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Application- and patient size-dependent optimization of x-ray spectra for CT

Kalender, Willi A. ; Deak, Paul ; Kellermeier, Markus ; van Straten, Marcel ; Vollmar, Sabrina V.

Medical physics (Lancaster), 2009-03, Vol.36 (3), p.993-1007 [Periódico revisado por pares]

United States: American Association of Physicists in Medicine

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Título:
Application- and patient size-dependent optimization of x-ray spectra for CT
Autor: Kalender, Willi A. ; Deak, Paul ; Kellermeier, Markus ; van Straten, Marcel ; Vollmar, Sabrina V.
Assuntos: ABDOMEN ; Adult ; Angiography ; anthropometry ; biological tissues ; BIOMEDICAL RADIOGRAPHY ; Biophysical Phenomena ; Body Size ; bone ; Calcium ; calcium compounds ; CALCIUM PHOSPHATES ; cardiology ; CHEST ; Computed tomography ; Computer Simulation ; computerised tomography ; COMPUTERIZED TOMOGRAPHY ; contrast‐to‐noise ratio ; CORONARIES ; dose ; Dose‐volume analysis ; dosimetry ; Durapatite ; Electric measurements ; Heart - diagnostic imaging ; Humans ; Image quality ; image scanners ; IODINE ; Medical image contrast ; Medical image noise ; Medical image quality ; Medical imaging ; Medical X‐ray imaging ; Monte Carlo Method ; optimisation ; OPTIMIZATION ; paediatrics ; PHANTOMS ; Phantoms, Imaging ; RADIATION DOSE DISTRIBUTIONS ; RADIATION DOSES ; Radiography, Abdominal - methods ; Radiography, Abdominal - statistics & numerical data ; Radiography, Thoracic - methods ; Radiography, Thoracic - statistics & numerical data ; RADIOLOGY AND NUCLEAR MEDICINE ; REDUCTION ; simulations ; SKELETON ; Tomography, X-Ray Computed - methods ; Tomography, X-Ray Computed - statistics & numerical data ; Water ; X-RAY SPECTRA
É parte de: Medical physics (Lancaster), 2009-03, Vol.36 (3), p.993-1007
Notas: willi.kalender@imp.uni-erlangen.de
Author to whom correspondence should be addressed. Electronic addresses
Present address: Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands.
and
willi@imp.uni-erlangen.de
Telephone: +49‐9131‐8522310; Fax: +49‐9131‐8522824.
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Descrição: Although x-ray computed tomography (CT) has been in clinical use for over 3 decades, spectral optimization has not been a topic of great concern; high voltages around 120 kV have been in use since the beginning of CT. It is the purpose of this study to analyze, in a rigorous manner, the energies at which the patient dose necessary to provide a given contrast-to-noise ratio (CNR) for various diagnostic tasks can be minimized. The authors used cylindrical water phantoms and quasianthropomorphic phantoms of the thorax and the abdomen with inserts of 13 mm diameter mimicking soft tissue, bone, and iodine for simulations and measurements. To provide clearly defined contrasts, these inserts were made of solid water with a 1% difference in density (DD) to represent an energy-independent soft-tissue contrast of 10 Hounsfield units (HU), calcium hydroxyapatite (Ca) representing bone, and iodine (I) representing the typical contrast medium. To evaluate CT of the thorax, an adult thorax phantom ( 300 × 200 mm 2 ) plus extension rings up to a size of 460 × 300 mm 2 to mimic different patient cross sections were used. For CT of the abdomen, we used a phantom of 360 × 200 mm 2 and an extension ring of 460 × 300 mm 2 . The CT scanner that the authors used was a SOMATOM Definition (Siemens Healthcare, Forchheim, Germany) at 80, 100, 120, and 140 kV. Further voltage settings of 60, 75, 90, and 105 kV were available in an experimental mode. The authors determined contrast for the density difference, calcium, and iodine, and noise and 3D dose distributions for the available voltages by measurements. Additional voltage values and monoenergetic sources were evaluated by simulations. The dose-weighted contrast-to-noise ratio (CNRD) was used as the parameter for optimization. Simulations and measurements were in good agreement with respect to absolute values and trends regarding the dependence on energy for the parameters investigated. For soft-tissue imaging, the standard settings of 120–140 kV were found as adequate choices with optimal values increasing for larger cross sections, e.g., for large abdomens voltages higher than 140 kV may be indicated. For bone and iodine imaging the optimum values were generally found at significantly lower voltages of typically below 80 kV. This offers a potential for dose reduction of up to 50%, but demands significantly higher power values in most cases. The authors concluded that voltage settings in CT should be varied more often than is common in practice today and should be chosen not only according to patient size but also according to the substance imaged in order to minimize dose while not compromising image quality. A reduction from 120 to 80 kV, for example, would yield a reduction in patient dose by more than half for coronary CT angiography. The use of lower voltages has to be recommended for contrast medium studies in cardiac and pediatric CT.
Editor: United States: American Association of Physicists in Medicine
Idioma: Inglês

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Application- and patient size-dependent optimization of x-ray spectra for CT

Kalender, Willi A. ; Deak, Paul ; Kellermeier, Markus ; van Straten, Marcel ; Vollmar, Sabrina V.

United States: American Association of Physicists in Medicine

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