Quantitative SPECT (QSPECT) at high count rates with contemporary SPECT/CT systems

Abstract Background Accurate QSPECT is crucial in dosimetry-based, personalized radiopharmaceutical therapy with 177Lu and other radionuclides. We compared the quantitative performance of three NaI(Tl)-crystal SPECT/CT systems equipped with low-energy high-resolution collimators from two vendors (Siemens Symbia T6; GE Discovery 670 and NM/CT 870 DR). Methods Using up to 14 GBq of 99mTc in planar mode, we determined the calibration factor and dead-time constant under the assumption that these systems have a paralyzable behaviour. We monitored their response when one or both detectors were activated. QSPECT capability was validated by SPECT/CT imaging of a customized NEMA phantom containing up to 17 GBq of 99mTc. Acquisitions were reconstructed with a third-party ordered subset expectation maximization algorithm. Results The Siemens system had a higher calibration factor (100.0 cps/MBq) and a lower dead-time constant (0.49 μs) than those from GE (75.4–87.5 cps/MBq; 1.74 μs). Activities of up to 3.3 vs. 2.3–2.7 GBq, respectively, were quantifiable by QSPECT before the observed count rate plateaued or decreased. When used in single-detector mode, the QSPECT capability of the former system increased to 5.1 GBq, whereas that of the latter two systems remained independent of the detectors activation mode. Conclusion Despite similar hardware, SPECT/CT systems’ response can significantly differ at high count rate, which impacts their QSPECT capability in a post-therapeutic setting.

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Design of MIRA, a low-noise pixelated ASIC for the readout of micro-channel plates

Journal of Instrumentation ◽

10.1088/1748-0221/17/01/c01047 ◽

2022 ◽

Vol 17 (01) ◽

pp. C01047

Author(s):

E. Fabbrica ◽

M. Carminati ◽

D. Butta ◽

M. Uslenghi ◽

M. Fiorini ◽

...

Keyword(s):

Spatial Resolution ◽

Count Rate ◽

Dynamic Range ◽

Dead Time ◽

Uv Spectroscopy ◽

Low Noise ◽

Micro Channel ◽

High Count ◽

Processing Times ◽

Channel Plate

Abstract We present the design of the first prototype of MIRA (MIcro-channel plate Readout ASIC) that has been designed to read out Micro-Channel Plates (MCP), in particular for UV spectroscopy. MIRA will be able to detect the cloud of electrons generated by each photon interacting with the MCP, sustaining high local and global count rates to fully exploit the MCP intrinsic dynamic range with low dead time. The main rationale that guided the electronics design is the reduction of the input Equivalent Noise Charge (ENC) in order to allow operations with lower MCP gain, thus improving its lifetime, crucial aspect for long missions in space. MIRA features two selectable analog processing times, 133 ns or 280 ns (i.e. fast mode or slow mode), granting a count rate per pixel of 100 kcps. Moreover, it shows an Equivalent Noise Charge ENC = 17 e r m s − . A spatial resolution of 35 μm and an operation with zero dead time, due to the readout, are targeted. The low noise, high count rate and high spatial resolution requirements are expected by keeping a compact pixel size (35 μm × 35 μm) for a total of 32 × 32 pixels in a 2 mm × 2 mm ASIC area. In this work, the ASIC design is described.

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Gamma camera characterization at high holmium-166 activity in liver radioembolization

EJNMMI Physics ◽

10.1186/s40658-021-00372-9 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Martina Stella ◽

Arthur J. A. T. Braat ◽

Marnix G. E. H. Lam ◽

Hugo W. A. M. de Jong ◽

Rob van Rooij

Keyword(s):

Image Quality ◽

Count Rate ◽

Gamma Camera ◽

Activity Concentration ◽

Dead Time ◽

Scatter Correction ◽

High Count ◽

Scanning Time ◽

Medicine Physician ◽

Lung Shunt

Abstract Background High activities of holmium-166 (166Ho)–labeled microspheres are used for therapeutic radioembolization, ideally directly followed by SPECT imaging for dosimetry purposes. The resulting high-count rate potentially impacts dead time, affecting the image quality and dosimetric accuracy. This study assesses gamma camera performance and SPECT image quality at high 166Ho activities of several GBq. To this purpose, the liver compartment, including two tumors, of an anthropomorphic phantom was filled with 166Ho-chloride, with a tumor to non-tumorous liver activity concentration ratio of 10:1. Multiple SPECT/CT scans were acquired over a range of activities up to 2.7 GBq. Images were reconstructed using a commercially available protocol incorporating attenuation and scatter correction. Dead time effects were assessed from the observed count rate in the photopeak (81 keV, 15% width) and upper scatter (118 keV, 12% width) window. Post reconstruction, each image was scaled with an individual conversion factor to match the known total activity in the phantom at scanning time. The resulting activity concentration was measured in the tumors and non-tumorous liver. The image quality as a function of activity was assessed by a visual check of the absence of artifacts by a nuclear medicine physician. The apparent lung shunt fraction (nonzero due to scatter) was estimated on planar and SPECT images. Results A 20% count loss due to dead time was observed around 0.7 GBq in the photopeak window. Independent of the count losses, the measured activity concentration was up to 100% of the real value for non-tumorous liver, when reconstructions were normalized to the known activity at scanning time. However, for tumor spheres, activity concentration recovery was ~80% at the lowest activity, decreasing with increasing activity in the phantom. Measured lung shunt fractions were relatively constant over the considered activity range. Conclusions At high 166Ho count rate, all images, visually assessed, presented no artifacts, even at considerable dead time losses. A quantitative evaluation revealed the possibility of reliable dosimetry within the healthy liver, as long as a post-reconstruction scaling to scanning activity is applied. Reliable tumor dosimetry, instead, remained hampered by the dead time.

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Quantitative E. D. Analysis At High Count-Rates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134764 ◽

1990 ◽

Vol 48 (2) ◽

pp. 232-233

Author(s):

S.J.B. Reed

Keyword(s):

Quantitative Analysis ◽

Count Rate ◽

Dead Time ◽

Geological Samples ◽

Maximum Throughput ◽

Output Rate ◽

High Count ◽

Throughput Rate ◽

Lower Detection ◽

Time Required

Hitherto quantitative E.D. analysis has been carried out generally at pulse throughput rates up to about 5 kHz. Some commercially available E.D. systems are, however, now capable of rates exceeding 30 kHz. The present study is concerned with the feasibility of quantitative analysis at high count-rates, with the emphasis on applications to geological samples, especially silicates. Benefits of high count-rates include reduction in the time required per quantitative analysis. Also lower detection limits are obtainable with a constant time. Furthermore, flexibility with regard to count-rate is useful in combined E.D. and W.D. analysis.The Link Analytical XP2 pulse processor used in this study has a choice of 6 ‘process times’ (equivalent to the peaking time in a conventional amplifier). The throughput (or output) rate as a function of input count-rate for process times 1-4 is shown in Figure 1. The shortest (no. 1) gives a maximum throughput rate of 32 kHz, the dead time per pulse being 12 μS.

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SPAD pixel with sub-ns dead-time for high-count rate applications

IEEE Journal of Selected Topics in Quantum Electronics ◽

10.1109/jstqe.2021.3124825 ◽

2021 ◽

pp. 1-1

Author(s):

Fabio Severini ◽

Iris Cusini ◽

Davide Berretta ◽

Klaus Pasquinelli ◽

Alfonso Incoronato ◽

...

Keyword(s):

Count Rate ◽

Dead Time ◽

High Count ◽

High Count Rate

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Pulse Shape Processing to correct Pile up and Dead Time at High Count Rate by using Digital Spectroscopy Analyzer (DSA)

Journal of Zankoy Sulaimani - Part A ◽

10.17656/jzs.10168 ◽

2007 ◽

Vol 10 (1) ◽

pp. 113-123

Author(s):

Adil M. Hussein ◽

Keyword(s):

Count Rate ◽

Pulse Shape ◽

Dead Time ◽

High Count ◽

High Count Rate ◽

Pile Up ◽

Shape Processing

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The Dead Time of a G.M. Counter Tube

Radiochimica Acta ◽

10.1524/ract.1963.2.1.41 ◽

1963 ◽

Vol 2 (1) ◽

Cited By ~ 3

Author(s):

G. A. Brinkman

Keyword(s):

Count Rate ◽

Simple Formula ◽

Dead Time ◽

High Count ◽

Two Samples ◽

The Dead

SummaryIn this article it will be proved that the commonly used formula for dead time corrections :[xxx] (Ν' is the true and Ν the measured count rate, r the dead time) is correct for a G.M.-counter tube and also for high count-rates. However τ seem to be a function of N.Three often used methods for measuring the dead time τ are discussed (the two samples method ; the method of a series of samples in which the relative intensities are very well known; the method of a shortlived radioisotope), and also for each of these three methods the best way to calculate the dead time from the experiments. The two samples method, combined with a very simple formula ofThe theory has been illustrated by a number of experiments according to the three different methods.

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