Count Loss Research Articles

SU-F-BRCD-02: Activity Assay of a Y-90 Microsphere Sample Using a Coincidence Detection System.

This work takes advantage of a newly-determined, low-uncertainty branching ratio of the internal pair production component of Y-90 decay to spectroscopically assay the activity of a Y-90 microsphere sample with a coincidence detection system (CDS). The CDS pairs a HPGe detector with a large NaI detector. The system is able to electronically filter the bremsstrahlung continuum from the photon spectrum by gating the energy signal from the HPGe with the coincidence signal. This reduces the uncertainty in the spectra measurement compared to measurements with a single HPGe detector. A series of pulsers were used to correct for counting losses. A geometric characterization was completed to find the optimal source position for measurements. An efficiency calibration of the CDS was completed using a Na-22 standard source. To validate the measurement accuracy of the CDS, the activity of a Y-90 standard activity solution from the NIST SRM program was determined and compared to the value given by NIST. The CDS was then used to determine the activity of a Y-90 microsphere sample. This value was compared to the 3.0 GBq value given by the manufacturer. The activity determined with the CDS was within 2.6% from the given activity of the NIST SRM source, which is within the expanded uncertainty associated with the CDS measurement. The activity of the Y-90 microsphere sample was determined to be 3.72 GBq +/- 1.9%. This is 19% higher than the manufacturer-stated activity of 3 GBq. This is outside the manufacturer-stated uncertainty of +/-10%. The ability of CDS to determine the activity of a Y-90 source has been validated with comparison to a NIST Y-90 standard activity solution. The use of the CDS has been extended to determine the activity of a Y-90 microsphere sample.

Analytical and experimental evaluation of a counting method for particles added during the mask handling process

Extreme ultraviolet lithography has emerged as a highly promising next-generation lithography technique. However, some practical issues around mask technologies remain unresolved. Typically, the technique requires counting the particles released from or added to a mask blank (achieved using the knowledge of their position), a process referred to as an increase/decrease inspection. The counting process of this inspection has not been sufficiently studied because of the complexities of the counting error caused by counting losses and noise. However, the analysis of the counting process is essential to improve the counting accuracy. The author modeled the counting process by considering the difference between the actual occurrence of adhesion (or release) of the particles and the detection of their adhesion (or release) and verified the model experimentally. The author determined the necessary conditions for achieving the required accuracy by the multiple-inspection method, in which particles detected multiple times are identified as actual particles. The author found the counting errors in the increase/decrease inspection by the multiple-inspection method can be expressed as a function of the following: the numbers of unchanged, added, and released particles; the single-capture rate; and the number of inspections. Moreover, we found that the multiple-inspection method with four inspections is more accurate (pseudoparticles Np<10-4, counting error Nerr=0.065, standard deviation σ = 0.26) than the single-inspection approach (Np=10, Nerr=3.3, σ = 1.7). The author confirmed that the multiple-inspection method reliably determines whether particles were released or adhered using positional information.

Impact of Process Parameters on Listeria innocua Inactivation Kinetics by Pulsed Light Technology

The impact of several pulsed light (PL) processing parameters on microbial inactivation was evaluated in buffered water systems using Listeria innocua as test microorganism. Reduction in L. innocua population increased directly with pulse energy, pulse fluence and the number of light pulses, and inversely with the distance between samples and a xenon lamp. Overall, the higher the amount of light received by the target microorganism by both direct and reflected light, the larger the loss of cell counts. Total fluence striking on the samples per area unit was shown to be the most relevant process factor affecting L. innocua inactivation by PL. Microbial population decreased with total fluence, obtaining more than 7 log reductions after 0.4 J cm−2. The inactivation kinetics was clearly sigmoidal, showing an initial shoulder in the inactivation curve. No significant reduction (<1 log) in L. innocua counts was induced at fluences lower than 0.04 J cm−2. From this threshold total fluence, L. innocua inactivation increased exponentially to the maximum detectable level. Since total fluence is the most relevant process factor affecting microbial inactivation by PL, this parameter must be reported to describe PL processing conditions.

A preliminary investigation into a simple method for the determination of the mean ionisation energy of gas mixtures used in the NPL primary gas counting system

The activity concentration of gaseous beta-emitting radionuclides such as 3H, 85Kr and, more recently, 11C, is measured at NPL using a set of length-compensated proportional counters. The active gas is mixed with argon–methane (P-10) and passed to the counters. Adding gases to P-10 changes the mean ionisation energy, W, of the gas mixture. Estimation of the counting losses using the Monte Carlo model requires a knowledge of W. Unfortunately, only a limited amount of published data is available.This paper describes the initial experimental studies performed to enable the extension of the MC model based loss correction method to gases other than carbon dioxide in P-10. Preliminary measurements have been made to determine the W value for a gas mixture containing 85Kr in nitrogen and P-10. The DC current through the counters is measured; the counters are also operated in the normal way with pulse amplifiers, discriminators and scalers. The value of W is derived from a knowledge of activity, counter current and mean beta energy.

Least Among Equals

Least Among Equals

Development of Prognosis in Palliative care Study (PiPS) predictor models to improve prognostication in advanced cancer: prospective cohort study

ObjectiveTo develop a novel prognostic indicator for use in patients with advanced cancer that is significantly better than clinicians' estimates of survival.DesignProspective multicentre observational cohort study.Setting18 palliative care services in...

Periodontal status in HIV-positive individuals and its possible correlation with CD4+T cell count

Background : Infection with human immunodeficiency virus (HIV) results in loss of immunologic functions, especially those coordinated by CD4+ T-helper cells and consequent impairment of immune response. Periodontal disease has been associated with HIV infection, and HIV infection has been considered a modifier of periodontal disease. Aim: The aim of this study was to report the severity of periodontal disease in HIV-positive individuals and its association between clinical periodontal indices and CD4+T-cell count. Materials and Methods: 25 HIV-positive individuals were recruited and medical history was recorded. To evaluate periodontal disease, clinical attachment loss (CAL), oral hygiene index (OHI), and gingival bleeding index (GI) were recorded. Immune suppression was measured by peripheral blood CD4+T cells/mm 3 as analyzed by flow cytometry. Statistical Analysis: Association between CD4+ T levels and clinical parameters were determined using correlation coefficient test. Results: When all subjects were evaluated, a negative correlation was obtained between CD4+ T-cell count and clinical attachment loss ( r = -0.68226). In individuals with CD4+cell counts 3 , a negative correlation was obtained between clinical attachment loss (-0.35467) and GI (-0.35202). In patients with CD4 count Conclusion: Immune suppression in combination with risk factors may increase progression of periodontal disease. Hence, these individuals should practice better oral hygiene and regular follow-up.

COUNT RATE LIMITATIONS FOR PULSE-COUNTING INSTRUMENTATION IN PULSED ACCELERATOR FIELDS

This paper discusses various concepts involved in the counting losses of pulse-counting health physics instrumentation when used within the pulsed radiation environments of typical accelerator fields in order to preestablish appropriate limitations in use. Discussed are the "narrow" pulse and the "wide" pulse cases, the special effect of neutron moderating assemblies, and the effect of pulse fine microstructure on the counting losses of the pulse-counting instrumentation. In the narrow-pulse case, the accelerator pulse width is less than or equal to the instrument's dead time; whereas in the wide-pulse case, the accelerator pulse width is significantly longer than the instrument's dead time. Examples are provided that highlight the various concepts and limitations.

Reference measurement procedures for the accurate determination of cell concentrations: present status and future developments/Referenzmessverfahren für die genaue Bestimmung von Zellkonzentrationen: Status und zukünftige Entwicklungen

AbstractAccurate determination of cell concentrations serves as a valuable tool to support medical diagnosis and therapy control, e.g., in haematology, immunology and transfusion medicine. Intra- and inter-laboratory comparability of measurement results is essential for patient safety. To derive the so-called “conventional quantity value” of a measurand as target value for intra- or inter-laboratory quality assurance and to establish a traceability chain to the international System of Units (SI), a primary reference measurement procedure is needed, defined as a procedure which includes a complete analysis of influence quantities and perturbing factors and a complete description of measurement uncertainties. We describe a primary reference measurement procedure for the determination of erythrocyte concentration, based on flow cytometric cell counting by impedance measurements. To correct for instrument- and sample-dependent counting loss due to random coincidences, dilution series are prepared. The reference quantity value of the cell concentration is derived by extrapolation to vanishing volume fraction of the sample in the measurement suspension. Typically, for erythrocyte and leucocyte concentrations respective uncertainties of approximately 0.75% and 2% are reached. Future developments concern the extension of the procedures validated for erythrocyte and leucocyte counting by including immunological staining and microscopic techniques.

Performance Measurements of the Siemens mMR Integrated Whole-Body PET/MR Scanner

The recently released Biograph mMR is the first commercially available integrated whole-body PET/MR scanner. There are considerable advantages to integrating both modalities in a single scanner that enables truly simultaneous acquisition. However, there are also concerns about the possible degradation of both PET and MR performance in an integrated system. This paper evaluates the performance of the Biograph mMR during independent and simultaneous acquisition of PET and morphologic MR data. The NEMA NU 2-2007 protocol was followed for studying the PET performance. The following measurements were performed: spatial resolution; scatter fraction, count losses, and randoms; sensitivity; accuracy of the correction for count losses and randoms; and image quality. The quality control manual of the American College of Radiology was followed for studying the MR performance. The following measurements were performed: geometric accuracy, spatial resolution, low-contrast detectability, signal-to-noise ratio, static field (B(0)) homogeneity, radiofrequency field (B(1)) homogeneity, and radiofrequency noise. An average spatial resolution of 4.3 mm in full width at half maximum was measured at 1 cm offset from the center of the field of view. The system sensitivity was 15.0 kcps/MBq along the center of the scanner. The scatter fraction was 37.9%, and the peak noise-equivalent count rate was 184 kcps at 23.1 kBq/mL. The maximum absolute value of the relative count rate error due to dead-time losses and randoms was 5.5%. The average residual error in scatter and attenuation correction was 12.1%. All MR parameters were within the tolerances defined by the American College of Radiology. B(0) inhomogeneities below 1 ppm were measured in a 120-mm radius. B(1) homogeneity and signal-to-noise ratio were equivalent to those of a standard MR scanner. No radiofrequency interference was detected. These results compare favorably with other state-of-the-art PET/CT and PET/MR scanners, indicating that the integration of the PET detectors in the MR scanner and their operation within the magnetic field do not have a perceptible impact on the overall performance. The MR subsystem performs essentially like a standalone system. However, further work is necessary to evaluate the more advanced MR applications, such as functional imaging and spectroscopy.

Performance measurements of a depth-encoding TraPET detector module

The new method to correct a parallax error and the loss of coincidence counts caused by the gap between modules was developed for a small animal PET scanner. We proposed the TraPET scanner composed of 6 dual-layer phoswich detector modules. Each detector module consists of a 5.0 mm-thick trapezoidal-shaped monolithic LSO crystal and a 23 x 23 array of GSO crystal. The layer of interaction is identified by the pulse shape discrimination method. One detector module was built and the algorithm for layer identification was optimized. The dual-layer crystals were optically coupled to a Hamamatsu H8500 position-sensitive PMT and a resistive charge divider was used to multiplex 64-channel anode outputs into 4-channel position signals. The 4 signals have been sampled continuously by 14-bit ADC at a sampling rate of 105 MHz and the pulse shape discrimination algorithm was achieved through FPGA programming. The detector module was irradiated with a Na-22 point source from the side of the crystals to obtain flood images of each layer and two layers were clearly identified, thus verifying the DOI capability. The TraPET detector proved to be a reliable design for correcting the parallax error and improving the sensitivity simultaneously in the small animal PET.

FlowCAM: Sizing cells and understanding the impact of size distributions on biovolume of ­planktonic community structure

Instruments for in vivo identification and quantification of marine organisms are becoming more common, and the interpretation of data from these instruments is still evolving. In the present study, we compare the sizing performance of 3 instruments: (1) a black and white (B/W) FlowCAM II; (2) a BeckmanCoulter Multisizer III (MIII); and (3) an inverted microscope. We applied 3 different particle sizing algorithms available from the FlowCAM to suspensions of 5 dif- ferent particle morphotypes (4 different phytoplankton species and a spherical NIST calibration bead). The FlowCAM generated size distributions similar to those reported by the MIII for the spherical calibration beads. However, differences in reported sizes emerged among FlowCAM algorithms as well as among instruments when applied to morphologically more complex parti- cles, such as diatom chains. There was an immediate and substantial loss of cell counts when live cells were fixed in Lugol's solution, but only minor differences in cell size distributions among the different FlowCAM algorithms. The difference in sizing performance of the FlowCAM algorithms affects biovolume estimates of the natural plankton samples analysed. Species diversity was apparently higher in samples analysed by microscopy than with the FlowCAM, but the cell size distribution from the microscope was extremely narrow compared to FlowCAM and MIII. The present study demonstrates that the particle sizing algorithm has severe impact on the character- istics of the particle size distribution and on the total community biomass estimate.

Development of Prognosis in Palliative care Study (PiPS) predictor models to improve prognostication in advanced cancer: prospective cohort study

Objective To develop a novel prognostic indicator for use in patients with advanced cancer that is significantly better than clinicians’ estimates of survival.Design Prospective multicentre observational cohort study.Setting 18 palliative...

Clinical and nutritional status of surgical patients with and without malignant diseases: cross-sectional study

Malnutrition is frequently observed in inpatients with malignant diseases and may contribute to longer hospital stays. To compare the nutritional status, lymphocyte count, hemoglobin values and length of hospital stay of patients with and without malignant diseases. This comparative study assessed indicators of nutritional status, namely body mass index, recent weight loss, lymphocyte count, hemoglobin and length of hospital stay, of 928 surgical patients with and without malignant diseases (50.2% females and 49.8% males). The chi-square test was used to compare proportions and the Mann-Whitney test was used to compare continuous measurements between two groups. The significance level was set at 5%. Patients with malignant diseases had longer hospital stays (P<0.0001), furthermore, a higher percentage of patients with malignant diseases had body mass index <18.5 (P<0.0001) and experienced recent weight changes (P<0.0002). Lymphocyte count also differed statistically between the groups (P = 0.0131), which lower levels were identified among patients with malignant diseases. The lymphocyte count, hemoglobin values and weight loss are important findings of nutritional depletion in patients with malignant diseases.

Development of a Current-Readout Type Neutron Monitor for Burst Neutron Fields

*We report on the development of a current-readout type neutron monitor for the measurement of the dose rate of burst neutrons generated by beam loss in an accelerator that occurs within a short time span. This neutron monitor consists of a commercially available neutron proportional counter, a 6.5-cm thick polyethylene moderator, and a newly developed charge-integration circuit. The monitor was tested under mono-energetic neutron standard fields (En = 8 keV to 15 MeV) and was compared with a conventional pulse-readout type monitor. The energy response of the current-readout monitor is identical to that of the pulse-readout monitor. The current-readout monitor is able to measure neutron doses up to 4.5 mSv/h without count loss, whereas the pulse-readout monitor fails due to count loss.

Determination of proper peaking time for Ultra-LEGe detector

Reducing count losses and pile-up pulse effects in quantitative and qualitative analysis is necessary for accuracy of analysis. Therefore, the proper peaking time for particular detector systems is important. The characteristic X-rays emitted from pure some elements were detected by using an Ultra-LEGe detector connecting a Tennelec TC 244 spectroscopy amplifier at different peaking time modes. Overall pulse widths were determined by an HM 203-7 oscilloscope connecting amplifier. The proper peaking time for Ultra-LEGe is determined as 3.84 μs.

Modeling the performance of a photon counting x‐ray detector for CT: Energy response and pulse pileup effects

Recently, photon counting x-ray detectors (PCXDs) with energy discrimination capabilities have been developed for potential use in clinical computed tomography (CT) scanners. These PCXDs have great potential to improve the quality of CT images due to the absence of electronic noise and weights applied to the counts and the additional spectral information. With high count rates encountered in clinical CT, however, coincident photons are recorded as one event with a higher or lower energy due to the finite speed of the PCXD. This phenomenon is called a "pulse pileup event" and results in both a loss of counts (called "deadtime losses") and distortion of the recorded energy spectrum. Even though the performance of PCXDs is being improved, it is essential to develop algorithmic methods based on accurate models of the properties of detectors to compensate for these effects. To date, only one PCXD (model DXMCT-1, DxRay, Inc., Northridge, CA) has been used for clinical CT studies. The aim of that study was to evaluate the agreement between data measured by DXMCT-1 and those predicted by analytical models for the energy response, the deadtime losses, and the distorted recorded spectrum caused by pulse pileup effects. An energy calibration was performed using 99mTc (140 keV), 57Co (122 keV), and an x-ray beam obtained with four x-ray tube voltages (35, 50, 65, and 80 kVp). The DXMCT-1 was placed 150 mm from the x-ray focal spot; the count rates and the spectra were recorded at various tube current values from 10 to 500 microA for a tube voltage of 80 kVp. Using these measurements, for each pulse height comparator we estimated three parameters describing the photon energy-pulse height curve, the detector deadtime tau, a coefficient k that relates the x-ray tube current I to an incident count rate a by a = k x I, and the incident spectrum. The mean pulse shape of all comparators was acquired in a separate study and was used in the model to estimate the distorted recorded spectrum. The agreement between data measured by the DXMCT-1 and those predicted by the models was quantified by the coefficient of variation (COV), i.e., the root mean square difference divided by the mean of the measurement. Photon energy versus pulse height curves calculated with an analytical model and those measured using the DXMCT-1 were in agreement within 0.2% in terms of the COV. The COV between the output count rates measured and those predicted by analytical models was 2.5% for deadtime losses of up to 60%. The COVs between spectra measured and those predicted by the detector model were within 3.7%-7.2% with deadtime losses of 19%-46%. It has been demonstrated that the performance of the DXMCT-1 agreed exceptionally well with the analytical models regarding the energy response, the count rate, and the recorded spectrum with pulse pileup effects. These models will be useful in developing methods to compensate for these effects in PCXD-based clinical CT systems.

NEMA NU 4-2008 Performance Measurements of Two Commercial Small-Animal PET Scanners: ClearPET and rPET-1

In this work, we compare two commercial positron emission tomography (PET) scanners installed at CIEMAT (Madrid, Spain): the ClearPET and the rPET-1. These systems have significant geometrical differences, such as the axial field of view (110 mm on ClearPET versus 45.6 mm on rPET-1), the configuration of the detectors (whole ring on ClearPET versus one pair of planar blocks on rPET-1) and the use of an axial shift between ClearPET detector modules. We used an assessment procedure that fulfilled the recommendations of the National Electrical Manufacturers Association (NEMA) NU 4-2008 standard. The methodology includes studies of spatial resolution, sensitivity, scatter fraction, count losses and image quality. Our experiments showed a central spatial resolution of 1.5 mm (transaxial), 3.2 mm (axial) for the ClearPET and 1.5 mm (transaxial), 1.6 mm (axial) for the rPET-1, with a small variation across the transverse axis on both scanners (~1 mm). The absolute sensitivity at the centre of the field of view was 4.7% for the ClearPET and 1.0% for the rPET-1. The peak noise equivalent counting rate for the mouse-sized phantom was 73.4 kcps reached at 0.51 MBq/mL on the ClearPET and 29.2 kcps at 1.35 MBq/mL on the rPET-1. The recovery coefficients measured using the image quality phantom ranged from 0.11 to 0.89 on the ClearPET and from 0.14 to 0.81 on the rPET-1. The overall performance shows that both the ClearPET and the rPET-1 systems are very suitable for preclinical research and imaging of small animals.

The correlation between hygienic parameters of milk and weight loss of semihard cheese

The purpose of the paper was to examine weight loss and correlation between total bacteria count and the somatic cells count and weight loss of semihard naturally dried cheese, product of dairy plant ZZ?Cijevna? in Podgorica. Weigt loss was calculated on the base of difference in mass of cheese at the beginning of ripening and after specified period of ripening, exposed in percents. Examination of weight loss was done on total six product series of cheese during 60 days of ripening on temperature 14,20C and RH of 89%. Obtained average values for weight loss of cheese were: after 10 days 4.723%, 20 days 8.789% and after 30 days of ripening 11.020%. Weight loss of cheese in period of ripening 10-20 days was 4.266%, in period 20-30 days 2,445% and in period of ripening 30-60 days 5.507%. The total bacteria count in milk was determined on apparatus BactoScan FC 100 and the somatic cells count on apparatus Fossomatic 5000. The middle positive correlation between somatic cells count in milk and weight loss of cheese in period 1-10 days of ripening (0.69156), as well as middle positive correlation (0.767336) between total bacteria count and weight loss of cheese 1-10 days of ripening were determined. The obtained results show that weight loss of cheese was highest in period 1-10 days of ripening and that there is significant influence of hygienic quality of milk on weight loss of cheese and economy of production.

Quantitative 177 Lu SPECT (QSPECT) imaging using a commercially available SPECT/CT system

Purpose: The combination of single photon emission computed tomography (SPECT) and computer tomography (CT) that incorporates iterative reconstruction algorithms with attenuation and scatter correction should facilitate accurate non-invasive quantitative imaging. Quantitative SPECT (QSPECT) may improve diagnostic ability and could be useful for many applications including dosimetry assessment. Using 177Lu, we developed a QSPECT method using a commercially available SPECT/CT system. Methods: Serial SPECT of 177Lu sources (89–12,400 MBq) were acquired with multiple contiguous energy windows along with a co-registered CT, and were reconstructed using an iterative algorithm with attenuation and scatter correction. Camera sensitivity (based on reconstructed SPECT count rate) and dead-time (based on wide-energy spectrum count rate) were resolved by non-linear curve fit. Utilizing these parameters, a SPECT dataset can be converted to a QSPECT dataset allowing quantitation in Becquerels per cubic centimetre or standardized uptake value (SUV). Validation QSPECT/CT studies were performed on a 177Lu cylindrical phantom (7 studies) and on 5 patients (6 studies) who were administered a therapeutic dose of [177Lu]octreotate. Results: The QSPECT sensitivity was 1.08 × 10−5 ± 0.02 × 10−5 s−1 Bq−1. The paralyzing dead-time constant was 0.78 ± 0.03 µs. The measured total activity with QSPECT deviated from the calibrated activity by 5.6 ± 1.9% and 2.6 ± 1.8%, respectively, in phantom and patients. Dead-time count loss up to 11.7% was observed in patient studies. Conclusion: QSPECT has high accuracy both in our phantom model and in clinical practice following [177Lu]octreotate therapy. This has the potential to yield more accurate dosimetry estimates than planar imaging and facilitate therapeutic response assessment. Validating this method with other radionuclides could open the way for many other research and clinical applications.