Flat-panel Imagers Research Articles

Thermal expansion regulation of metal halide perovskites for robust flat-panel X-ray image detectors

Thermal expansion regulation of metal halide perovskites for robust flat-panel X-ray image detectors

Optimized substrate temperature for high-quality CdZnTe epitaxial film in X-ray flat panel detectors

Cadmium zinc telluride (CdZnTe or CZT) materials, favored for their physical superiority in optoelectronic applications, can be efficiently produced as large-area epitaxial film via close space sublimation (CSS), enhancing potential in flat-panel detector imaging. However, the application of CdZnTe epitaxial film in medical imaging equipment is limited by their lower resistivity, prolonged response times, and diminished sensitivity. By elevating the substrate temperature, we enhanced the number and depth of reverse sublimation pits on the surface of the CdZnTe epitaxial film, established an approximately 100 nm Zn-rich layer, broadened the bandwidth, and minimized electrode injection. Additionally, we observed an aggregation of dislocations at the edges of the reverse sublimation pits, which promoted surface recombination and reduced leakage current. These modifications significantly increased the film's resistivity to 1011 Ω cm. Further, they notably decreased the rise and drop times to 2 m s and 4 m s, respectively. Integrated with thin-film transistors (TFTs), the optimized CdZnTe epitaxial film now distinctly differentiate between air, plastics, and metals under X-ray examination. This improved performance of X-ray flat panel detectors (FPDs) based on CdZnTe epitaxial film is promising for the development of next-generation X-ray detection systems.

Improvement of X-ray response of CZT films by post-annealing

CdZnTe (CZT) epitaxial films are promising for X-ray flat panel detectors due to their ability for large area fabrication, high absorption efficiency, and excellent detective quantum efficiency (DQE). However, challenges like image lag, ghosting, and reduced DQE due to long response times and high dark currents persist. This study introduces a novel post-in-situ annealing technique to enhance CZT film sensitivity and transient response. Results show that a brief 20 s annealing treatment increased surface Zn content, raising detector resistivity from 3.5 × 109 Ω·cm to 3.3 × 1010 Ω·cm while reducing leakage current at high voltages. This treatment also significantly reduced surface defects, improving CZT film detectors’ X-ray response time. Moreover, the electrons mobility-lifetime product (μτ)e improved from 2.30 × 10−5 cm2/V to 2.17 × 10−4 cm2/V, indicating enhanced charge carrier dynamics crucial for high-speed X-ray detection. Notably, the X-ray response sensitivity achieved a commendable 126 μC G−1· cm−2 a bias of 30 V. In conclusion, in-situ annealing represents a remarkable step forward in the development of CZT technology for X-ray flat panel imaging, addressing critical issues and potentially broadening its applications in medical and industrial imaging systems.

Superior Canal Dehiscence and the Risk of Additional Dehiscences: A Retrospective CT Cohort Study.

Determine if superior canal dehiscence (SCD) found on flat-panel CT increases the risk for other defects in the otic capsule. Retrospective cohort study. Tertiary care center. One hundred ears (50 with SCD and 50 matched controls without SCD). Flat-panel CT imaging. (1) Prevalence of other dehiscences in SCD ears, (2) dehiscences in controls, and (3) otic capsule thickness in other reported dehiscence locations (cochlea-carotid, lateral semicircular canal [SCC] and mastoid, facial nerve-lateral SCC, vestibular aqueduct, posterior SCC-jugular bulb, posterior SCC-posterior fossa). Between-group comparisons were considered significant at p < 0.007 after applying the Bonferroni correction for multiple comparisons. Not including the SCD, there was a mean of 0.04 additional dehiscences in the SCD group (n = 2/50, 4%) and 0.04 non-SCD dehiscences in the controls (n = 2/50, 4%, p > 0.007). In the SCD group, there was one dehiscence between the cochlea and carotid artery and one between the posterior SCC and posterior fossa. The control group had one enlarged vestibular aqueduct and one dehiscence between the facial nerve and lateral SCC. As a group, SCD ears had wider vestibular aqueducts (0.68 ± 0.20 vs 0.51 ± 0.30 mm, p < 0.007) and thinner bone between the posterior SCC and posterior fossa (3.12 ± 1.43 vs 4.34 ± 1.67 mm, p < 0.007). The bone between the facial nerve and lateral SCC was thicker in SCD ears (0.77 ± 0.23 vs 0.55 ± 0.27 mm, p < 0.007) and no different for cochlea-carotid, and lateral SCC and mastoid (p > 0.007). SCD does not increase the likelihood of a second dehiscence in the same otic capsule. SCD patients may have congenitally thinner otic capsule bones compared to controls, particularly near the posterior SCC, where the vestibular aqueduct may be enlarged.

Optimized Gd2O2S:Pr Scintillation Films for X-ray Flat Panel Imaging: Balancing Enhanced Efficiency with Flexibility

Optimized Gd₂O₂S:Pr Scintillation Films for X-ray Flat Panel Imaging: Balancing Enhanced Efficiency with Flexibility

Flat-panel Detector Perfusion Imaging and Conventional Multidetector Perfusion Imaging in Patients with Acute Ischemic Stroke

PurposeFlat-panel detector computed tomography (FDCT) is increasingly used in (neuro)interventional angiography suites. This study aimed to compare FDCT perfusion (FDCTP) with conventional multidetector computed tomography perfusion (MDCTP) in patients with acute ischemic stroke.MethodsIn this study, 19 patients with large vessel occlusion in the anterior circulation who had undergone mechanical thrombectomy, baseline MDCTP and pre-interventional FDCTP were included. Hypoperfused tissue volumes were manually segmented on time to maximum (Tmax) and time to peak (TTP) maps based on the maximum visible extent. Absolute and relative thresholds were applied to the maximum visible extent on Tmax and relative cerebral blood flow (rCBF) maps to delineate penumbra volumes and volumes with a high likelihood of irreversible infarcted tissue (“core”). Standard comparative metrics were used to evaluate the performance of FDCTP.ResultsStrong correlations and robust agreement were found between manually segmented volumes on MDCTP and FDCTP Tmax maps (r = 0.85, 95% CI 0.65–0.94, p < 0.001; ICC = 0.85, 95% CI 0.69–0.94) and TTP maps (r = 0.91, 95% CI 0.78–0.97, p < 0.001; ICC = 0.90, 95% CI 0.78–0.96); however, direct quantitative comparisons using thresholding showed lower correlations and weaker agreement (MDCTP versus FDCTP Tmax 6 s: r = 0.35, 95% CI −0.13–0.69, p = 0.15; ICC = 0.32, 95% CI 0.07–0.75). Normalization techniques improved results for Tmax maps (r = 0.78, 95% CI 0.50–0.91, p < 0.001; ICC = 0.77, 95% CI 0.55–0.91). Bland-Altman analyses indicated a slight systematic underestimation of FDCTP Tmax maximum visible extent volumes and slight overestimation of FDCTP TTP maximum visible extent volumes compared to MDCTP.ConclusionFDCTP and MDCTP provide qualitatively comparable volumetric results on Tmax and TTP maps; however, direct quantitative measurements of infarct core and hypoperfused tissue volumes showed lower correlations and agreement.

MV-based relative electron density estimation (iMREDe) for MR-LINAC dose calculation.

MR-LINAC systems have been increasingly utilized for real-time imaging in adaptive treatments worldwide. Challenges in MR representation of air cavities and subsequent estimation of electron density maps impede planning efficiency and may lead to dose calculation uncertainties. To demonstrate the generation of accurate electron density maps using the primary MV beam with a flat-panel imager. The ViewRay MRIdian MR-LINAC system was modeled digitally for Monte Carlo simulations. Iron shimming, the magnetic field, and the proposed flat panel detector were included in the model. The effect of the magnetic field on the detector response was investigated. Acquisition of projections over 360 degrees was simulated for digital phantoms of the Catphan 505 phantom and a patient treated for Head and Neck cancer. Shim patterns on the projections were removed and detector noise linearity was assessed. Electron density maps were generated for the digital patient phantom using the flat-panel detector and compared with actual treatment planning CT generated electron density maps of the same patient. The effect of the magnetic field on the detector point-spread function (PSF) was found to be substantial for field strengths above 50 mT. Shims correction in the projection images using air normalization and in-painting effectively removed reconstruction artifacts without affecting noise linearity. The relative difference between reconstructed electron density maps from the proposed method and electron density maps generated from the treatment planning CT was 11% on average along all slices included in the iMREDe reconstruction. The proposed iMREDe technique demonstrated the feasibility of generating accurate electron densities for the ViewRay MRIdian MR-LINAC system with a flat-panel imager and the primary MV beam. This work is a step towards reducing the time and effort required for adaptive radiotherapy in the current ViewRay MR-LINAC systems.

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging.

Active matrix flat panel imagers (AMFPIs) with thin-film transistor arrays experience image quality degradation by electronic noise in low-dose radiography and fluoroscopy. One potential solution is to overcome electronic noise using avalanche gain in an amorphous selenium (a-Se) (HARP) photoconductor in indirect AMFPI. In this work, we aim to improve temporal performance of HARP using a novel composite hole blocking layer (HBL) structure and increase optical quantum efficiency (OQE) to CsI:Tl scintillators by tellurium (Te) doping. Two different HARP structures were fabricated: Composite HBL samples and Te-doped samples. Dark current and optical sensitivity measurements were performed on the composite HBL samples to evaluate avalanche gain and temporal performance. The OQE and temporal performance of the Te-doped samples were characterized by optical sensitivity measurements. A charge transport model was used to investigate the hole mobility and lifetime of the Te-doped samples in combination with time-of-flight measurements. The composite HBL has excellent temporal performance, with ghosting below 3% at 10mR equivalent exposure. Furthermore, the composite HBL samples have dark current and achieved an avalanche gain of 16. Te-doped samples increased OQE from 0.018 to 0.43 for 532nm light. The addition of Te resulted in 2.1% first-frame lag, attributed to hole trapping within the layer. The composite HBL and Te-doping can be utilized to improve upon the limitations of previously developed indirect HARP imagers, showing excellent temporal performance and increased OQE, respectively.

Abstract 148: Balloon‐assisted retrograde Cerebral Venography in Cerebral Venous Interventions: A novel avenue for diagnostic venous imaging

Introduction Angiographic imaging of cerebral venous system is derived from the delayed phase of a cerebral arteriogram. The venous phase of arteriogram provides washed out images, quality of which is determined by the direction of dominant venous outflow, iodinated contrast ratio and flat panel imaging resolution*. Direct venous injections are limited in visualization due to injections against the direction of blood flow. We identified a method of cerebral phlebography under temporary venous balloon occlusion of jugular vein or venous sinus to obtain high resolution 2D and 3D images for diagnosis and treatment of cerebral venous pathology. We propose the addition and use of large diameter compliant balloon guide catheters in the workflow of cerebral venous imaging to optimize filling of cerebral venous system and significantly improve venous imaging. Methods A case series of 15 patients who underwent Intracranial Venous Interventions were collected from the Hospital of the University of Pennsylvania. All patients underwent 2 and 3‐dimensional retrograde phlebography assisted by temporary inflation of balloon guide catheter. Results 9 females and 6 males received venous access predominantly located in right cubital fossa in the cephalic or basilic vein using an 8 and 9 french sheaths. The balloon guide catheters employed included Walrus Balloon Guide 8F (Q’apel medical) 8 cases, Dr Banner Balloon Guide ( EO solutions corp) 5 cases, Bobby Balloon guide (microvention)1 case, Emboguard Balloon Guide ( Cerenovus) 1 case. Utilization of balloon catheters resulted in minimal increase in average procedure time with improved filling and depiction of venous vessels, and no complications. Conclusion Balloon assisted retrograde phlebography using compliant balloon guide catheters is an effective way to image cerebral veins while decreasing the difficulty associated with working against the flow of venous blood.

Renal perfusion improvement in the perioperative period after unilateral endovascular revascularization in patients with atherosclerotic renal artery stenosis.

The clinical benefits of endovascular treatment in renal artery stenosis (RAS) remain controversial. This study used an intraoperative renal perfusion imaging technique, called flat-panel detector parenchymal blood volume imaging (FD-PBV), to observe the change in renal perfusion after endovascular treatment in RAS. In a prospective, single-center study, we assigned 30 patients with atherosclerotic RAS who underwent endovascular treatment between March 2016 and March 2021. The preoperative and postoperative results of renal perfusion, blood pressure, and renal function, were compared. Both median kidney volume (p < 0.001) and median preoperative mean density of contrast medium (MDCM) (p = 0.028) increased significantly after endovascular treatment. The ratio of postoperative and preoperative MDCM differed greatly among the patients. For patients with preoperative MDCM <304.0 HU (Subgroup A, 15 cases), MDCM significantly increased after treatment (p = 0.001) and 12 (80.0%) patients had more than 10% increase in renal perfusion. For patients who had relatively high preoperative renal perfusion (MDCM ≥304.0 HU, Subgroup B, 15 cases), preoperative and postoperative MDCM were similar (p = 0.776). On the other hand, the serum creatinine levels significantly decreased in Subgroup A (p = 0.033) and fewer antihypertensive drugs were used after endovascular revascularization (p = 0.041). The preoperative and postoperative creatinine levels and number of antihypertensive drugs were similar in Subgroup B. During the perioperative period, RAS patients with relatively low preoperative renal perfusion levels had greater improvement in renal perfusion, renal function, and blood pressure control after endovascular treatment. The improvement of renal function needs to be confirmed by long-term follow-up.

Impact of a novel multilayer imager on metal artifacts in MV-CBCT

Objective. Megavoltage cone-beam computed tomography (MV-CBCT) imaging offers several advantages including reduced metal artifacts and accurate electron density mapping for adaptive or emergent situations. However, MV-CBCT imaging is limited by the poor efficiency of current detectors. Here we examine a new MV imager and compare CBCT reconstructions under clinically relevant scenarios. Approach. A multilayer imager (MLI), consisting of four vertically stacked standard flat-panel imagers, was mounted to a clinical linear accelerator. A custom anthropomorphic pelvis phantom with replaceable femoral heads was imaged using MV-CBCT and kilovoltage CBCT (kV-CBCT). Bone, aluminum, and titanium were used as femoral head inserts. 8 MU 2.5 MV scans were acquired for all four layers and (as reference) the top layer. Prostate and bladder were contoured on a reference CT and transferred to the other scans after rigid registration, from which the structural similarity index measure (SSIM) was calculated. Prostate and bladder were also contoured on CBCT scans without guidance, and Dice coefficients were compared to CT contours. Main results. kV-CBCT demonstrated the highest SSIMs with bone inserts (prostate: 0.86, bladder: 0.94) and lowest with titanium inserts (0.32, 0.37). Four-layer MV-CBCT SSIMs were preserved with bone (0.75, 0.80) as compared to titanium (0.67, 0.74), outperforming kV-CBCT when metal is present. One-layer MV-CBCT consistently underperformed four-layer results across all phantom configurations. Unilateral titanium inserts and bilateral aluminum insert results fell between the bone and bilateral titanium results. Dice coefficients trended similarly, with four-layer MV-CBCT reducing metal artifact impact relative to KV-CBCT to provide better soft-tissue identification. Significance. MV-CBCT with a four-layer MLI showed improvement over single-layer MV scans, approaching kV-CBCT quality for soft-tissue contrast. In the presence of artifact-producing metal implants, four-layer MV-CBCT scans outperformed kV-CBCT by eliminating artifacts and single-layer MV-CBCT by reducing noise. MV-CBCT with a novel multi-layer imager may be a valuable alternative to kV-CBCT, particularly in the presence of metal.

Organic and Inorganic Metal Halide Tandem Scintillator for Dual-Energy Flat-Panel X-ray Imaging.

Traditional indirect flat-panel X-ray imaging (FPXI) uses inorganic scintillators with high-Z elements, which lack spectral information about X-ray photons and reflect only integrated X-ray intensity. To address this issue, we developed a stacked scintillator structure that combines organic and inorganic materials. This structure allows X-ray energies to be distinguished in a single shot by using a color or multispectral visible camera. However, the resolution of the resulting dual-energy image is primarily limited by the top scintillator layer. We inserted a layer of anodized aluminum oxide (AAO) between the double scintillators. This layer limits the lateral propagation of scintillation light, improves imaging resolution, and acts as a filter for X-rays. Our research demonstrates the advantages of stacked organic-inorganic scintillator structures for dual-energy X-ray imaging and provides novel and practical applications for relatively low-Z organic scintillators with high internal X-ray-to-light conversion efficiency.

Effect of different scintillator choices on the X-ray imaging performance of CMOS sensors

The ability of wafer scale Complementary Metal Oxide Semiconductor (CMOS) imagers to integrate sensing with analogue to digital conversion at the pixel level has led to their widespread appeal in a variety of imaging applications. This has led to significant improvement in speed and reduction in read-out noise in these imagers when compared to charge-coupled devices (CCDs) and amorphous silicon/selenium based flat panel imagers (FPIs). This paper compares the performance characteristics of CMOS X-ray detectors in various configurations by varying certain parameters of a typical X-ray detector such as fibre optic face plate (FOP), scintillator substrate coating, sensor pixel pitch and scintillator thickness. The evaluations were carried out using RQA5 (70 kV) radiation beam quality aimed at general radiography applications. At comparable Air Kerma values, detectors with a fibre optic plate showed an overall better DQE performance at most spatial frequencies, starting slightly lower at low frequencies then overtaking the “no-FOP” case at mid and high frequencies. The analysis of detectors with different substrate coatings for the scintillators showed comparatively higher DQE for the white-coated aluminium substrate scintillator compared to the black-coated one. The DQE comparison of detectors with 50μm and 100μm pixel pitch resulted in a higher DQE for the 100μm pixel pitch one, with the caveat that the scintillator was thick enough as to render differences in pMTF negligible. Finally, the comparison of scintillators with varying thicknesses showed that the thickest scintillator yielded the highest DQE. These characterisation studies helped in understanding the suitability of these different configurations in various general radiography application scenarios and could be of help to prospective users to determine the overall configuration that best fits their specific imaging needs.

Minimization of image lag in polycrystalline mercuric iodide converters through incorporation of Frisch grid structures for digital breast tomosynthesis

Objective. Polycrystalline mercuric iodide photoconductive converters fabricated using particle-in-binder techniques (PIB HgI2) provide significantly more detected charge per x-ray interaction than from a-Se and CsI:Tl converters commonly used with active matrix flat-panel imagers (AMFPIs). This enhanced sensitivity makes PIB HgI2 an interesting candidate for applications involving low x-ray exposures—since the relatively high levels of additive electronic noise exhibited by AMFPIs incorporating a-Se and CsI:Tl reduce detective quantum efficiency (DQE) performance under such conditions. A theoretical study is reported on an approach for addressing a major challenge impeding practical use of PIB HgI2 converters—the high lag exhibited by the material (over 10%) which would lead to undesirable image artifacts in applications involving acquisition of consecutive images such as digital breast tomosynthesis. Approach. Charge transport modeling accounting for the trapping and release of holes (thought to be the primary contributor to lag) was used to examine signal properties, including lag, of pillar-supported Frisch grids embedded in the photoconductor for 100 μm pitch AMFPI pixels. Performance was examined as a function of electrode voltage, grid pitch (center-to-center distance between neighboring grid wires) and the ratio of grid wire width to grid pitch. Main results. Optimum grid designs maximizing suppression of signal generated by hole transport, without significantly affecting the total signal due to electron and hole transport, were identified and MTF was determined. For the most favorable designs, additional modeling was used to determine DQE. The results indicate that, through judicious choice of grid design and operational conditions, first frame lag can be significantly reduced to below 1%—less than the low levels exhibited by a-Se. DQE performance is shown to be largely maintained as exposure decreases—which should help to maintain good image quality. Significance. Substantial reduction of lag in PIB HgI2 converters via incorporation of Frisch grids has been demonstrated through modeling.

Next generation high resolution perovskite direct conversion detector: Monte Carlo design optimisation and virtual clinical trial

We implement virtual clinical integration of next-generation perovskite detectors into common x-ray imaging devices. This was achieved by performing Monte Carlo (MC) optimisation of the design and benchmarking of low cost, high spatial resolution, direct conversion perovskite crystal x-ray flat panel imagers for a next generation of breast-, MV-, and kV-cone beam CT detectors. Semiconductor methylammonium lead bromide perovskite crystals energy deposition efficiencies calculated in TOPAS were benchmarked against four common detector materials for twelve detector crystal thicknesses between 40 to 15 mm and ten beam energies ranging from 20 keV to 6 MeV. Based on these simulations, Koning's dedicated breast CT, and Varian's Truebeam kV- and MV-cone beam CT systems were designated as suitable applications for perovskite detectors. System specific Fastcat hybrid MC cone beam CT image simulation was subsequently used to optimise the perovskite detector design and conduct virtual clinical trials. Device-specific optimal perovskite crystal thicknesses were calculated to be 0.30, 0.86, and 1.99 mm for Koning breast CT and Truebeam kV- and MV-cone beam CT systems, respectively. Replacing the current detectors on these machines with low cost perovskite crystal detectors could be advantageous as it would simultaneously yield 12.1%, 9.5% and 86.1% improvements in detective quantum efficiency as well as increases in contrast to noise ratio in brain, lung, and bone tissues.

Arthroscopic defect size measurement in osteochondral lesions of the talus underestimates the exact defect size and size measurement with arthro-MRI (MR-A) and high-resolution flat-panel CT-arthro imaging (FPCT-A).

The size of osteochondral lesions of the talus (OLTs) is highly relevant for their treatment. In addition to intraoperative measurement of defect size, preoperative planning by means of magnetic resonance imaging (MRI) or computed tomography (CT) is crucial. Four defects of different sizes and depths were created on the talar joint surface in 14 cadaver feet. All defects were evaluated, both arthroscopically and via arthrotomy with a probe. Arthro-MRI (MR-A) and high-resolution flat-panel CT arthro scans (FPCT-A) were acquired. Length, width, and depth were measured for every defect and the defect volume was calculated. To determine the exact defect size, each talar defect was filled with plastic pellets to form a cast and the casts were scanned using FPCT to create a 3D multiplanar reconstruction data set. Finally, the surgically measured values were compared with the radiological values and the exact defect size. Overall, the surgically measured values (both arthroscopic and open) underestimated the exact defect size (p < 0.05). Arthroscopically determined defect length and width showed the largest deviation (p < 0.05) and underestimated the size in comparison with MR-A and FPCT-A. The FPCT-A measurements demonstrated higher correlation with both the arthroscopic and open surgical measurements than did the MR-A measurements (p < 0.05). The exact defect size is underestimated on intraoperative measurement, in both arthroscopic and open approaches. Arthroscopic defect size measurement underestimates defect size in comparison with MR-A and FPCT-A. FPCT-A was shown to be a reliable imaging technique that allows free image reconstruction in every plane and could be considered as the new reference standard for preoperative evaluation of defect size in OLT.

Multispectral Large-Panel X-ray Imaging Enabled by Stacked Metal Halide Scintillators.

Conventional energy-integration black-white X-ray imaging lacks the spectral information of X-ray photons. Although X-ray spectra (energy) can be distinguished by the photon-counting technique typically with CdZnTe detectors, it is very challenging to be applied to large-area flat-panel X-ray imaging (FPXI). Herein, multilayer stacked scintillators of different X-ray absorption capabilities and scintillation spectra are designed; in this scenario, the X-ray energy can be discriminated by detecting the emission spectra of each scintillator; therefore, multispectral X-ray imaging can be easily obtained by color or multispectral visible-light camera in a single shot of X-rays. To verify this idea, stacked multilayer scintillators based on several emerging metal halides are fabricated in a cost-effective and scalable solution process, and proof-of-concept multispectral (or multi-energy) FPXI are experimentally demonstrated. The dual-energy X-ray image of a "bone-muscle" model clearly shows the details that are invisible in conventional energy-integration FPXI. By stacking four layers of specifically designed multilayer scintillators with appropriate thicknesses, a prototype FPXI with four energy channels is realized, proving its extendibility to multispectral or even hyperspectral X-ray imaging. This study provides a facile and effective strategy to realize multispectral large-area flat-panel X-ray imaging.

Tuning the Photon Sensitization Mechanism in Metal‐Halide‐Perovskite‐Based Nanocomposite Films Toward Highly Efficient and Stable X‐Ray Detection

AbstractMetal halide perovskites (MHPs) have emerged as promising X‐ray detection materials. However, most MHP‐based X‐ray detectors are incompatible for large‐area preparation and integration, and suffer from the serious ion migration issue. This work demonstrates a “perovskite‐in‐a‐host” nanocomposite structure for X‐ray detection, by embedding the perovskite nanocrystal (PNC) sensitizers in the organic interpenetrating charge transport channels to work as the X‐ray attenuation layer. Intriguingly, the photon sensitization mechanism can be readily tuned from indirect‐ to direct‐type X‐ray conversion by decreasing the ligand density on the PNC surface, which significantly increases the sensitivity to 5 696 µC Gyair–1 cm–2. Besides, the ion migration gets suppressed due to the ion blocking effect of the surrounding organic phase. Therefore, an ultra‐small dark current relative drift of 3.57 × 10–9 cm s–1 V–1 is achieved even under an extremely large electric field up to 5 100 V cm–1, ensuring a low detection limit down to 72 nGyair s–1. The superior sensitivity and biasing stability enable the high performance X‐ray imaging capability of the devices, which exhibit great potential in scaling up and integration for the flat panel imaging.

Comparison of Calculated Skin Doses in Cineradiography and Four Dimensional Kinematic Computed Tomography of the Wrist.

Background: Previous studies have discussed the diagnostic value of four dimensional kinematic CT in cases of carpal instabilities. This analysis compares calculated skin doses of 4D CT and conventional cineradiography of the wrist in cases of suspected SLL rupture. Methods: Retrospective calculation and interpolation of skin doses and effective doses for ten consecutive 4D CT examinations and 41 cineradiographies for suspected lesions of the scapholunate ligament. Standardised anterior-posterior and lateral cine sequences using a flat-panel digital subtraction imager and of 4D kinematic CT using a dual-source scanner were acquired and acquisition parameters recorded. We tested if the skin dose of 4D CT is different from cineradiography. Results: Median dose area product (DAP) of cineradiography was 135.34 cGycm2 resulting in a calculated median skin dose of 32.6 mSv (confidence interval 26.86-42.90 mSv) and an estimated effective skin dose of 3.26 µSv. CT dose index (CTDI) for 4D examinations was recorded to be 26.79 mGy and the dose-length product (DLP) was 150 mGy × cm. This resulted in an estimated skin dose of 34 mSv, which is covered by the confidence interval of cineradiography, and an effective skin dose of 3.4 µSv. Conclusions: Skin dose calculations are comparable for 2D cineradiography in two plains and 4D kinematic CT of the wrist. Calculated effective doses are < 0.01 mSv.

Beam's-Eye-View Imaging of Liver SBRT With a Novel Multi-Layer Imager

Beams-eye view (BEV) imaging during radiation therapy can be used for real-time localization of the treatment target. However, clinical implementation is limited by the poor performance of current electronic portal imaging devices (EPIDs). A novel multilayer imager (MLI), consisting of four stacked conventional flat-panel imagers, was recently shown to have 5.7 times the detective quantum efficiency and nearly 2 times the contrast-to-noise ratio of a conventional EPID. In the current study, we compare the MLI against a single layer imager for the application of fiducial tracking during liver SBRT procedures. The hypothesis is that the MLI will provide more accurate and efficient fiducial tracking.The prototype MLI was installed in the standard MV imager housing on a clinical LINAC, replacing the conventional EPID. The MV imager arm was extended during volumetric modulated arc therapy (VMAT) SBRT treatments for passive data acquisition. Six patients with liver metastases receiving SBRT in 3-5 fractions (900-1200 cGy/fx) were studied. Data was acquired for two fractions of each treatment course, one fraction with the MLI using all 4 layers and one with the MLI using the top layer only. Automatic fiducial localization was performed using a modification of a previously published algorithm. Truth data was derived using external surrogate respiratory traces combined with manual tracking. Results for 4- and 1-layer modes were compared against truth data to determine tracking accuracy and efficiency. Tracking and noise improvements were assessed for any correlation.Between 2771 to 6505 image frames were acquired for each patient, with roughly half of each corresponding to acquisition in 1-layer mode and the other half 4-layer mode. Tracking accuracy with the 1-layer imager returned a root mean square error (RMSE) of 2.1 mm compared to 4-layer RMSE of 1.5 mm, a statistically significant (P < 0.001) improvement of 0.6 mm. Successful tracking efficiency with 4 layers improved to 82.8% versus 58.4% for the 1-layer mode, a relative improvement of 41.8% (P < 0.001). There was a strong correlation (r = 0.913) between the increase in successfully tracked frames and reduction in noise when using the 4-layer mode.Noise reduction and increased MV photon detection efficiency achieved by utilizing a multi-layer MV imager results in improved fiducial tracking for liver SBRT treatments. Future BEV clinical applications may be improved by pursuing similar noise reduction and photon detection enhancement strategies.