Evolution of spatial resolution in breast CT at UC Davis

Gazi, Peymon; Yang, Kai; Burkett, George W.; Aminololama-Shakeri, Shadi; Seibert, J. Anthony; Boone, John M.

doi:10.1118/1.4915079

Cited by 50 publications

(77 citation statements)

References 25 publications

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“…showed that the low electronic noise of CMOS detectors enables improved angular sampling by lowering the required dose per frame. In breast CBCT, Gazi et al . and Shen et al .…”

Section: Introductionmentioning

confidence: 99%

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

et al. 2017

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Purpose: Quantitative assessment of trabecular bone microarchitecture in extremity cone-beam CT (CBCT) would benefit from the high spatial resolution, low electronic noise, and fast scan time provided by complementary metal-oxide semiconductor (CMOS) x-ray detectors. We investigate the performance of CMOS sensors in extremity CBCT, in particular with respect to potential advantages of thin (<0.7 mm) scintillators offering higher spatial resolution. Methods: A cascaded systems model of a CMOS x-ray detector incorporating the effects of CsI:Tl scintillator thickness was developed. Simulation studies were performed using nominal extremity CBCT acquisition protocols (90 kVp, 0.126 mAs/projection). A range of scintillator thickness (0.35-0.75 mm), pixel size (0.05-0.4 mm), focal spot size (0.05-0.7 mm), magnification (1.1-2.1), and dose (15-40 mGy) was considered. The detectability index was evaluated for both CMOS and aSi:H flat-panel detector (FPD) configurations for a range of imaging tasks emphasizing spatial frequencies associated with feature size a obj . Experimental validation was performed on a CBCT test bench in the geometry of a compact orthopedic CBCT system (SAD = 43.1 cm, SDD = 56.0 cm, matching that of the Carestream OnSight 3D system). The test-bench studies involved a 0.3 mm focal spot x-ray source and two CMOS detectors (Dalsa Xineos-3030HR, 0.099 mm pixel pitch) -one with the standard CsI:Tl thickness of 0.7 mm (C700) and one with a custom 0.4 mm thick scintillator (C400). Measurements of modulation transfer function (MTF), detective quantum efficiency (DQE), and CBCT scans of a cadaveric knee (15 mGy) were obtained for each detector. Results: Optimal detectability for high-frequency tasks (feature size of~0.06 mm, consistent with the size of trabeculae) was~49 for the C700 CMOS detector compared to the a-Si:H FPD at nominal system geometry of extremity CBCT. This is due to~59 lower electronic noise of a CMOS sensor, which enables input quantum-limited imaging at smaller pixel size. Optimal pixel size for high-frequency tasks was <0.1 mm for a CMOS, compared to~0.14 mm for an a-Si:H FPD. For this fine pixel pitch, detectability of fine features could be improved by using a thinner scintillator to reduce light spread blur. A 22% increase in detectability of 0.06 mm features was found for the C400 configuration compared to C700. An improvement in the frequency at 50% modulation (f 50 ) of MTF was measured, increasing from 1.8 lp/mm for C700 to 2.5 lp/mm for C400. The C400 configuration also achieved equivalent or better DQE as C700 for frequencies above~2 mm À1. Images of cadaver specimens confirmed improved visualization of trabeculae with the C400 sensor. Conclusions: The small pixel size of CMOS detectors yields improved performance in high-resolution extremity CBCT compared to a-Si:H FPDs, particularly when coupled with a custom 0.4 mm thick scintillator. The results indicate that adoption of a CMOS detector in extremity CBCT can benefit applications in quantitative imaging of trabecular microstr...

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“…showed that the low electronic noise of CMOS detectors enables improved angular sampling by lowering the required dose per frame. In breast CBCT, Gazi et al . and Shen et al .…”

Section: Introductionmentioning

confidence: 99%

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

et al. 2017

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“…A critical requirement for a breast cancer diagnostic device is the ability to accurately detect micro‐calcification as they are frequently associated with malignancy . To date, many efforts have been exerted to optimize the detector performance of CBBCT system for better detection of micro‐calcifications, but there have not been any studies to investigate the dependency of OFR. The results presented in this study show that the OFR has a significant impact on the image quality in terms of spatial resolution and contrast, and this effect is especially prominent for fine structures (i.e., micro‐calcifications) in CBBCT images.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

et al. 2017

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Purpose: Dedicated cone beam breast CT (CBBCT) suffers from x-ray scatter contamination. We aim to identify the source of the significant difference between the scatter distributions estimated by two recent methods proposed by our group and to investigate its effect on CBBCT image quality. Method: We recently proposed two novel methods of scatter correction for CBBCT, using a library based (LB) technique and a forward projection (FP) model. Despite similar enhancement on CBBCT image qualities, these two methods obtain very different scatter distributions. We hypothesize that the off-focus radiation (OFR) is the contributor and results in nontrivial signals in x-ray projections, which is ignored in the scatter estimation via the LB method. Experiments using a thin wire test tool are designed to study the effect of OFR on CBBCT spatial resolution by measuring the point spread function (PSF) and the modulation transfer function (MTF). A narrow collimator setting is used to suppress the OFR-induced signals. In addition, "PSFs" and "MTFs" are measured on clinical CBBCT images obtained by the LB and FP methods using small calcifications as point sources. The improvement of spatial resolution achieved by suppressing OFR in the wire experiment as well as in the clinical study is quantified by the improvement ratios of PSFs and spatial frequencies at different MTF values. Our hypothesis that OFR causes the imaging difference between the FP and LB methods is verified if these ratios obtained from experimental and clinical data are consistent. Results: In the wire experiment, the results show that suppression of OFR increases the maximum signal of the PSF by about 14% and reduces the full-width-at-half-maximum (FWHM) by about 12.0%. Similar improvement on spatial resolution is achieved by the FP method compared with the LB method in the patient study. The improvement ratios of spatial frequencies at different MTF values without OFR match very well in both studies at a level of around 16%, with an average rootmean-square difference of 0.47%. Conclusion:The results of the wire experiment and the clinical study indicate that the main difference between the LB and FP methods is whether the OFR-induced signals are included after scatter correction. Our study further shows that OFR significantly affects the image spatial resolution of CBBCT, indicating that the visualization of micro-calcifications is susceptible to OFR contamination. Our finding is therefore important in further improvement of diagnostic performance of CBBCT.

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“…For low input kVp’s, Lα 2 , Lβ 4 and Lγ 1 were easily differentiated, while Kα 2 , Kα 1 and Kβ 1 were differentiated for higher kVp values (80–130 kVp). Pulsed x-ray sources have shown a valuable spatial resolution improvement in breast imaging with cone beam CTs [42]. We can expect that the pulsed emission mode, when synchronized with the digital detectors in cone beam CTs and digital tomosynthesis imaging modalities, will likely improve the spatial resolution, reduce the scattering, and reduce the radiation dose levels.…”

Section: Discussionmentioning

confidence: 99%

Characterization of continuous and pulsed emission modes of a hybrid micro focus x-ray source for medical imaging applications

Ghani

Wong

Ren

et al. 2017

Nuclear Instruments and Methods in Physics Research Section A:

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The aim of this study was to quantitatively characterize a micro focus x-ray tube that can operate in both continuous and pulsed emission modes. The micro focus x-ray source (Model L9181-06, Hamamatsu Photonics, Japan) has a varying focal spot size ranging from 16–50 μm as the source output power changes from 10–39 W. We measured the source output, beam quality, focal spot sizes, kV accuracy, spectra shapes and spatial resolution. Source output was measured using an ionization chamber for various tube voltages (kVs) with varying current (μA) and distances. The beam quality was measured in terms of half value layer (HVL), kV accuracy was measured with a non-invasive kV meter, and the spectra was measured using a compact integrated spectrometer system. The focal spot sizes were measured using a slit method with a CCD detector with a pixel pitch of 22 μm. The spatial resolution was quantitatively measured using the slit method with a CMOS flat panel detector with a 50 μm pixel pitch, and compared to the qualitative results obtained by imaging a contrast bar pattern. The focal spot sizes in the vertical direction were smaller than that of the horizontal direction, the impact of which was visible when comparing the spatial resolution values. Our analyses revealed that both emission modes yield comparable imaging performances in terms of beam quality, spectra shape and spatial resolution effects. There were no significantly large differences, thus providing the motivation for future studies to design and develop stable and robust cone beam imaging systems for various diagnostic applications.

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Evolution of spatial resolution in breast CT at UC Davis

Cited by 50 publications

References 25 publications

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

Characterization of continuous and pulsed emission modes of a hybrid micro focus x-ray source for medical imaging applications

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