: The developed MC simulation platform provides a reliable tool for performance evaluation of small animal PET scanners and has the potential to be used in other applications such as detector design optimization, correction of image degrading factors such as randoms, scatter, intercrystal scatter, parallax error, and partial volume effect.

Measurement of scattered radiation in a volumetric 64-slice CT scanner using three experimental techniques.

Compton scatter poses a significant threat to volumetric x-ray computed tomography, bringing cupping and streak artefacts thus impacting qualitative and quantitative imaging procedures. To perform appropriate scatter compensation, it is necessary to estimate the magnitude and spatial distribution of x-ray scatter. The aim of this study is to compare three experimental methods for measurement of the scattered radiation profile in a 64-slice CT scanner. The explored techniques involve the use of collimator shadow, a single blocker (a lead bar that suppresses the primary radiation) and an array blocker. The latter was recently proposed and validated by our group. The collimator shadow technique was used as reference for comparison since it established itself as the most accurate experimental procedure available today. The mean relative error of measurements in all tube voltages was 3.9 +/- 5.5% (with a maximum value of 20%) for the single blocker method whereas it was 1.4 +/- 1.1% (with a maximum value of 5%) for the proposed blocker array method. The calculated scatter-to-primary ratio (SPR) using the blocker array method for the tube voltages of 140 kVp and 80 kVp was 0.148 and 1.034, respectively. For a larger polypropylene phantom, the maximum SPR achieved was 0.803 and 6.458 at 140 kVp and 80 kVp, respectively. Although the three compared methods present a reasonable accuracy for calculation of the scattered profile in the region corresponding to the object, the collimator shadow method is by far the most accurate empirical technique. Nevertheless, the blocker array method is relatively straightforward for scatter estimation providing minor additional radiation exposure to the patient.