Large-format high-performance CCD sensor for medical x-ray applications

Medical Imaging 2005: Physics of Medical Imaging

Altunbaş

et al. 2005

We are constructing and investigating a Scan Equalization Digital Radiography (SEDR) system using an a-Si:H based flat-panel detector. With this system, slot-scan imaging with regionally adjustable beam width is used to achieve scatter rejection and exposure equalization. As part of the SEDR system, we have developed and implemented an electronic aftcollimation technique, referred to as the Alternate Line Erasure and Readout (ALER), by modifying the electronics of an a-Si:H/a-Se based flat-panel detector to alter the sequence of image readout. Instead of reading the image line by line, the leading edge line of the scanning fan beam is reset to erase the scatter component accumulated prior to the arrival of the fan beam while the trailing edge line is read out to acquire the exposure signals integrated following the exposure of the scanning fan beam. This resetting and readout cycle is repeated and synchronized to the motion of the scanning fan beam. To guide the selection of the slot width in implementing the SEDR system, measurements of the scatter-toprimary ratio (SPR) and relative contrast-to-noise ratio (RCNR) were made and compared for various slot widths.Our preliminary testing has demonstrated that it is feasible to implement an electronic aft-collimation technique to effectively reject scattered radiation without attenuating the primary x-rays and without using a bulky, heavy aftcollimator. The SPR and RCNR measurements indicated that the performance of the slot-scan imaging technique improves with narrower slot width and is generally better than the anti-scatter grid method.

Section: Introductionmentioning

confidence: 99%

Scan equalization digital radiography (SEDR): implementation with a flat-panel detector

Medical Imaging 2005: Physics of Medical Imaging

Altunbaş

et al. 2005

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] However, only in recent years, due to advances of digital and computer technology, has the concept of totally digital and filmless radiography operation become feasible. Conventional projection x-ray imaging has relied on the use of screen/film combinations as the x-ray detector.…”

Section: Introductionmentioning

confidence: 99%

Comparison of a-Si:H/CsI flat-panel digital imaging systems with CR-and CCD-based systems: image quality measurements

Medical Imaging 2001: Physics of Medical Imaging

Rong

et al. 2001

The amorphous silicon/cesium iodide (a-Si:H/CsI:Tl) flat-panel imaging systems have recently become commercially available for both chest and mammographic imaging applications. This new detector technology is considered to be a significant improvement over CR techniques. In this work, we measured the image properties for two commercial flat-panel systems and compared them with those measured for CR and CCD based imaging systems. Image quality measurements related to detector properties such as linearity, MTF, NPS and DQE are presented and compared at selected chest and mammographic imaging techniques. Factors and issues related to these measurements are discussed. For chest imaging, the flat-panel system was found to have slightly lower MTFs but significantly higher DQEs than the CR system. For mammographic imaging, the CCD-based system was found to have the highest MTF, followed in order by the flat-panel and CR systems. The flat-panel system was found to have the highest DQEs, followed in the order by the CCD-based and CR systems. The DQEs of the flat-panel systems were found to increase with exposure while those of the CR systems decrease slightly with the exposure in both chest and mammographic imaging. The DQEs of the CCD-based system were found to vary little for exposures ranging from 1 to 30 mR.

“…Digital image acquisition and processing techniques can enhance the diagnostic image quality in stationary projection radiography and provide image data for digital image storage, transmission and display with a Picture Archiving and Communication System ͑PACS͒. Digital x-ray imaging techniques based on new detector technologies such as computed radiography ͑CR͒ or storage phosphor ͑SP͒ imaging, [1][2][3][4][5] optically-fiber-optically coupled CCDs, [6][7][8][9] photodiode arrays, 10 selenium, or cesium iodide based amorphous silicon ͑a-Si:H͒ flat-panel detectors, [11][12][13][14][15][16][17][18][19][20][21] have been developed and become commercially available. Among them, the computed radiography ͑CR͒ technique has been commercially available for over a decade and has gained acceptance in a wide range of radiographic examinations.…”

Section: Introductionmentioning

confidence: 99%

Regional improvement of signal‐to‐noise and contrast‐to‐noise ratios in dual‐screen CR chest imaging—a phantom study

2001

Medical Physics

The improvement of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in dual-screen computed radiography (CR) has been investigated for various regions in images of an anthropomorphic chest phantom. With the dual-screen CR technique, two image plates are placed in a cassette and exposed together during imaging. The exposed plates are separately scanned to form a front image and a back image, which are then registered and superimposed to form a composite image with improved SNRs and CNRs. The improvement can be optimized by applying specifically selected weighting factors during superimposition. In this study, dual-screen CR images of an anthropomorphic chest phantom were acquired and formed with four different combinations of standard resolution (ST) and high-resolution (HR) screens: ST-ST, ST-HR, HR-ST, and HR-HR. SNRs and their improvements were measured and compared over twelve representative regions-of-interest (ROIs) in these images. A 19.1%-45.7% increase of the SNR was observed, depending on the ROI and screen combination used. The optimal weighting factors were found to vary by only 4.5%-12.4%. Largest improvement was found in the lung field for all screen combinations. Improvement of CNRs was investigated over two ROIs in the lung field using the rib bones as the contrast objects and a 29.2%-43.9% improvement of the CNR was observed. Among the four screen combinations, ST-ST resulted in the most SNR and CNR improvement, followed in order by HR-ST, HR-HR, and ST-HR. The HR-ST combination yielded the lowest spatial variation of the optimal weighting factors with improved SNRs and CNRs close to those of the ST-ST combination.