Temporal artifacts in flat dynamic x-ray detectors

Overdick, Michael; Solf, Torsten; Wischmann, H.‐A.

doi:10.1117/12.430913

Cited by 42 publications

(39 citation statements)

References 7 publications

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“…108 Previous reports have studied image lag by measuring the residual signal in the dark field, lasting in the order of minutes following beam off. 89,89,93,136,136,140,140 The extent of the image lag has been found to be highly dependent on the number of frames read out, or acquired, as opposed to an explicit dependence on the time of irradiation. Therefore one would expect a change in the influence of ghosting on the response for alternative or irregular frame acquisition rates.…”

Section: Introductionmentioning

confidence: 99%

On Radiotherapy Dose Verification With a Flat-Panel Imager

McDermott¹

2009

Radiotherapy and Oncology

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Section: Introductionmentioning

confidence: 99%

On Radiotherapy Dose Verification With a Flat-Panel Imager

McDermott¹

2009

Radiotherapy and Oncology

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“…[10][11][12] Recently, several methods for measuring temporal modulation transfer function (MTF) and detective quantum efficiency (DQE) have been proposed and the properties of FPDs used in dynamic imaging have been reported. [13][14][15] However, there have been no studies regarding how image lag and ghosting affect motion tracking by dynamic imaging with FPDs. In external radiotherapy, there is concern regarding the relationship between image quality and total patient dose during real-time tumor tracking, because it is necessary to optimize imaging parameters in each patient to keep patient dose as low as possible while maintaining tracking accuracy.…”

Section: Introductionmentioning

confidence: 99%

Effects of image lag on real-time target tracking in radiotherapy

Tanaka

Ichikawa

Mori³

et al. 2010

SPIE Proceedings

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There is a concern that image lag may reduce accuracy of real-time target tracking in radiotherapy. This study was performed to investigate influence of image lag on the accuracy of target tracking in radiotherapy. Fluoroscopic images were obtained using a direct type of dynamic flat-panel detector (FPD) system under conditions of target tracking during radiotherapy. The images continued to be read out after X-irradiations and cutoff, and image lag properties in the system were then determined. Subsequently, a tungsten materials plate with a precision edge was mounted on to a motor control device, which provided a constant velocity. The plate was moved into the center of the detector at movement rate of 10 and 20 mm/s, covering lung tumor movement of normal breathing, and MTF and profile curves were measured on the edges covering and uncovering the detector. A lung tumor with blurred edge due to image lag was simulated using the results and then superimposed on breathing chest radiographs of a patient. The moving target with and without image lag was traced using a template-matching technique. In the results, the target could be traced within a margin for error in external radiotherapy. The results indicated that there was no effect of image lag on target tracking in usual breathing speed in a radiotherapy situation. Further studies are required to investigate influence by the other factors, such as exposure dose, target size and shape, imaging rate, and thickness of a patient's body.

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“…[1][2][3][4][5][6][7] Detector lag is defined as signal present in frames following the frame in which it was generated. In fluoroscopy, lag causes temporal blurring.…”

Section: Introductionmentioning

confidence: 99%

A forward bias method for lag correction of an a-Si flat panel detector

et al. 2011

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Purpose: Digital a-Si flat panel (FP) x-ray detectors can exhibit detector lag, or residual signal, of several percent that can cause ghosting in projection images or severe shading artifacts, known as the radar artifact, in cone-beam computed tomography (CBCT) reconstructions. A major contributor to detector lag is believed to be defect states, or traps, in the a-Si layer of the FP. Software methods to characterize and correct for the detector lag exist, but they may make assumptions such as system linearity and time invariance, which may not be true. The purpose of this work is to investigate a new hardware based method to reduce lag in an a-Si FP and to evaluate its effectiveness at removing shading artifacts in CBCT reconstructions. The feasibility of a novel, partially hardware based solution is also examined. Methods: The proposed hardware solution for lag reduction requires only a minor change to the FP. For pulsed irradiation, the proposed method inserts a new operation step between the readout and data collection stages. During this new stage the photodiode is operated in a forward bias mode, which fills the defect states with charge. A Varian 4030CB panel was modified to allow for operation in the forward bias mode. The contrast of residual lag ghosts was measured for lag frames 2 and 100 after irradiation ceased for standard and forward bias modes. Detector step response, lag, SNR, modulation transfer function (MTF), and detective quantum efficiency (DQE) measurements were made with standard and forward bias firmware. CBCT data of pelvic and head phantoms were also collected. Results: Overall, the 2nd and 100th detector lag frame residual signals were reduced 70%-88% using the new method. SNR, MTF, and DQE measurements show a small decrease in collected signal and a small increase in noise. The forward bias hardware successfully reduced the radar artifact in the CBCT reconstruction of the pelvic and head phantoms by 48%-81%. Conclusions: Overall, the forward bias method has been found to greatly reduce detector lag ghosts in projection data and the radar artifact in CBCT reconstructions. The method is limited to improvements of the a-Si photodiode response only. A future hybrid mode may overcome any limitations of this method.

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Temporal artifacts in flat dynamic x-ray detectors

Cited by 42 publications

References 7 publications

On Radiotherapy Dose Verification With a Flat-Panel Imager

On Radiotherapy Dose Verification With a Flat-Panel Imager

Effects of image lag on real-time target tracking in radiotherapy

A forward bias method for lag correction of an a-Si flat panel detector

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