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A Compact X-Ray Source via Fast Microparticle Streams: A novel X-ray target concept
KTH, School of Engineering Sciences (SCI), Physics, Particle Physics, Astrophysics and Medical Imaging. KTH Royal Institute of Technology, Stockhom, Sweden. (Physics of Medical Imaging)ORCID iD: 0000-0001-6243-681X
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Sustainable development
SDG 3: Good Health and Well-Being
Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2025. , p. 52
Series
TRITA-SCI-FOU ; 2025:08
Keywords [en]
X-ray source; X-ray tube; rotating anode; microparticle target; tungsten; medical imaging; orthovolt therapy; non-destructive X-ray testing
Keywords [sv]
Röntgenkälla; röntgenrör; roterande anod; mikropartikelmål; volfram; medicinsk avbildning; ortovoltterapi; oförstörande röntgenprovning
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Technology
Identifiers
URN: urn:nbn:se:kth:diva-359471ISBN: 978-91-8106-197-0 (print)OAI: oai:DiVA.org:kth-359471DiVA, id: diva2:1934082
Public defence
2025-03-05, Sal FD05, Roslagstullsbacken 21 (Alba Nova), SE – 106 91 Stockholm, 09:15 (English)
Opponent
Supervisors
Available from: 2025-02-03 Created: 2025-02-03 Last updated: 2025-02-17Bibliographically approved
List of papers
1. The impact of tube voltage on the erosion of rotating x‐ray anodes
Open this publication in new window or tab >>The impact of tube voltage on the erosion of rotating x‐ray anodes
2025 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 52, no 2, p. 814-825Article in journal (Refereed) Published
Abstract [en]

Background

The permitted input power density of rotating anode x-ray sources is limited by the performance of available target materials. The commonly used simplified formulas for the focal spot surface temperature ignore the tube voltage despite its variation in clinical practice. Improved modeling of electron transport and target erosion, as proposed in this work, improves the prediction of x-ray output degradation by target erosion, the absolute x-ray dose output and the quality of diagnostic imaging and orthovolt cancer therapy for a wide range of technique factors.

Purpose

Improved modeling of electronic power absorption to include volume effects and surface erosion, to improve the understanding of x-ray output degradation, enhance the reliability of x-ray tubes, and safely widen their fields of use.

Methods

We combine Monte Carlo electron transport simulations, coupled thermoelasticity finite element modelling, erosion-induced surface granularity, and the temperature dependence of thermophysical and thermomechanical target properties. A semi-empirical thermomechanical criterion is proposed to predict the target erosion. We simulate the absorbed electronic power of an eroded tungsten-rhenium target, mimicked by a flat target topped with a monolayer of spheres, and compare with a pristine target.

Results

The absorbed electronic power and with it the conversion efficiency varies with tube voltage and the state of erosion. With reference to 80 kV (100%), the absorption of a severely eroded relative to a pristine target is 105% (30 kV), 99% (100 kV), 97% (120 kV), 96% (150 kV), 93% (200 kV), 87% (250 kV), and 79% (300 kV). We show that, although the simplistic Müller–Oosterkamp model of surface heating underestimates the benefit of higher tube voltages relative to operation at 80 kV, the error is limited to below −6% for 30 kV (reduction advised) and +13% for 300 kV (input power increase permitted).

Conclusions

Correcting the x-ray conversion efficiency of eroded target material, that is typically not accessible by measuring the tube current, may imply corrections to existing x-ray dose calculations. The relative increase of the allowable anode input power of rotating anode x-ray tubes with increasing tube voltage is substantially smaller than predicted by volume heating models that only rely on the focal spot surface temperature. The widely used voltage agnostic Müller–Oosterkamp formalism fails to predict the tube voltage dependency of the surface temperature of rotating anode targets, ignores the temperature dependency of the thermal diffusivity of tungsten-rhenium, and the granularity of the material. Nevertheless, we show theoretically why, backed by experience, the practical use of the Müller–Oosterkamp formalism is justified in medical imaging and provides a basis for comparison with new microparticle based targets. The reason for this surprising finding is that voltage dependent material erosion must be primarily considered as a precursor of thermal runaway effects.

Place, publisher, year, edition, pages
Wiley, 2025
Keywords
X-ray source; X-ray tube; spectral imaging; microparticle target; monochromatic X-rays; rotating anode; tungsten; medical imaging; non-destructive X-ray testing; rotating anode; tungsten; medical imaging; non-destructive X-ray testing
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-359464 (URN)10.1002/mp.17528 (DOI)001393245200001 ()2-s2.0-85209748497 (Scopus ID)
Note

QC 20250203

Available from: 2025-02-03 Created: 2025-02-03 Last updated: 2025-02-03Bibliographically approved
2. Nearly Monochromatic Bremsstrahlung of High Intensity via Microparticle Targets: A Novel Concept
Open this publication in new window or tab >>Nearly Monochromatic Bremsstrahlung of High Intensity via Microparticle Targets: A Novel Concept
2024 (English)In: Instruments, E-ISSN 2410-390X, Vol. 8, no 3, article id 42Article in journal (Refereed) Published
Abstract [en]

As an alternative to rigid anodes, a novel concept of X-ray targets consisting of a stream or a multitude of streams of fast tungsten microparticles has recently been proposed. Low-density microparticle streams resemble thin targets with nearly constant intensity distribution over a wide range of photon energies, abruptly terminating at the Duane–Hunt limit of maximum photon energy instead of falling off smoothly. According to our simulations, fast microparticles outperform classical rigid targets and enable extremely high electronic input power density and X-ray output. This opens new possibilities for generating high-intensity, nearly monochromatic X-rays. Such keV-type X-ray sources could replace expensive electron synchrotrons in appropriate applications. Furthermore, for sufficiently thin microparticle streams, the output X-ray spectra are functions of particle size, allowing modulation of the mean photon energy. We simulated the spectral response of tungsten microparticles using Monte Carlo methods and confirmed the validity of our new concept to generate near-monochrome spectra and high intensity with microparticle-based X-ray sources, outperforming classical X-ray tubes. Furthermore, we confirm a weak size dependence of the mean energies of filtered X-rays. We complement previous results highlighting the advantages of microparticle-based X-ray targets and aim at the implementation of the new concept in the future.

Place, publisher, year, edition, pages
MDPI AG, 2024
Keywords
X-ray source, X-ray tube, spectral imaging, microparticle target, monochromatic X-rays, rotating anode, tungsten, medical imaging, non-destructive X-ray testing, rotating anode, tungsten, medical imaging, non-destructive X-ray testing
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-359460 (URN)10.3390/instruments8030042 (DOI)2-s2.0-85205059356 (Scopus ID)
Note

QC 20250203

Available from: 2025-02-03 Created: 2025-02-03 Last updated: 2025-02-03Bibliographically approved
3. Microparticle Hybrid Target Simulation for keV X-ray Sources
Open this publication in new window or tab >>Microparticle Hybrid Target Simulation for keV X-ray Sources
Show others...
2024 (English)In: Instruments, E-ISSN 2410-390X, Vol. 8, no 2, article id 32Article in journal (Refereed) Published
Abstract [en]

The spatiotemporal resolution of diagnostic X-ray images obtained with rotating-anode X-ray tubes has remained limited as the development of rigid, high-performance target materials has slowed down. However, novel imaging techniques using finer detector pixels and orthovolt cancer therapy employing narrow X-ray focal spots demand improved output from brilliant keV X-ray sources. Since its advent in 1929, rotating-anode technology has become the greatest bottleneck to improvement. To overcome this limitation, the current authors have devised a novel X-ray generation technology based on tungsten microparticle targets. The current study investigated a hybrid solution of a stream of fast tungsten microparticles and a rotating anode to both harvest the benefits of the improved performance of the new solution and to reuse known technology. The rotating anode captures energy that may pass a partially opaque microparticle stream and thereby contributes to X-ray generation. With reference to fast-rotating anodes and a highly appreciated small focal spot of a standardized size of 0.3 for an 8° target angle (physical: 0.45 mm × 4.67 mm), we calculated a potential output gain of at least 85% for non-melting microparticles and of 124% if melting is envisioned. Microparticle charging can be remediated by electron backscattering and electron field emission. The adoption of such a solution enables substantially improved image resolution.

Place, publisher, year, edition, pages
Multidisciplinary Digital Publishing Institute (MDPI), 2024
Keywords
medical imaging, microparticle target, non-destructive X-ray testing, orthovolt therapy, rotating anode, tungsten, X-ray source, X-ray tube
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-349930 (URN)10.3390/instruments8020032 (DOI)2-s2.0-85196869412 (Scopus ID)
Note

QC 20240704

Available from: 2024-07-03 Created: 2024-07-03 Last updated: 2025-02-03Bibliographically approved
4. A compact X-ray source via fast microparticle streams
Open this publication in new window or tab >>A compact X-ray source via fast microparticle streams
Show others...
2024 (English)In: Communications Engineering, E-ISSN 2731-3395, Vol. 3, no 1, article id 171Article in journal (Refereed) Published
Abstract [en]

The spatiotemporal resolution of diagnostic X-ray images is limited by the erosion and rupture of conventional stationary and rotating anodes of X-ray tubes from extreme density of input power and thermal cycling of the anode material. Conversely, detector technology has developed rapidly. Finer detector pixels demand improved output from brilliant keV-type X-ray sources with smaller X-ray focal spots than today and would be available to improve the efficacy of medical imaging. In addition, novel cancer therapy demands for greatly improved output from X-ray sources. However, since its advent in 1929, the technology of high-output compact X-ray tubes has relied upon focused electrons hitting a spinning rigid rotating anode; a technology that, despite of substantial investment in material technology, has become the primary bottleneck of further improvement. In the current study, an alternative target concept employing a stream of fast discrete metallic microparticles that intersect with the electron beam is explored by simulations that cover the most critical uncertainties. The concept is expected to have far-reaching impact in diagnostic imaging, radiation cancer therapy and non-destructive testing. We outline technical implementations that may become the basis of future X-ray source developments based on the suggested paradigm shift.

Place, publisher, year, edition, pages
Springer Nature, 2024
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-356975 (URN)10.1038/s44172-024-00323-z (DOI)2-s2.0-85209408695 (Scopus ID)
Note

QC 20241128

Available from: 2024-11-28 Created: 2024-11-28 Last updated: 2025-02-03Bibliographically approved

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