Andrea Nitrosi

On site evaluation of three flat panel detectors for digital radiography.

During a tender we evaluated the image performance of three commercially available active matrix flat panel imagers (AMFPI) for general radiography, one based on direct detection method (Se photoconductor) the other two on indirect detection method (CsI phosphor). Basic image quality parameters (MTF, NNPS, DQE) were evaluated with particular attention to dose and energy dependence. As it is known, presampling modulation transfer function (MTF) of selenium based detector is very high (at 70 kV, 2 cycles/mm, 2.5 microGy, about 0.80). Indirect detection panels exhibit a comparable (lower) resolution (at 70 kV, 2 cycles/mm, 2.5 microGy, MTF is about 0.34 for both the systems analyzed) and a more pronounced energy and dose dependence could also be noted in one of them. As a consequence of the very high resolution, the normalized noise power spectrum (NNPS) of the direct system is substantially flat, very similar to a white noise. Considering that the sensitive layer of all detectors is the same (0.5 mm), the relatively higher NNPS values are related to selenium absorption properties (lower Z respect to CsI:Tl) and detector inherent noise. NNPSs of the other systems, at low frequencies, are comparable but the frequency dependence is significantly different. At 70 kV, 2.5 microGy, 0.5 cycles/mm detective quantum efficiency (DQE) is about 0.35 for the direct detection system, and about the same (0.6) for the indirect ones. The combined effect of additive and multiplicative noise components makes DQE dependence on dose not monotonic. DQE present a maximum for an intermediate exposure. This complex behavior may be useful to characterize the systems in terms of the monodimensional integral over the frequency of DQE (IDQE). Both visual contrast-detail experiment and the direct evaluation of the signal-to-noise ratio confirmed, at least in a qualitative way, the system performances predicted by IDQE.

Contrast-detail analysis of three flat panel detectors for digital radiography

In this paper we performed a contrast detail analysis of three commercially available flat panel detectors, two based on the indirect detection mechanism (GE Revolution XQ/i, system A, and Trixell/Philips Pixium 4600, system B) and one based on the direct detection mechanism (Hologic DirectRay DR 1000, system C). The experiment was conducted using standard x-ray radiation quality and a widely used contrast-detail phantom. Images were evaluated using a four alternative forced choice paradigm on a diagnostic-quality softcopy monitor. At the low and intermediate exposures, systems A and B gave equivalent performances. At the high dose levels, system A performed better than system B in the entire range of target sizes, even though the pixel size of system A was about 40% larger than that of system B. At all the dose levels, the performances of the system C (direct system) were lower than those of system A and B (indirect systems). Theoretical analyses based on the Perception Statistical Model gave similar predicted SNRT values corresponding to an observer efficiency of about 0.08 for systems A and B and 0.05 for system C.

Comparison of different computed radiography systems: Physical characterization and contrast detail analysis

PURPOSE In this study, five different units based on three different technologies-traditional computed radiography (CR) units with granular phosphor and single-side reading, granular phosphor and dual-side reading, and columnar phosphor and line-scanning reading-are compared in terms of physical characterization and contrast detail analysis. METHODS The physical characterization of the five systems was obtained with the standard beam condition RQA5. Three of the units have been developed by FUJIFILM (FCR ST-VI, FCR ST-BD, and FCR Velocity U), one by Kodak (Direct View CR 975), and one by Agfa (DX-S). The quantitative comparison is based on the calculation of the modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Noise investigation was also achieved by using a relative standard deviation analysis. Psychophysical characterization is assessed by performing a contrast detail analysis with an automatic reading of CDRAD images. RESULTS The most advanced units based on columnar phosphors provide MTF values in line or better than those from conventional CR systems. The greater thickness of the columnar phosphor improves the efficiency, allowing for enhanced noise properties. In fact, NPS values for standard CR systems are remarkably higher for all the investigated exposures and especially for frequencies up to 3.5 lp/mm. As a consequence, DQE values for the three units based on columnar phosphors and line-scanning reading, or granular phosphor and dual-side reading, are neatly better than those from conventional CR systems. Actually, DQE values of about 40% are easily achievable for all the investigated exposures. CONCLUSIONS This study suggests that systems based on the dual-side reading or line-scanning reading with columnar phosphors provide a remarkable improvement when compared to conventional CR units and yield results in line with those obtained from most digital detectors for radiography.

A comparison of digital radiography systems in terms of effective detective quantum efficiency

PURPOSE The purpose of this study is to compare digital radiography systems using the metric effective detective quantum efficiency (eDQE), which better reflects digital radiography imaging system performance under clinical operating conditions, in comparison with conventional metrics such as modulation transfer function (MTF), normalized noise power spectra (NNPS), and detective quantum efficiency (DQE). METHODS The eDQE was computed by the calculation of the MTF, the NNPS, the phantom attenuation and scatter, and estimation of x-ray flux. The physical characterization of the systems was obtained with the standard beam conditions RQA5 and RQA9, using the PA Chest phantom proposed by AAPM Report # 31 simulating the attenuation and scatter characteristics of the adult human thorax. The MTF (eMTF) was measured by using an edge test placed at the frontal surface of the phantom, the NNPS (eNNPS) was calculated from images of the phantom acquired at three different exposure levels covering the operating range of the system (E(0), which is the exposure at which a system is normally operated, 1/3 E(0), and 3 E0), and scatter measurements were assessed by using a beam-stop technique. The integral of DQE (IDQE) and eDQE (IeDQE) was calculated over the whole spatial frequency range. RESULTS The eMTF results demonstrate degradation due to magnification and the presence of scattered radiation. The eNNPS was influenced by the grid presence, and in some systems, it contained structured noise. At typical clinical exposure levels, the magnitude of eDQE(0) with respect to DQE(0) at RQA9 beam conditions was 13%, 17%, 16%, 36%, and 24%, respectively, for Carestream DRX-1, Carestream DRX-1C, Carestream Direct View CR975, Philips Digital Diagnost VM, and GE Revolution XR/d. These results were confirmed by the ratio of IeDQE and IDQE in the same conditions. CONCLUSIONS The authors confirm the robustness and reproducibility of the eDQE method. As expected, the DR systems performed better than the CR systems due to their superior signal-to-noise transfer characteristics. The results of this study suggest the eDQE method may provide an opportunity to more accurately assess the clinical performance of digital radiographic imaging systems by accounting for factors such as the presence of scatter, use of an antiscatter grid, and magnification and focal spot blurring effects, which are not reflected in conventional DQE measures.

Characterization of a clinical unit for digital radiography based on irradiation side sampling technology

PURPOSE A characterization of a clinical unit for digital radiography (FUJIFILM FDR D-EVO) is presented. This system is based on the irradiation side sampling (ISS) technology and can be equipped with two different scintillators: one traditional gadolinium-oxysulphide phosphor (GOS) and a needle structured cesium iodide (CsI) phosphor panel. METHODS The characterization was achieved in terms of response curve, modulation transfer function (MTF), noise power spectra (NPS), detective quantum efficiency (DQE), and psychophysical parameters (contrast-detail analysis with an automatic reading of CDRAD images). For both scintillation screens the authors accomplished the measurements with four standard beam conditions: RAQ3, RQA5, RQA7, and RQA9. RESULTS At the Nyquist frequency (3.33 lp/mm) the MTF is about 35% and 25% for CsI and GOS detectors, respectively. The CsI scintillator has better noise properties than the GOS screen in almost all the conditions. This is particularly true for low-energy beams, where the noise for the GOS system can go up to a factor 2 greater than that found for CsI. The DQE of the CsI detector reaches a peak of 60%, 60%, 58%, and 50% for the RQA3, RQA5, RQA7, and RQA9 beams, respectively, whereas for the GOS screen the maximum DQE is 40%, 44%, 44%, and 35%. The contrast-detail analysis confirms that in the majority of cases the CsI scintillator is able to provide improved outcomes to those obtained with the GOS screen. CONCLUSIONS The limited diffusion of light produced by the ISS reading makes possible the achievement of very good spatial resolution. In fact, the MTF of the unit with the CsI panel is only slightly lower to that achieved with direct conversion detectors. The combination of very good spatial resolution, together with the good noise properties reached with the CsI screen, allows achieving DQE on average about 1.5 times greater than that obtained with GOS. In fact, the DQE of unit equipped with CsI is comparable to the best alternative methods available which are based on the same technology, and similar to others based on an a-Se direct conversion detectors.

Application of QC_DR Software for Acceptance Testing and Routine Quality Control of Direct Digital Radiography Systems: Initial Experiences using the Italian Association of Physicist in Medicine Quality Control Protocol

Ideally, medical x-ray imaging systems should be designed to deliver maximum image quality at an acceptable radiation risk to the patient. Quality assurance procedures are employed to ensure that these standards are maintained. A quality control protocol for direct digital radiography (DDR) systems is described and discussed. Software to automatically process and analyze the required images was developed. In this paper, the initial results obtained on equipment of different DDR manufacturers were reported. The protocol was developed to highlight even small discrepancies in standard operating performance.

Size assessment of breast lesions by means of a computer-aided detection (CAD) system for magnetic resonance mammography

PurposeThe aim of this study was to investigate the efficacy of a dedicated software tool for automated volume measurement of breast lesions in contrast-enhanced (CE) magnetic resonance mammography (MRM).Material and methodsThe size of 52 breast lesions with a known histopathological diagnosis (three benign, 49 malignant) was automatically evaluated using different techniques. The volume of all lesions was measured automatically (AVM) from CE 3D MRM examinations by means of a computer-aided detection (CAD) system and compared with the size estimates based on maximum diameter measurement (MDM) on MRM, ultrasonography (US), mammography and histopathology.ResultsCompared with histopathology as the reference method, AVM understimated lesion size by 4% on average. This result was similar to MDM (3% understimation, not significantly different) but significantly better than US and mammographic lesion measurements (24% and 33% size underestimation, respectively).ConclusionsAVM is as accurate as MDM but faster. Both methods are more accurate for size assessment of breast lesions compared with US and mammography.RiassuntoObiettivoScopo di questo studio è stato studiare le prestazioni di un software dedicato per la misura automatica del volume di lesioni identificate dalla risonanza magnetica della mammella (MRM) con utilizzo di mezzo di contrasto paramagnetico (CE).Materiali e metodiLe dimensioni di 52 lesioni mammarie con diagnosi istopatologica nota (3 benigne, 49 maligne) sono state valutate automaticamente tramite diverse tecniche. Le dimensioni delle lesioni sono state stimate automaticamente (AVM) da esami CE 3D MRM, utilizzando un sistema di computed aided diagnosis (CAD) e confrontate con stime delle dimensioni basate sulla misura del diametro massimo (MDM) in MRM, ecografia, mammografia ed anatomia patologica.RisultatiConfrontata con il reperto istopatologico come metodo di riferimento, AVM ha sottostimato la dimensione della lesione del 4% in media. Questo risultato è analogo a MDM (sottostima del 3%, differenza non significativa), ma significativamente migliore della misura della lesione ottenuta dallo studio ecografico o mammografico (sottostima del 24% e del 33% rispettivamente).ConclusioniLa valutazione dimensionale ottenuta con AVM è accurata tanto quanto MDM, ma più veloce. Entrambi i metodi ottengono nella stima della dimensione per lesioni alla mammella valori più vicini allo standard costituito dalla misura su pezzo operatorio rispetto ad ecografia e mammografia.

Patient Dose Management Solution Directly Integrated in the RIS: “Gray Detector” Software

On X-ray modalities, the information concerning the dose delivered to the patient is usually available in image headers or in structured reports stored in the picture archiving and communication system (PACS). Sometimes this information is sent in the Modality Performed Procedure Step message. By saving the information inside the Radiological Information System, it can be linked to the patient and to his/her episode/request. A software, “Gray Detector,” implementing different and complementary extraction methods was developed. Query/retrieve on images header, Modality Performed Procedure Step message analysis, or the combination of the two methods were used. In order to avoid erroneous dose-protocol association, every accession number is linked to its unique report code, allowing multiple-protocols exam recognition. The adoption of different methods to extract dosimetric information makes it possible to integrate any kind of modality in a vendor/version neutral way. Linking the dosimetric information received from a modality to the patient and to the unique report code solves, for example, common problems in computed tomography exams, where the dosimetric value related to multiple segments/studies on the modality can be associated by the technician who performs the exam only to one accession number corresponding to a single study/segment. Analyses of dosimetric indexes’ dependence on modality type, patient age, technician, and radiologist were performed. Linking dosimetric information to radiological information system data allows a contextualization of the former and helps to optimize the image-quality/dose ratio, thereby making it possible to take a clinical decision that is “patient-centered.”

A straightforward multiparametric quality control protocol for proton magnetic resonance spectroscopy: Validation and comparison of various 1.5 T and 3 T clinical scanner systems

PURPOSE The aim of this study was to propose and validate across various clinical scanner systems a straightforward multiparametric quality assurance procedure for proton magnetic resonance spectroscopy (MRS). METHODS Eighteen clinical 1.5 T and 3 T scanner systems for MRS, from 16 centres and 3 different manufacturers, were enrolled in the study. A standard spherical water phantom was employed by all centres. The acquisition protocol included 3 sets of single (isotropic) voxel (size 20 mm) PRESS acquisitions with unsuppressed water signal and acquisition voxel position at isocenter as well as off-center, repeated 4/5 times within approximately 2 months. Water peak linewidth (LW) and area under the water peak (AP) were estimated. RESULTS LW values [mean (standard deviation)] were 1.4 (1.0) Hz and 0.8 (0.3) Hz for 3 T and 1.5 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficient of variation of LW and AP for different spatial positions of acquisition voxel were 43% (20%) and 11% (11%), respectively. The mean (standard deviation) phantom T2values were 1145 (50) ms and 1010 (95) ms for 1.5 T and 3 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficients of variation for repeated measurements of LW, AP and T2 were 25% (20%), 10% (14%) and 5% (2%), respectively. CONCLUSIONS We proposed a straightforward multiparametric and not time consuming quality control protocol for MRS, which can be included in routine and periodic quality assurance procedures. The protocol has been validated and proven to be feasible in a multicentre comparison study of a fairly large number of clinical 1.5 T and 3 T scanner systems.

MODELING GLIOBLASTOMA RESPONSE TO RADIOTHERAPY BY COMBINING A TWO-COMPARTMENT KINETIC MODEL AND MULTIPARAMETRIC NMR DATA

Glioblastoma are the most common and malignant primary brain tumor, and actual treatments consist of surgery (when possible), radiotherapy and chemotherapy. Recent discoveries in biology revealed the important role of radioresistant cancer stem cell in the tumor proliferation and also showed that differentiated tumor cells can revert to a stem-like state because of radiation. These discoveries can be used to create mathematical models to study and plan new optimized radiotherapy schedules. In literature, some models have already been developed on murine population. The aim of this study was to reproduce these models, to perform a sensitivity analysis to find the most sensitive parameters and to adapt them to standard schedules used with human patients. We found that the most sensitive parameters are those involving tumor cell proliferation, radio-sensibility and quiescence times of both stem and tumor cells.