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Article ; Online: Early CT physics research at Massachusetts General Hospital.

Pelc, Norbert J / Chesler, David A

2023 Volume 50 Suppl 1, Page(s) 85–90

Abstract: Although CT imaging was introduced at Massachusetts General Hospital (MGH) quite early, with its first CT scanner installed in 1973, CT research at MGH started years earlier. The goal of this paper is to describe some of this innovative work and related ... ...

Abstract	Although CT imaging was introduced at Massachusetts General Hospital (MGH) quite early, with its first CT scanner installed in 1973, CT research at MGH started years earlier. The goal of this paper is to describe some of this innovative work and related accomplishments.
MeSH term(s)	Hospitals, General ; Massachusetts ; Physics ; Tomography, X-Ray Computed
Language	English
Publishing date	2023-02-08
Publishing country	United States
Document type	Journal Article ; Review
ZDB-ID	188780-4
ISSN	2473-4209 ; 0094-2405
ISSN (online)	2473-4209
ISSN	0094-2405
DOI	10.1002/mp.16229
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Article ; Online: The effects of intra-detector Compton scatter on low-frequency DQE for photon-counting CT using edge-on-irradiated silicon detectors.

Grönberg, Fredrik / Yin, Zhye / Maltz, Jonathan S / Pelc, Norbert J / Persson, Mats

Medical physics

2024

Abstract: Background: Edge-on-irradiated silicon detectors are currently being investigated for use in full-body photon-counting computed tomography (CT) applications. The low atomic number of silicon leads to a significant number of incident photons being ... ...

Abstract	Background: Edge-on-irradiated silicon detectors are currently being investigated for use in full-body photon-counting computed tomography (CT) applications. The low atomic number of silicon leads to a significant number of incident photons being Compton scattered in the detector, depositing a part of their energy and potentially being counted multiple times. Even though the physics of Compton scatter is well established, the effects of Compton interactions in the detector on image quality for an edge-on-irradiated silicon detector have still not been thoroughly investigated. Purpose: To investigate and explain effects of Compton scatter on low-frequency detective quantum efficiency (DQE) for photon-counting CT using edge-on-irradiated silicon detectors. Methods: We extend an existing Monte Carlo model of an edge-on-irradiated silicon detector with 60 mm active absorption depth, previously used to evaluate spatial-frequency-based performance, to develop projection and image domain performance metrics for pure density and pure spectral imaging tasks with 30 and 40 cm water backgrounds. We show that the lowest energy threshold of the detector can be used as an effective discriminator of primary counts and cross-talk caused by Compton scatter. We study the developed metrics as functions of the lowest threshold energy for root-mean-square electronic noise levels of 0.8, 1.6, and 3.2 keV, where the intermediate level 1.6 keV corresponds to the noise level previously measured on a single sensor element in isolation. We also compare the performance of a modeled detector with 8, 4, and 2 optimized energy bins to a detector with 1-keV-wide bins. Results: In terms of low-frequency DQE for density imaging, there is a tradeoff between using a threshold low enough to capture Compton interactions and avoiding electronic noise counts. For 30 cm water phantom, 4 energy bins, and a root-mean-square electronic noise of 0.8, 1.6, and 3.2 keV, it is optimal to put the lowest energy threshold at 3, 6, and 1 keV, which gives optimal projection-domain DQEs of 0.64, 0.59, and 0.52, respectively. Low-frequency DQE for spectral imaging also benefits from measuring Compton interactions with respective optimal thresholds of 12, 12, and 13 keV. No large dependence on background thickness was observed. For the intermediate noise level (1.6 keV), increasing the lowest threshold from 5 to 35 keV increases the variance in a iodine basis image by 60%-62% (30 cm phantom) and 67%-69% (40 cm phantom), with 8 bins. Both spectral and density DQE are adversely affected by increasing the electronic noise level. Image-domain DQE exhibits similar qualitative behavior as projection-domain DQE. Conclusions: Compton interactions contribute significantly to the density imaging performance of edge-on-irradiated silicon detectors. With the studied detector topology, the benefit of counting primary Compton interactions outweighs the penalty of multiple counting at all lowest threshold energies. Compton interactions also contribute significantly to the spectral imaging performance for measured energies above 10 keV.
Language	English
Publishing date	2024-05-16
Publishing country	United States
Document type	Journal Article
ZDB-ID	188780-4
ISSN	2473-4209 ; 0094-2405
ISSN (online)	2473-4209
ISSN	0094-2405
DOI	10.1002/mp.17122
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Article: Spectral Photon Counting CT: Imaging Algorithms and Performance Assessment.

Wang, Adam S / Pelc, Norbert J

IEEE transactions on radiation and plasma medical sciences

2020 Volume 5, Issue 4, Page(s) 453–464

Abstract: Photon counting x-ray detectors (PCDs) with spectral capabilities have the potential to revolutionize computed tomography (CT) for medical imaging. The ideal PCD provides accurate energy information for each incident x-ray, and at high spatial resolution. ...

Abstract	Photon counting x-ray detectors (PCDs) with spectral capabilities have the potential to revolutionize computed tomography (CT) for medical imaging. The ideal PCD provides accurate energy information for each incident x-ray, and at high spatial resolution. This information enables material-specific imaging, enhanced radiation dose efficiency, and improved spatial resolution in CT images. In practice, PCDs are affected by non-idealities, including limited energy resolution, pulse pileup, and cross talk due to charge sharing, K-fluorescence, and Compton scattering. In order to maximize their performance, PCDs must be carefully designed to reduce these effects and then later account for them during correction and post-acquisition steps. This review article examines algorithms for using PCDs in spectral CT applications, including how non-idealities impact image quality. Performance assessment metrics that account for spatial resolution and noise such as the detective quantum efficiency (DQE) can be used to compare different PCD designs, as well as compare PCDs with conventional energy integrating detectors (EIDs). These methods play an important role in enhancing spectral CT images and assessing the overall performance of PCDs.
Language	English
Publishing date	2020-07-07
Publishing country	United States
Document type	Journal Article
ISSN	2469-7311
ISSN	2469-7311
DOI	10.1109/trpms.2020.3007380
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Article ; Online: Accurate Image Domain Noise Insertion in CT Images.

Divel, Sarah E / Pelc, Norbert J

IEEE transactions on medical imaging

2019 Volume 39, Issue 6, Page(s) 1906–1916

Abstract: Tools to simulate lower dose, noisy computed tomography (CT) images from existing data enable protocol optimization by quantifying the trade-off between patient dose and image quality. Many studies have developed and validated noise insertion techniques; ...

Abstract	Tools to simulate lower dose, noisy computed tomography (CT) images from existing data enable protocol optimization by quantifying the trade-off between patient dose and image quality. Many studies have developed and validated noise insertion techniques; however, most of these tools operate on proprietary projection data which can be difficult to access and can be time consuming when a large number of realizations is needed. In response, this work aims to develop and validate an image domain approach to accurately insert CT noise and simulate low dose scans. In this framework, information from the image is utilized to estimate the variance map and local noise power spectra (NPS). Normally distributed noise is filtered within small patches in the image domain using the inverse Fourier transform of the square root of the estimated local NPS to generate noise with the appropriate spatial correlation. The patches are overlapped and element-wise multiplied by the standard deviation map to produce locally varying, spatially correlated noise. The resulting noise image is scaled based on the relationship between the initial and desired dose and added to the original image. The results demonstrate excellent agreement between traditional projection domain methods and the proposed method, both for simulated and real data sets. This new framework is not intended to replace projection domain methods; rather, it fills a gap in CT noise simulation tools and is an accurate alternative when projection domain methods are not practical, for example, in large scale repeatability or detectability studies.
MeSH term(s)	Algorithms ; Computer Simulation ; Humans ; Image Processing, Computer-Assisted ; Phantoms, Imaging ; Radiation Dosage ; Tomography, X-Ray Computed
Language	English
Publishing date	2019-12-23
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	622531-7
ISSN	1558-254X ; 0278-0062
ISSN (online)	1558-254X
ISSN	0278-0062
DOI	10.1109/TMI.2019.2961837
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Article: Special Section Guest Editorial: Computed tomography (CT) at 50 years.

La Rivière, Patrick J / Fahrig, Rebecca / Pelc, Norbert J

Journal of medical imaging (Bellingham, Wash.)

2021 Volume 8, Issue 5, Page(s) 52101

Abstract: Guest editors Patrick La Riviere, Rebecca Fahrig, and Norbert Pelc introduce the JMI Special Section Celebrating X-Ray Computed Tomography at 50. ...

Abstract	Guest editors Patrick La Riviere, Rebecca Fahrig, and Norbert Pelc introduce the JMI Special Section Celebrating X-Ray Computed Tomography at 50.
Language	English
Publishing date	2021-10-29
Publishing country	United States
Document type	Journal Article
ISSN	2329-4302
ISSN	2329-4302
DOI	10.1117/1.JMI.8.5.052101
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Article: How CT happened: the early development of medical computed tomography.

Schulz, Raymond A / Stein, Jay A / Pelc, Norbert J

Journal of medical imaging (Bellingham, Wash.)

2021 Volume 8, Issue 5, Page(s) 52110

Abstract: As we arrive at the 50th anniversary of the first computed tomography (CT) scan of a live patient, we take this opportunity to revisit the history of early CT development. It is not an exaggeration to say that the invention of CT may represent the ... ...

Abstract	As we arrive at the 50th anniversary of the first computed tomography (CT) scan of a live patient, we take this opportunity to revisit the history of early CT development. It is not an exaggeration to say that the invention of CT may represent the greatest revolution in medical imaging since the discovery of x-rays. We cover events over a period of about two decades that started with the realization that accurate cross-sectional soft-tissue detail is possible and could be a significant advance. We describe in some detail the development of the first CT system and then the rapid technical advances during the following years that included the entry of many companies into the field and the circumstances that led many of those entrants to exit the field. Rather than focusing on the specific technical details (which can be found elsewhere), we include stories and events in the hope that broader lessons can be learned. As the first x-ray-based digital imaging modality, CT brought into common use an exceptional tool that benefits countless patients every day. It also introduced dramatic changes to biomedical imaging as a field that continues to influence progress to this day.
Language	English
Publishing date	2021-10-29
Publishing country	United States
Document type	Journal Article
ISSN	2329-4302
ISSN	2329-4302
DOI	10.1117/1.JMI.8.5.052110
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Article ; Online: Empirical optimization of energy bin weights for compressing measurements with realistic photon counting x-ray detectors.

Yang, Yirong / Wang, Sen / Pal, Debashish / Yin, Zhye / Pelc, Norbert J / Wang, Adam S

Medical physics

2023 Volume 51, Issue 1, Page(s) 224–238

Abstract: Background: Photon counting detectors (PCDs) provide higher spatial resolution, improved contrast-to-noise ratio (CNR), and energy discriminating capabilities. However, the greatly increased amount of projection data in photon counting computed ... ...

Abstract	Background: Photon counting detectors (PCDs) provide higher spatial resolution, improved contrast-to-noise ratio (CNR), and energy discriminating capabilities. However, the greatly increased amount of projection data in photon counting computed tomography (PCCT) systems becomes challenging to transmit through the slip ring, process, and store. Purpose: This study proposes and evaluates an empirical optimization algorithm to obtain optimal energy weights for energy bin data compression. This algorithm is universally applicable to spectral imaging tasks including 2 and 3 material decomposition (MD) tasks and virtual monoenergetic images (VMIs). This method is simple to implement while preserving spectral information for the full range of object thicknesses and is applicable to different PCDs, for example, silicon detectors and CdTe detectors. Methods: We used realistic detector energy response models to simulate the spectral response of different PCDs and an empirical calibration method to fit a semi-empirical forward model for each PCD. We numerically optimized the optimal energy weights by minimizing the average relative Cramér-Rao lower bound (CRLB) due to the energy-weighted bin compression, for MD and VMI tasks over a range of material area density Results: The results show that for 2 MD, the energy bin compression method can reduce PCCT data size by 75% and 60%, with an average variance penalty of less than 17% and 3% for silicon and CdTe detectors, respectively. For 3 MD tasks with a K-edge material (iodine), this method can reduce the data size by 62.5% and 40% with an average variance penalty of less than 12% and 13% for silicon and CdTe detectors, respectively. Conclusions: We proposed an energy bin compression method that is broadly applicable to different PCCT systems and object sizes, with high data compression ratio and little loss of spectral information.
MeSH term(s)	X-Rays ; Cadmium Compounds ; Silicon ; Tellurium ; Quantum Dots ; Photons ; Phantoms, Imaging
Chemical Substances	cadmium telluride (STG188WO13) ; Cadmium Compounds ; Silicon (Z4152N8IUI) ; Tellurium (NQA0O090ZJ)
Language	English
Publishing date	2023-07-03
Publishing country	United States
Document type	Journal Article
ZDB-ID	188780-4
ISSN	2473-4209 ; 0094-2405
ISSN (online)	2473-4209
ISSN	0094-2405
DOI	10.1002/mp.16590
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Article ; Online: Recent and future directions in CT imaging.

Pelc, Norbert J

Annals of biomedical engineering

2014 Volume 42, Issue 2, Page(s) 260–268

Abstract: Computed tomography (CT) has made enormous technical advances since its introduction into clinical use. The engineering improvements have in turn led to important clinical applications and large impact in patient care. This paper reviews the technology ... ...

Abstract	Computed tomography (CT) has made enormous technical advances since its introduction into clinical use. The engineering improvements have in turn led to important clinical applications and large impact in patient care. This paper reviews the technology development trends in CT since its introduction and uses these trends to help illuminate likely future progress. The prediction is that significant further improvements in speed, spatial resolution and dose efficiency can be expected in the next decade.
MeSH term(s)	Humans ; Tomography, X-Ray Computed/methods ; Tomography, X-Ray Computed/trends
Language	English
Publishing date	2014-01-17
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't ; Review
ZDB-ID	185984-5
ISSN	1573-9686 ; 0191-5649 ; 0090-6964
ISSN (online)	1573-9686
ISSN	0191-5649 ; 0090-6964
DOI	10.1007/s10439-014-0974-z
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Article: Detective quantum efficiency of photon-counting CdTe and Si detectors for computed tomography: a simulation study.

Persson, Mats / Wang, Adam / Pelc, Norbert J

Journal of medical imaging (Bellingham, Wash.)

2020 Volume 7, Issue 4, Page(s) 43501

Abstract: Purpose: ...

Abstract	Purpose:
Language	English
Publishing date	2020-07-17
Publishing country	United States
Document type	Journal Article
ISSN	2329-4302
ISSN	2329-4302
DOI	10.1117/1.JMI.7.4.043501
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Article ; Online: Detective efficiency of photon counting detectors with spectral degradation and crosstalk.

Rajbhandary, Paurakh L / Persson, Mats / Pelc, Norbert J

Medical physics

2019 Volume 47, Issue 1, Page(s) 27–36

Abstract: Purpose: Charge sharing and migration of scattered and fluorescence photons in an energy discriminating photon counting detector (PCD) degrade the detector's energy response and can cause a single incident photon to be registered as multiple events at ... ...

Abstract	Purpose: Charge sharing and migration of scattered and fluorescence photons in an energy discriminating photon counting detector (PCD) degrade the detector's energy response and can cause a single incident photon to be registered as multiple events at different energies among neighboring pixels, leading to spatio-energetic correlation. Such a correlation in conventional linear, space-invariant imaging system can be usefully characterized by the frequency dependent detective quantum efficiency DQE(f). Defining and estimating DQE(f) for PCDs in a manner consistent with that of conventional detectors is complicated because the traditional definition of DQE(f) does not address spectral information. Methods: We introduce the concept of presampling spectroscopic detective quantum efficiency, DQE Results: Zero frequency DQE Conclusions: Our results show that spatio-energetic correlations degrade DQE
MeSH term(s)	Models, Theoretical ; Photons ; Radiation Monitoring/methods ; Scattering, Radiation
Language	English
Publishing date	2019-11-22
Publishing country	United States
Document type	Journal Article
ZDB-ID	188780-4
ISSN	2473-4209 ; 0094-2405
ISSN (online)	2473-4209
ISSN	0094-2405
DOI	10.1002/mp.13889
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