Graphene-based nanocomposites as gamma- and X-ray radiation shield.

Commonly used materials for protection against ionizing radiation (gamma and X-ray energy range) primarily rely on high-density materials, like lead, steel, or tungsten. However, these materials are heavy and often impractical for various applications, especially where weight is a key parameter, like in avionics or space technology. Here, we study the shielding properties of an alternative light material-a graphene-based composite with a relatively low density ~ 1 g/cm3. We demonstrate that the linear attenuation coefficient is energy of radiation dependent, and it is validated by the XCOM model, showing relatively good agreement. We also show that the mass attenuation coefficient for selected radiation energies is at least comparable with other known materials, exceeding the value of 0.2 cm2/g for higher energies. This study proves the usefulness of a commonly used model for predicting the attenuation of gamma and X-ray radiation for new materials. It shows a new potential candidate for shielding application.

Assessment of Renal Function Based on Dynamic Scintigraphy Parameters in the Diagnosis of Obstructive Uro/Nephropathy.

This study evaluates the usefulness of parameters allowing assessment of renal function in absolute values in dynamic renal scintigraphy (DRS) with 99mTc-ethylenedicysteine (99mTc-EC) uptake constant (K), mean transit time (MTT), and parenchymal transit time (PTT) in the diagnosis of obstructive uro/nephropathy. The study included 226 people: 20 healthy volunteers, for whom normative values of assessed parameters were determined, and 206 patients. Reproducibility of results obtained by two independent operators, specificity, correlation with estimated GFR (eGFR), and Cohen's kappa were used to evaluate reliability of assessed parameters. Normative values were as follows: K ≥ 1.6, MTT ≤ 250 s, and PTT ≤ 225 s. Reproducibility of determination of K (rs = 0.99) and MTT (rs = 0.98) was significantly higher than that of PTT (rs = 0.95) (p = 0.001). Specificity was 100% for K, 81% for MTT, and 91% for PTT. Correlation of eGFR with K (rs = 0.89) was significantly higher than with PTT (rs = 0.53) and with split function (SF) (rs = 0.66) (p < 0.0001). Cohen's kappa was κ = 0.89 for K, κ = 0.88 for MTT, and κ = 0.77 for PTT. In a group of patients where standard DRS parameters are unreliable (bilateral obstructive uro/nephropathy or single functioning kidney), the use of K (the most effective among assessed parameters) changed the classification of 23/79 kidneys (29%). K enables reproducible assessment of absolute, individual kidney function without modifying routine DRS protocol. Diagnostic value of MTT and PTT is limited.

Inter- and Intraobserver Repeatability of Myocardial Flow Reserve Values Determined with SPECT Study Using a Discovery NM530c Camera and Corridor 4DM Software.

BACKGROUND: Myocardial blood flow (MBF) and flow reserve (MFR) examination, especially useful in the diagnosis of multivessel coronary artery disease (CAD), can be assessed with a cadmium-zinc-telluride (CZT) SPECT gamma camera, as an alternative to the expensive and less available PET. However, study processing is not free from subjective factors. Therefore, this paper aims to evaluate intra- and interobserver repeatability of MBF and MFR values obtained by the same operator and two independent operators. METHODS: This study included 57 adult patients. MBF and MFR were assessed using a Discovery NM530c camera in a two-day, rest/dipyridamople protocol, using 99mTc-MIBI. Data were processed using Corridor4DM software, twice by one operator and once by another operator. RESULTS: The repeatability of the assessed values was quite good in the whole myocardium, LAD and LCX vascular territories, but was poor in the RCA territory. CONCLUSIONS: The poor repeatability of MBF and MFR in RCA vascular territory can be explained by poor automatic orientation of the heart axis during post-processing and a so-called "cardiac creep" phenomenon. Better automatic heart orientation and introduction of automatic motion correction is likely to drastically improve this repeatability. In the present state of the software, PET is better for patients requiring assessment of MFR in the RCA territory.

Kidney efficiency index quantitative parameter of a dynamic renal scintigraphy. II. usefulness in the diagnosis of obstructive nephropathy.

BACKGROUND: One of the main indications for DRS is a diagnosis of obstructive uro-/nephropathy. In standard practice, this study includes the assessment of sequential scintigraphic images, renographic curves and such quantitative parameters as TMAX, T1/2 and split function of each kidney (SF). Due to the relative nature of SF and limitations of diagnostic capabilities of TMAX and T1/2, DRS was expanded to include new quantitative parameters describing kidney function in absolute values. This study aims to evaluate the usefulness of kidney efficiency index (KEi) - new, in-house developed parameter proportional to the average clearance function of the kidney. MATERIAL AND METHODS: The study included 156 people aged 18-84 (average 51) years. The first group, from which normative values of new parameters were determined, consisted of 20 healthy volunteers. The second group consisted of 136 patients selected retrospectively, based on archived scintigraphic data. "Normalcy rate" (percentage of normal results among selected 62 patients with a low likelihood of obstructive uro-/nephropathy) was used to evaluate the reliability of KEi. A comparative differential analysis of obstructive uro-/nephropathy, based on standard and new DRS parameters, was performed on selected 74 patients (92 kidneys) with single functioning kidney or bilateral obstructive uropathy, where SF is unreliable. RESULTS: Normative values: KEi ≥ 8; Normalcy rate for KEi: 95%. In comparison with standard DRS evaluation, application of KEi changed the diagnosis in 1/3 of assessed kidneys (from uropathy to nephropathy in 27/92 kidneys and vice versa in 4 kidneys). CONCLUSIONS: KEi enables reproducible, quantitative assessment of absolute kidney function without any modifications of the standard DRS protocol. Its values can be compared between independent studies (e.g. follow-up examinations). KEi corrected the diagnosis of obstructive uro-/nephropathy in cases of single functioning kidney or bilateral obstructive uropathy.

Kidney Efficiency Index - quantitative parameter of a dynamic renal scintigraphy. I. Theory and preliminary verification.

BACKGROUND: One of the basic clinical indications for dynamic renal scintigraphy (DRS) is a diagnosis of obstructive uropathy and/or nephropathy. Currently, a basic quantitative criterion for diagnosing nephropathy is the percentage of individual kidney's contribution in the global uptake of a radiopharmaceutical from the blood (so-called Split Function - SF). From a clinical point of view, a parameter evaluating a radiopharmaceutical uptake and reflecting the efficiency of a specific kidney, determined independently of the total uptake of both kidneys, would be much more useful. Based on a Rutland theory, a kidney uptake constant K proportional to a radiotracer uptake by individual kidney was introduced and applied to DRS with 99mTc-ethylene-1-dicysteine (99mTc-EC). In addition, a kidney efficiency index (KEi) was also worked out as a new parameter obtained by dividing the uptake constant K by the surface of the ROI of a given kidney, which can be interpreted as the average "efficiency" of clearance of a kidney. MATERIAL AND METHODS: K and KEi values were verified in 72 studies selected retrospectively from patients referred routinely for DRS, with available current level of blood creatinine, used for calculation of estimated GFR (eGFR) according to a CKD-EPI formula. After splitting of eGFR values into individual kidneys according to SF, single kidney eGFR values (SKeGFR) were obtained and then used as a verification method for SF, K and KEi values. RESULTS: Correlation between SF and SKeGFR values, rsp = 0.64, was significantly weaker (p < 0.0022) than the correlation of SKeGFR values with K uptake constants and KEi indices: 0.90 and 0.84, respectively. CONCLUSIONS: Uptake constant K and KEi, as quantitative parameters, give the opportunity to analyze a function of each kidney separately and in an absolute way. KEi also allows for a reliable assessment of kidneys of atypical sizes (larger or smaller than average). It also gives the opportunity to create normative values for this parameter and may be useful in a number of clinical situations where the diagnostic effectiveness of such a relative parameter as SF, is severely limited, e.g. in assessing a large kidney with hydronephrosis or while differing a cirrhotic from hypoplastic (i.e. a small but properly functioning) kidney.

Application of stress-only myocardial perfusion imaging.

BACKGROUND: Single-photon emission computed tomography myocardial perfusion study is usually a sequence of stress and rest part. In case of a normal stress study rest part can be given up. The objective of this study was to examine factors affecting concordance of results of stress-only (SO) and stress-rest (SR) studies. MATERIAL AND METHODS: SO and SR studies without and with attenuation correction (AC) of 212 selected patients (without cardiomyopathy, history of myocardial infarction or coronary artery bypass grafting) were analyzed visually. Influence of percutaneous coronary intervention (PCI) in the past, type of stress (physical/pharmacological) and application of AC (in form of combined method of non-corrected and corrected images - CM), patient body mass index (BMI) and gender on concordance rates of SO and SR studies were examined. RESULTS: Neither a history of PCI, nor a type of stress affected concordance rate. AC (in form of CM) improved concordance rate significantly, from 60% to 68% (p = 0.018). Patient BMI affected concordance rates - 72% in non-obese and 59% in obese patients (p = 0.05). In the whole group, risk of overlooking patients with abnormal perfusion in SO study was small (< 2%), but it grew significantly with patient BMI. Rest study was necessary in about 20% of non-obese and in about 50% of obese patients. CONCLUSION: MPS can be limited to stress part in appropriately selected, especially non-obese, patients provided that AC is applied, due to a low risk of overlooking patients with abnormal perfusion. In case of obese patients, careful analysis of exercise images for their normality is particularly important.

Application of normalized values of kidney clearance function in the diagnosis of bilateral obstructive nephropathy - a preliminary report.

BACKGROUND: Dynamic renal scintigraphy provides effective diagnosis of obstructive uropathy and nephropathy. However, in case of a bilateral outflow impairment, relative differential renal function (DRF), which is a primary quantitative criterion for diagnosis of unilateral obstructive nephropathy (when its value is below 45%, according to EANM guidelines from 2011), becomes unreliable. In case of bilateral nephropathy with similar severity, this parameter may even be within the normal range (45-55%) for both kidneys. The aim of this study was therefore to assess diagnostic usefulness of the original, normalized, absolute parameter proportional to the value of renal clearance function (K) in the evaluation of obstructive nephropathy in a group of patients with bilateral uropathy. MATERIAL AND METHODS: 16 healthy volunteers (32 kidneys) without history of kidney diseases were examined to determine normative value of K index. Then, 8 patients (16 kidneys) with bilateral obstructive uropathy found in standard dynamic renal scintigraphy performed using 111 MBq of 99mTc-EC (cumulative renographic curve that continued rising or dropped by less than 50% after i.v. administration of Furosemide) were examined. For each of the subjects 60 sequential 20s images were obtained, which were then assessed using an original method of post-processing scintigraphic data. It included normalization of renographic curves to the area under the heart curve. Subsequently, these normalized values from the uptake phase (between 2nd and 3rd minute) were inserted into the linear regression equation, from which K index was obtained. RESULTS: In healthy volunteers the average value of K index was 0.23 ± 0.05. The value of 0.13 (mean -2 SD) was taken as the lower limit of the norm. Values below that limit suggest obstructive nephropathy. In patients with bilateral obstructive uropathy, 5 kidneys met the conventional criteria of nephropathy (DRF < 45%), while 11 kidneys had DRF within normal range. K index was below the norm in 9 kidneys (including 4 kidneys with low and 5 with normal DRF), while its value was normal in 7, including one kidney with reduced DRF (37%). K index changed the diagnosis in 6 kidneys out of 16 (38%). CONCLUSIONS: Preliminary results indicate usefulness of K index in diagnosis of obstructive nephropathy in patients with bilateral obstructive uropathy. For further evaluation of clinical value of this method, it is planned to examine a larger group of patients with varying degrees of renal parenchymal function impairments.

Reduced-time myocardial perfusion study processed with "Myovation Evolution" - assessment of diagnostic efficacy.

BACKGROUND: While assessing images using standard segmental method, we felt that some defects were either underscored or missed. So this work is intended to compare results of low count myocardial perfusion studies (MPS) processed with "Myovation Evolution", applying complete evaluation of all available slices, with full count studies and assess impact of reduction of counts on diagnostic efficacy of the study. MATERIAL AND METHODS: A retrospective study was conducted in a group of 95 patients (56 males, age 62 ± 9 years, BMI 28 ± 4) with known or suspected CAD, without clinical history or any signs of a previous myocardial infarction. All patients underwent coronary angiography (CA) within 3 months of MPS. CA was used as a reference method for diagnostic performance of MPS. Patients underwent a stress/rest 2-day MPS. Both studies were performed twice, with normal (25 s) and shortened (13 s) time/projection. Studies were processed using Myovation protocol (OSEM, 2 iterations, 10 subsets) for full time (FT) studies and a Myovation Evolution protocol for half time (HT) studies (OSEM, 12 iterations, 10 subsets, Resolution Recovery). Reconstructed images, with and without attenuation correction (AC), were evaluated by 2 experienced nuclear medicine specialists (a consensus) visually, taking into account all available slices, in a 5-grade scale (normal, probably normal, equivocal, probably abnormal and abnormal). Study results were additionally dichotomized as normal or abnormal. Perfusion defects were assigned to coronary arteries. RESULTS: An exact agreement between FT and HT study assessment, without AC, amounted to 66%, with AC it grew to 79%, p = 0.05. In studies without AC 10 perfusion defects were found only in HT studies in RCA area in male patients. A higher percentage of studies with perfusion defects in RCA area visible only in HT studies was found among discordant (7/25, 28%) than concordant results (3/70, 4%), p = 0.003. AC reduced this difference. HT study provided lower accuracy in detection of CAD than FT study (58% vs. 68%, p = 0.034). AC reduced this difference considerably. Dichotomized assessment agreed in 81% of studies without AC and in 87% with AC. CONCLUSIONS: Myovation Evolution protocol requires application of AC otherwise perfusion defects in RCA area in male patients are falsely detected. Shortened studies reconstructed with "Myovation Evolution" package without AC reveal a tendency toward reduction of accuracy of the study in detection of CAD. AC makes up for this reduction.

Diagnostic value of optimised real-time sonoelastography in the assessment of liver fibrosis in chronic hepatitis B and C.

AIM: To optimise the method of real-time elastography (RTE) in the assessment of liver fibrosis using an in-house prepared method for elastogram analysis, as well as a semiquantitative analysis based on newly introduced parameters. MATERIAL AND METHODS: Sonoelastography was performed in 94 patients with various degrees of liver fibrosis and also in 25 healthy volunteers. As a reference method for diagnostic efficacy of sonoelastography-based parameters used for the assessment of fibrosis degree in patients with chronic B and C hepatitis, a liver biopsy was used. Patient's elastograms were analysed using in-house prepared software, Pixel Count, calculating two semiquantitative parameters: mean stiffness fraction (MSF%) and intrinsic stiffness ratio (ISR). RESULTS: Statistically significant differences between distributions of the above presented parameters for different degrees of liver fibrosis were revealed. Indices of diagnostic efficacy for detection of significant liver fibrosis (F ≥ 2) using MSF% amounted to: sensitivity - 76%, specificity - 87% and ISR: 81% and 87%, respectively. Sensitivity of both parameters in detection of cirrhosis (F = 4) was equal to 88% and specificity amounted to: for MSF% - 84% and ISR - 86%. Interobserver reproducibility determined for both of the above parameters was high, intraclass correlation coefficients (ICC) were 0.91 for MSF% and 0.93 for ISR. CONCLUSIONS: Real-time elastography applied in this study, using in-house prepared Pixel Count software, provided good reproducibility and diagnostic efficacy, especially specificity, in the assessment of liver fibrosis degree.

Comparison of shortened gated myocardial perfusion imaging processed with "Myovation Evolution" with full time study.

BACKGROUND: The work compares the results of shortened gated myocardial perfusion imaging (MPI), processed with "Myovation Evolution" software, with a study performed in a standard way. MATERIAL AND METHODS: A retrospective study was conducted in a group of 95 patients (56 males and 39 females, age 62 ± 9 years, BMI 28 ± 4) with known or suspected CAD, without clinical history or any signs of a previous myocardial infarction. All patients underwent coronary angiography (CA) within 3 months of MPI. CA was used as a reference for diagnostic performance of MPI. Patients underwent a stress/rest 2-day MPI. Both studies were performed twice, with normal (25s) and shortened (13s) time per projection. Studies were processed using Myovation protocol (OSEM with 2 iterations and 10 subsets) for full time (FT) studies and a Myovation Evolution protocol dedicated to half time (HT) studies (OSEM with 12 iterations, 10 subsets). Reconstructed images, with and without attenuation correction (AC), were evaluated by 2 experienced nuclear medicine specialists (a consensus), with regard to image quality and perfusion, evaluated using a visual semi-quantitative method, applying a standard division of myocardium into 17 segments. Perfusion was assessed in every segment using a standard 5 grade scale. Summed stress scores were calculated for every patient and threshold values for detection of CAD were selected based on ROC analysis with CA treated as a reference method. After 2 months FT images were interpreted again by the same specialists. RESULTS: The quality of images obtained from shortened and normal studies was equally good. All correlation coefficients between segmental scorings of FT and HT studies were high and statistically significant. Correlation coefficients between corresponding segments in FTAC and HTAC (i.e. with AC) studies were systematically higher than without AC. The agreement between FT and HT study results was equal to 81% for FT and HT studies and to 86% for FTAC and HTAC studies (p = 0.40). The repeatability of FTAC study assessments was equal to 94%. 95-percent confidence intervals calculated for agreement between FTAC and HTAC studies and the repeatability of FTAC study overlapped considerably. Correlation coefficients for EDV, ESV and EF values between FT and HT were high: 0.93, 0.96 and 0.88, respectively. CONCLUSION: Myovation Evolution protocol used for reconstruction of myocardial perfusion studies with reduced number of counts requires AC. The agreement between the results of visual assessment of normal and reduced count studies is high and not worse than the agreement between repeat assessment of a full time study.