Photon Counting Research Articles

Ultra-High Spatial Resolution Images of the Temporal Bone Obtained With a Newly Released Photon-Counting Detector Computed Tomography.

Ultra-High Spatial Resolution Images of the Temporal Bone Obtained With a Newly Released Photon-Counting Detector Computed Tomography.

Myelography Using Energy-Integrating Detector CT Versus Photon-Counting Detector CT for Detection of CSF-Venous Fistulas in Patients With Spontaneous Intracranial Hypotension.

BACKGROUND. CSF-venous fistulas (CVFs), which are an increasingly recognized cause of spontaneous intracranial hypotension (SIH), are often diminutive in size and exceedingly difficult to detect by conventional imaging. OBJECTIVE. This purpose of this study was to compare energy-integrating detector (EID) CT myelography and photon-counting detector (PCD) CT myelography in terms of image quality and diagnostic performance for detecting CVFs in patients with SIH. METHODS. This retrospective study included 38 patients (15 men and 23 women; mean age, 55 ± 10 [SD] years) with SIH who underwent both clinically indicated EID CT myelography (slice thickness, 0.625 mm) and PCD CT myelography (slice thickness, 0.2 mm; performed in ultrahigh-resolution mode) to assess for CSF leak. Three blinded radiologists reviewed examinations in random order, assessing image noise, discernibility of spinal nerve root sleeves, and overall image quality (each assessed using a scale of 0-100, with 100 denoting highest quality) and recording locations of the CVFs. Definite CVFs were defined as CVFs described in CT myelography reports using unequivocal language and having an attenuation value greater than 70 HU. RESULTS. For all readers, PCD CT myelography, in comparison with EID CT myelography, showed higher mean image noise (reader 1: 69.9 ± 18.5 [SD] vs 37.6 ± 15.2; reader 2: 59.5 ± 8.7 vs 49.3 ± 12.7; and reader 3: 57.6 ± 13.2 vs 42.1 ± 16.6), higher mean nerve root sleeve discernibility (reader 1: 81.6 ± 21.7 [SD] vs 30.4 ± 13.6 reader 2: 83.6 ± 10 vs 70.1 ± 18.9; and reader 3: 59.6 ± 13.5 vs 50.5 ± 14.4), and higher mean overall image quality (reader 1: 83.2 ± 20.0 [SD] vs 38.1 ± 13.5; reader 2: 80.1 ± 10.1 vs 72.4 ± 19.8; and reader 3: 57.8 ± 11.2 vs 51.9 ± 13.6) (all p < .05). Eleven patients had a definite CVF. Sensitivity and specificity of EID CT myelography and PCD CT myelography for the detection of definite CVF were 45% and 96% versus 64% and 85%, respectively, for reader 1; 36% and 100% versus 55% and 96%, respectively, for reader 2; and 57% and 100% versus 55% and 93%, respectively, for reader 3. The sensitivity was significantly higher for PCD CT myelography than for EID CT myelography for reader 1 and reader 2 (both p < .05) and was not significantly different between the two techniques for reader 3 (p = .45); for all three readers, specificity was not significantly different between the two modalities (all p > .05). CONCLUSION. In comparison with EID CT myelography, PCD CT myelography yielded significantly improved image quality with significantly higher sensitivity for CVFs (for two of three readers), without significant loss of specificity. CLINICAL IMPACT. The findings support a potential role for PCD CT myelography in facilitating earlier diagnosis and targeted treatment of SIH, avoiding high morbidity during potentially prolonged diagnostic workups.

Influence of helical pitch and gantry rotation time on image quality and file size in ultrahigh-resolution photon-counting detector CT

The goal of this experimental study was to quantify the influence of helical pitch and gantry rotation time on image quality and file size in ultrahigh-resolution photon-counting CT (UHR-PCCT). Cervical and lumbar spine, pelvis, and upper legs of two fresh-frozen cadaveric specimens were subjected to nine dose-matched UHR-PCCT scan protocols employing a collimation of 120 × 0.2 mm with varying pitch (0.3/1.0/1.2) and rotation time (0.25/0.5/1.0 s). Image quality was analyzed independently by five radiologists and further substantiated by placing normed regions of interest to record mean signal attenuation and noise. Effective mAs, CT dose index (CTDIvol), size-specific dose estimate (SSDE), scan duration, and raw data file size were compared. Regardless of anatomical region, no significant difference was ascertained for CTDIvol (p ≥ 0.204) and SSDE (p ≥ 0.240) among protocols. While exam duration differed substantially (all p ≤ 0.016), the lowest scan time was recorded for high-pitch protocols (4.3 ± 1.0 s) and the highest for low-pitch protocols (43.6 ± 15.4 s). The combination of high helical pitch and short gantry rotation times produced the lowest perceived image quality (intraclass correlation coefficient 0.866; 95% confidence interval 0.807–0.910; p < 0.001) and highest noise. Raw data size increased with acquisition time (15.4 ± 5.0 to 235.0 ± 83.5 GByte; p ≤ 0.013). Rotation time and pitch factor have considerable influence on image quality in UHR-PCCT and must therefore be chosen deliberately for different musculoskeletal imaging tasks. In examinations with long acquisition times, raw data size increases considerably, consequently limiting clinical applicability for larger scan volumes.

Photon counting Raman spectroscopy: a benchmarking study vs surface plasmon enhancement

We demonstrate a single-photon counting Raman spectroscope and benchmark it against conventional and surface-enhanced Raman spectroscopy. For direct comparison without ambiguity, we use the same solutions of Rhodamine 6G and a common optical setup with either a spectrometer or an acousto-optic tunable filter, whereas the surface enhancement is realized with immobilized Ag nanoparticles. Our results find that the single photon counting significantly elevates the detection sensitivity by up to eight orders of magnitude, arriving at a comparable level of surface-enhanced Raman spectroscopy. Another significant advantage is with the time-resolving measurement, where we demonstrate time-gated and time-correlated single-photon counting with sub-nanosecond resolution. It offers insights into the samples’ transient responses and enables the isolation of Raman scattering from fluorescence signals.

Photon-Counting Detector Computed Tomography (PCD-CT): A New Era for Cardiovascular Imaging? Current Status and Future Outlooks.

Photon-counting detector computed tomography (PCD-CT) represents a revolutionary new generation of computed tomography (CT) for the imaging of patients with cardiovascular diseases. Since its commercial market introduction in 2021, numerous studies have identified advantages of this new technology in the field of cardiovascular imaging, including improved image quality due to an enhanced contrast-to-noise ratio, superior spatial resolution, reduced artifacts, and a reduced radiation dose. The aim of this narrative review was to discuss the current scientific literature, and to find answers to the question of whether PCD-CT has yet led to a true step-change and significant progress in cardiovascular imaging.

Superconducting nanostrip single photon detectors fabricated of aluminum thin-films

We systematically investigated the detection performance of Al nanostrips for single photons at various wavelengths. The Al films were deposited using magnetron sputtering, and the sophisticated nanostructures and morphology of the deposited films were revealed through high-resolution transmission electron microscopy. The fabricated Al meander nanostrips, with a thickness of 4.2 nm and a width of 178 nm, exhibited a superconducting transition temperature of 2.4 K and a critical current of approximately 5 μA at 0.85 K. While the Al nanostrips demonstrated a saturated internal quantum efficiency for 405-nm photons, the internal detection efficiency exhibited an exponential dependence on bias current without any saturation tendency for 1550-nm photons. This behavior can be attributed to the relatively large diffusion coefficient and coherence length of the Al films. By further narrowing the nanostrip width, the Al-SNSPDs remain capable of effectively detecting single telecom photons to facilitate practical applications.

Characterization of quasiparticle relaxation times in microstrips of NbReN for perspective applications for superconducting single-photon detectors

The study of the flux-flow instability in superconducting materials has recently gained renewed attention due to its potential implications for the use of the analyzed materials as micrometer-sized superconducting detectors for single photons. The values of the quasiparticle relaxation time (τE) measured for these detectors are affected by pinning properties. Here, we report electric transport properties of NbReN microstrips of different quality. For the strip characterized by high resistivity, and large critical currents and pinning, we estimate a value of τE that is almost two orders of magnitude larger compared to that of another strip with a smaller value for the critical current, for which we measure τE∼12 ps. This low value is comparable to those reported in the literature for microstrips made of other highly-disordered superconductors. Our results suggest that NbReN microstrips have great potential for the realization of superconducting single-photon detectors, depending on further optimization of their fabrication process and the superconducting properties affected by it.

Spectral Photon-Counting Computed Tomography: Technical Principles and Applications in the Assessment of Cardiovascular Diseases.

Spectral Photon-Counting Computed Tomography (SPCCT) represents a groundbreaking advancement in X-ray imaging technology. The core innovation of SPCCT lies in its photon-counting detectors, which can count the exact number of incoming x-ray photons and individually measure their energy. The first part of this review summarizes the key elements of SPCCT technology, such as energy binning, energy weighting, and material decomposition. Its energy-discriminating ability represents the key to the increase in the contrast between different tissues, the elimination of the electronic noise, and the correction of beam-hardening artifacts. Material decomposition provides valuable insights into specific elements' composition, concentration, and distribution. The capability of SPCCT to operate in three or more energy regimes allows for the differentiation of several contrast agents, facilitating quantitative assessments of elements with specific energy thresholds within the diagnostic energy range. The second part of this review provides a brief overview of the applications of SPCCT in the assessment of various cardiovascular disease processes. SPCCT can support the study of myocardial blood perfusion and enable enhanced tissue characterization and the identification of contrast agents, in a manner that was previously unattainable.

A Method to Correct the Temporal Drift of Single-Photon Detectors Based on Asynchronous Quantum Ghost Imaging.

Single-photon detection and timing has attracted increasing interest in recent years due to their necessity in the field of quantum sensing and the advantages of single-quanta detection in the field of low-level light imaging. While simple bucket detectors are mature enough for commercial applications, more complex imaging detectors are still a field of research comprising mostly prototype-level detectors. A major problem in these detectors is the implementation of in-pixel timing circuitry, especially for two-dimensional imagers. One of the most promising approaches is the use of voltage-controlled ring resonators in every pixel. Each of these runs independently based on a voltage supplied by a global reference. However, this yields the problem that the supply voltage can change across the chip which, in turn, changes the period of the ring resonator. Due to additional parasitic effects, this problem can worsen with increasing measurement time, leading to drift in the timing information. We present here a method to identify and correct such temporal drifts in single-photon detectors based on asynchronous quantum ghost imaging. We also show the effect of this correction on recent quantum ghost imaging (QGI) measurement from our group.

Improving photon number resolvability of a superconducting nanowire single-photon detector array using a level comparator circuit

Photon number resolving (PNR) capability is very important in many optical applications, including quantum information processing, fluorescence detection, and few-photon-level ranging and imaging. Superconducting nanowire single-photon detectors (SNSPDs) with a multipixel interleaved architecture give the array an excellent spatial PNR capability. However, the signal-to-noise ratio (SNR) of the PNR (SNRPNR) of the array will be degraded with increasing the element number due to the electronic noise in the readout circuit, which limits the PNR resolution as well as the maximum PNR number. In this study, a 16-element interleaved SNSPD array was fabricated, and the PNR capability of the array was investigated and analyzed. By introducing a level comparator circuit (LCC), the SNRPNR of the detector array was improved over a factor of four. In addition, we performed a statistical analysis of the photon number on this SNSPD array with LCC, showing that the LCC method effectively enhances the PNR resolution. Besides, the system timing jitter of the detector was reduced from 90 ps to 72 ps due to the improved electrical SNR.

The SRG/eROSITA All-Sky Survey. Dark Energy Survey year 3 weak gravitational lensing by eRASS1 selected galaxy clusters

Number counts of galaxy clusters across redshift are a powerful cosmological probe if a precise and accurate reconstruction of the underlying mass distribution is performed -- a challenge called mass calibration. With the advent of wide and deep photometric surveys, weak gravitational lensing (WL) by clusters has become the method of choice for this measurement. We measured and validated the WL signature in the shape of galaxies observed in the first three years of the Dark Energy Survey (DES Y3) caused by galaxy clusters and groups selected in the first all-sky survey performed by SRG (Spectrum Roentgen Gamma)/eROSITA (eRASS1). These data were then used to determine the scaling between the X-ray photon count rate of the clusters and their halo mass and redshift. We empirically determined the degree of cluster member contamination in our background source sample. The individual cluster shear profiles were then analyzed with a Bayesian population model that self-consistently accounts for the lens sample selection and contamination and includes marginalization over a host of instrumental and astrophysical systematics. To quantify the accuracy of the mass extraction of that model, we performed mass measurements on mock cluster catalogs with realistic synthetic shear profiles. This allowed us to establish that hydrodynamical modeling uncertainties at low lens redshifts ($z&lt;0.6$) are the dominant systematic limitation. At high lens redshift, the uncertainties of the sources' photometric redshift calibration dominate. With regard to the X-ray count rate to halo mass relation, we determined its amplitude, its mass trend, the redshift evolution of the mass trend, the deviation from self-similar redshift evolution, and the intrinsic scatter around this relation. The mass calibration analysis performed here sets the stage for a joint analysis with the number counts of eRASS1 clusters to constrain a host of cosmological parameters. We demonstrate that WL mass calibration of galaxy clusters can be performed successfully with source galaxies whose calibration was performed primarily for cosmic shear experiments, opening the way for the cluster cosmological exploitation of future optical and NIR surveys like Euclid and LSST.

Superconducting single photon detector with speed of 5 GHz and photon number resolution of 61

Superconducting single photon detector with speed of 5 GHz and photon number resolution of 61

Monolithically Integrated SiON Photonic Circuit and Silicon Single-Photon Detectors for NIR-Range Operation

Monolithically Integrated SiON Photonic Circuit and Silicon Single-Photon Detectors for NIR-Range Operation

Improvements of readout signal integrity in mid-infrared superconducting nanowire single-photon detectors

Improvements of readout signal integrity in mid-infrared superconducting nanowire single-photon detectors

Design of a Room-Temperature, Sine-Wave Gated, InGaAs/InP SPAD Based Photon Counting System With Dead-Time Mitigation

Design of a Room-Temperature, Sine-Wave Gated, InGaAs/InP SPAD Based Photon Counting System With Dead-Time Mitigation

Research on Ultraviolet Characteristic Parameters of DC-Positive Polarity Corona Discharge on Conductors

The detection of corona-related defects in transmission lines has been included in the work of transmission line defect detection. Ultraviolet detection technology has gradually been widely applied in the field of corona discharge detection. However, the current research on the application of ultraviolet detection technology in transmission lines is relatively simple and mainly limited to using changes in the photon count to determine whether corona discharge has occurred. To address this, this study used a mini corona cage to simulate transmission lines and measured the changes in the photon count, spot area, and corona current in the corona inception process of different types of smooth, stainless-steel conductors. This study also investigated the variations in the photon count and spot area depending on conductor corona intensity, ultraviolet imager gain, and observation distance. The results show that the photon count and spot area can, to some extent, reflect the intensity of corona discharge. Both the photon count and spot area exhibited quadratic relationships with the voltage. As the observation distance increased, both the photon count and spot area showed exponential decay. The photon count exhibited a trend of initially increasing, then decreasing, and finally increasing again with the increase of gain, while the spot area showed exponential growth with increasing gain. The photon count and spot area can complement each other to identify and characterize the intensity of corona discharge.

Free-space coupled, large-active-area superconducting microstrip single-photon detector for photon-counting time-of-flight imaging

Numerous applications at the photon-starved regime require a free-space coupling single-photon detector with a large active area, low dark count rate (DCR), and superior time resolutions. Here, we developed a superconducting microstrip single-photon detector (SMSPD), with a large active area of 260 µm in diameter, a DCR of ∼5kcps, and a low time jitter of ∼171ps, operated at a near-infrared of 1550 nm and a temperature of ∼2.0K. As a demonstration, we applied the detector to a single-pixel galvanometer scanning system and successfully reconstructed the object information in depth and intensity using a time-correlated photon counting technology.

Superconducting nanowire single-photon detector with polarization insensitivity, ultrafast response, and high efficiency

This study proposed what we believe to be a novel method for fabricating superconducting nanowire single-photon detectors (SNSPDs) with high efficiency, polarization insensitivity, and ultrafast response. To achieve these properties in niobium nitride (NbN) SNSPDs, the periodic four-split rings (PFSR) were positioned above the nanowires. This design uses the localized surface plasmon resonance to enhance the electric field around nanowires. For an incident light with a wavelength of 1550 nm, the PFSR-SNSPD structure achieved a polarization extinction ratio of 1.0064 and absorptions of 88.94% and 88.37% under TE and TM polarizations, respectively. The nanowire length was reduced by 85% using a meandering nanowire arrangement with a fill factor of 0.074.

Intra- and Intermolecular Charge-Transfer Dynamics of Carbene-Metal-Amide Photosensitizers.

A series of steady-state and time-resolved spectroscopies were performed on a set of eight carbene-metal-amide (cMa) complexes, where M = Cu and Au, that have been used as photosensitizers for photosensitized electrocatalytic reactions. Using ps-to-ns and ns-to-ms transient absorption spectroscopies (psTA and nsTA, respectively), the excited-state kinetics from light absorption, intersystem crossing (ISC), and eventually intermolecular charge transfer were thoroughly characterized. Using time-correlated single photon counting (TCSPC) and psTA with a thermally activated delayed fluorescence (TADF) model, the variation in intersystem crossing (ISC), (S1 → T1) rates (∼3-120 × 109 s-1), and ΔEST values (73-115 meV) for these compounds were fully characterized, reflecting systematic changes to the carbene, carbazole, and metal. The psTA additionally revealed an early time relaxation (rate ∼0.2-0.8 × 1012 s-1) attributed to solvent relaxation and vibrational cooling. The nsTA experiments for a gold-based cMa complex demonstrated efficient intermolecular charge transfer from the excited cMa to an electron acceptor. Pulse radiolysis and bulk electrolysis experiments allowed us to identify the character of the transient excited states as ligand-ligand charge transfer as well as the spectroscopic signature of oxidized and reduced forms of the cMa photosensitizer.

Cellular Imaging and Time-Domain FLIM Studies of Meso-Tetraphenylporphine Disulfonate as a Photosensitising Agent in 2D and 3D Models.

Fluorescence lifetime imaging (FLIM) and confocal fluorescence studies of a porphyrin-based photosensitiser (meso-tetraphenylporphine disulfonate: TPPS2a) were evaluated in 2D monolayer cultures and 3D compressed collagen constructs of a human ovarian cancer cell line (HEY). TPPS2a is known to be an effective model photosensitiser for both Photodynamic Therapy (PDT) and Photochemical Internalisation (PCI). This microspectrofluorimetric study aimed firstly to investigate the uptake and subcellular localisation of TPPS2a, and evaluate the photo-oxidative mechanism using reactive oxygen species (ROS) and lipid peroxidation probes combined with appropriate ROS scavengers. Light-induced intracellular redistribution of TPPS2a was observed, consistent with rupture of endolysosomes where the porphyrin localises. Using the same range of light doses, time-lapse confocal imaging permitted observation of PDT-induced generation of ROS in both 2D and 3D cancer models using fluorescence-based ROS together with specific ROS inhibitors. In addition, the use of red light excitation of the photosensitiser to minimise auto-oxidation of the probes was investigated. In the second part of the study, the photophysical properties of TPPS2a in cells were studied using a time-domain FLIM system with time-correlated single photon counting detection. Owing to the high sensitivity and spatial resolution of this system, we acquired FLIM images that enabled the fluorescence lifetime determination of the porphyrin within the endolysosomal vesicles. Changes in the lifetime dynamics upon prolonged illumination were revealed as the vesicles degraded within the cells.