Compensator models for fluence field modulated computed tomography

Bartolac, Steven; Jaffray, David A.

doi:10.1118/1.4829513

Cited by 21 publications

(28 citation statements)

References 51 publications

(70 reference statements)

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“…Recently, there has been a lot interest within the CT imaging community concerning fluence field modulation (Kolditz et al 2010, Heuscher & Noo 2011, Heuscher & Noo 2012, Bartolac et al 2010, Bartolac et al 2011, Bartolac & Jaffray 2012, Chen et al 2011, Stiller et al 2012, Sperl et al 2010, Burion et al 2011, Hsieh & Pelc 2013 a , Hsieh & Pelc 2013 b ). The ability to modulate the incident x-ray fluence in CT imaging has been proposed to implement volume of interest imaging (VOI) (Bartolac et al 2010, Bartolac et al 2011, Bartolac & Jaffray 2012, Kolditz et al 2010, Heuscher & Noo 2011, Heuscher & Noo 2012, Chen et al 2011), improve standard CT imaging (Stiller et al 2012, Sperl et al 2010, Burion et al 2011, Hsieh & Pelc 2013 a , Hsieh & Pelc 2013 b ), and may be a necessary technology if photon counting CT is to overcome detector saturation and charge trapping problems (McCollough et al 2012, Shikhaliev 2009).…”

Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

“…The ability to modulate the incident x-ray fluence in CT imaging has been proposed to implement volume of interest imaging (VOI) (Bartolac et al 2010, Bartolac et al 2011, Bartolac & Jaffray 2012, Kolditz et al 2010, Heuscher & Noo 2011, Heuscher & Noo 2012, Chen et al 2011), improve standard CT imaging (Stiller et al 2012, Sperl et al 2010, Burion et al 2011, Hsieh & Pelc 2013 a , Hsieh & Pelc 2013 b ), and may be a necessary technology if photon counting CT is to overcome detector saturation and charge trapping problems (McCollough et al 2012, Shikhaliev 2009). …”

Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

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Experimental realization of fluence field modulated CT using digital beam attenuation

Szczykutowicz¹,

Mistretta²

2014

Phys. Med. Biol.

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Purpose Tailoring CT scan acquisition parameters to individual patients is a topic of much research in the CT imaging community. It is now common place to find automatically adjusted tube current options for modern CT scanners. In addition, the use of beam shaping filters, commonly called bowtie filters, is available on most CT systems and allows for different body regions to receive different incident x-ray fluence distributions. However, no method currently exists which allows for the form of the incident x-ray fluence distribution to change as a function of view angle. This study represents the first experimental realization of fluence field modulated CT (FFMCT) for a c-arm geometry CT scan. Methods: X-ray fluence modulation is accomplished using a digital beam attenuator (DBA). The device is composed of 10 iron wedge pairs that modulate the thickness of iron x-rays must traverse before reaching a patient. Using this device, experimental data was taken using a Siemens Zeego c-arm scanner. Scans were performed on a cylindrical polyethylene phantom and on two different sections of an anthropomorphic phantom. The DBA was used to equalize the x-ray fluence striking the detector for each scan. Non DBA, or “flat field” scans were also acquired of the same phantom objects for comparison. In addition, a scan was performed in which the DBA was used to enable volume of interest (VOI) imaging. In VOI, only a small sub-volume within a patient receives full dose and the rest of the patient receives a much lower dose. Data corrections unique to using a piece-wise constant modulator were also developed. Results The feasibility of FFMCT implemented using a DBA device has been demonstrated. Initial results suggest dose reductions of up to 3.6 times relative to “flat field” CT. In addition to dose reduction, the DBA enables a large improvement in image noise uniformity and the ability to provide regionally enhanced signal to noise using VOI imaging techniques. Conclusions The results presented in this paper take the field of FFMCT from the theoretical stage to that of possible clinical implementation. FFMCT, as shown in this paper, can reduce patient dose while maintaining or improving image quality. In addition, the DBA has been experimentally shown to be well suited to implement entirely new imaging methods like photon counting and VOI imaging.

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Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

Experimental realization of fluence field modulated CT using digital beam attenuation

Szczykutowicz¹,

Mistretta²

2014

Phys. Med. Biol.

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“…TV-based ones, can also be used. We also noticed that there is current research on fluence field modulation in CBCT, which has the potential to yield a CBCT image of a prescribed spatially varying image quality while using only the minimally necessary amount of radiation exposure to the patient (Bartolac et al , 2011; Szczykutowicz and Mistretta, 2014; Bartolac, 2014; Graham et al , 2007). However, currently it is still challenging to achieve this in practice due to hardware limitations.…”

Section: Discussionmentioning

confidence: 97%

Reconstructing cone-beam CT with spatially varying qualities for adaptive radiotherapy: a proof-of-principle study

Yan

et al. 2014

Phys. Med. Biol.

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With the aim of maximally reducing imaging dose while meeting requirements for adaptive radiation therapy (ART), we propose in this paper a new cone beam CT (CBCT) acquisition and reconstruction method that delivers images with a low noise level inside a region of interest (ROI) and a relatively high noise level outside the ROI. The acquired projection images include two groups: densely sampled projections at a low exposure with a large field of view (FOV) and sparsely sampled projections at a high exposure with a small FOV corresponding to the ROI. A new algorithm combining the conventional filtered back-projection algorithm and the tight-frame iterative reconstruction algorithm is also designed to reconstruct the CBCT based on these projection data. We have validated our method on a simulated head-and-neck (HN) patient case, a semi-real experiment conducted on a HN cancer patient under a full-fan scan mode, as well as a Catphan phantom under a half-fan scan mode. Relative root-mean-square errors (RRMSE) of less than 3% for the entire image and ~1% within the ROI compared to the ground truth have been observed. These numbers demonstrate the ability of our proposed method to reconstruct high-quality images inside the ROI. As for the part outside ROI, although the images are relatively noisy, it can still provide sufficient information for radiation dose calculations in ART. Dose distributions calculated on our CBCT image and on a standard CBCT image are in agreement, with a mean relative difference of 0.082% inside the ROI and 0.038% outside the ROI. Compared with the standard clinical CBCT scheme, an imaging dose reduction of approximately 3–6 times inside the ROI was achieved, as well as an 8 times outside the ROI. Regarding computational efficiency, it takes 1–3 min to reconstruct a CBCT image depending on the number of projections used. These results indicate that the proposed method has the potential for application in ART.

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“…4 It can be expected that an even further dose and scatter reduction could be achieved if a compensator could adjust its FM in real time. Work in this area has already begun and promising results have been demonstrated by Sperl et al 5 and Bartolac et al [6][7][8] In the present study, we are considering CT images that will be read by clinicians for general use; therefore, image quality must be maintained over the entire imaging FOV. This differs from the FFMCT work of Bartolac et al [6][7][8] and Heuscher and Noo 9,10 in which subregions inside the FOV were defined and signal-to-ratio (SNR) was boosted inside these regions and lowered outside allowing for an overall dose savings for the patient.…”

Section: Introductionmentioning

confidence: 99%

“…Our work is more similar to the work of Sperl et al 5 in this regard. However, the work of Bartolac et al [6][7][8] was purely simulation based and our proposed FM method could theoretically be used to implement their methods experimentally.…”

Section: Introductionmentioning

confidence: 99%

Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

Szczykutowicz

Mistretta

2013

Med. Phys.

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Purpose: The purpose of this work is to introduce a new device that allows for patient-specific imaging-dose modulation in conventional and cone-beam CT. The device is called a digital beam attenuator (DBA). The DBA modulates an x-ray beam by varying the attenuation of a set of attenuating wedge filters across the fan angle. The ability to modulate the imaging dose across the fan beam represents another stride in the direction of personalized medicine. With the DBA, imaging dose can be tailored for a given patient anatomy, or even tailored to provide signal-to-noise ratio enhancement within a region of interest. This modulation enables decreases in: dose, scatter, detector dynamic range requirements, and noise nonuniformities. In addition to introducing the DBA, the simulation framework used to study the DBA under different configurations is presented. Finally, a detailed study on the choice of the material used to build the DBA is presented. Methods: To change the attenuator thickness, the authors propose to use an overlapping wedge design. In this design, for each wedge pair, one wedge is held stationary and another wedge is moved over the stationary wedge. The composite thickness of the two wedges changes as a function of the amount of overlap between the wedges. To validate the DBA concept and study design changes, a simulation environment was constructed. The environment allows for changes to system geometry, different source spectra, DBA wedge design modifications, and supports both voxelized and analytic phantom models. A study of all the elements from atomic number 1 to 92 were evaluated for use as DBA filter material. The amount of dynamic range and tube loading for each element were calculated for various DBA designs. Tube loading was calculated by comparing the attenuation of the DBA at its minimum attenuation position to a filtered non-DBA acquisition. Results: The design and parametrization of DBA implemented FFMCT has been introduced. A simulation framework was presented with which DBA-FFMCT, bowtie filter CT acquisitions, and unmodulated CT acquisitions can be simulated. The study on wedge filter design concluded that the ideal filter material should have an atomic number in the range of 21-34. Iron was chosen for an experimental relative-tube-loading measurement and showed that DBA-FFMCT scans could be acquired with negligible increases in tube power demands. Conclusions: The basic idea of DBA implemented fluence field modulated CT, a simulation framework to verify the concept, and a filter selection study have been presented. The use of a DBA represents another step toward the ultimate in patient specific CT dose delivery as patient dose can be delivered uniquely as a function of view and fan angle using this device.

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Compensator models for fluence field modulated computed tomography

Cited by 21 publications

References 51 publications

Experimental realization of fluence field modulated CT using digital beam attenuation

Experimental realization of fluence field modulated CT using digital beam attenuation

Reconstructing cone-beam CT with spatially varying qualities for adaptive radiotherapy: a proof-of-principle study

Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

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