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Radiology and CT

An important area for a medical physicist is the optimization of the radiation dose and image quality. The challenge is to establish sufficient image quality for a specific diagnostic task with the lowest effective dose to the patient. Within radiology, the use of computed tomography (CT) has greatly increased in recent years. CT is associated with higher radiation doses than other radiation-based medical examinations such as plain radiography and most nuclear medicine examinations. Radiation dose from a general CT examination of the thorax is approximately five times the natural background radiation a person is exposed to in a year. Consequently it is of great importance to minimize radiation doses.

The continuous technological developments in new CT hardware and software have received remarkable interest in the past years. The aim is to optimise image quality and radiation dose to the patient. These developments require close collaboration between medical physicists, radiologists, radiographers and manufacturers in order to be effectively and optimally used. Our research focus on implementation and evaluation of technical approaches to the optimisation of CT:

  • Evaluation of automatic exposure control in CT to achieve a desired level of image quality and to reduce radiation dose1 (Figure 1).

Tube current modulation along the longitudinal axis of a chest phantom
Figure 1. Tube current modulation along the longitudinal axis of a chest phantom. The modulation is performed according to the phantoms size, shape and attenuation to ensure optimal image quality and minimal radiation dose.

 

  • Evaluation of iterative CT reconstruction for image quality improvements and dose reduction2, 3 (Figure 2).

Comparison
Figure 2. Comparison between the conventional analytical reconstruction method filtered back-projection (FBP) and the iterative reconstruction (IR) method. Using IR the image noise is decreased and there is potential to lower the radiation dose.

  • Evaluation of iterative algorithms for metal artifact reduction in CT (Figure 3).

Iterative algorithm
Figure 3. Iterative algorithm for metal artifact reduction allows artifacts caused by a hip implant to be reduced significantly.

  • Evaluation of clinical applications for dual energy CT4, such as virtual non-contrast-enhanced images5, virtual monochromatic images, and material composition of various tissues6 (Figure 4).

 

The basic principle of dual energy
Figure 4. The basic principle of dual energy CT is material decomposition based on attenuation differences at different energy levels. The technique allows evaluation of different images, e.g. monochromatic, virtual non-contrast, iodine map and effective

  • Evaluation of CT pelvimetry in terms of foetal radiation dose and measurement accuracy7.
  • Evaluation of amount of intravenous contrast medium in relation to radiation dose8, 9.

 

References

1.      Automatic exposure control in computed tomography - an evaluation of systems from different manufacturers. Söderberg M, Gunnarsson M. Acta Radiologica. Apr 30, 625-634, (2010).

2.      Six iterative reconstruction algorithms in brain CT: a phantom study on image quality at different radiation dose levels. Löve A, Olsson ML, Siemund R, Stålhammar F, Björkman-Burtscher IM, Söderberg M. Br J Radiol, 86(1031), (2013).

3.      Evaluation of an iterative model-based reconstruction of pediatric abdominal CT with regard to image quality and radiation dose. Aurumskjöld ML, Söderberg M, Tingberg A, Ydström K. Acta Radiologica. Jun 59, 740-747, (2017).

4.      Evaluation of image quality and radiation dose of abdominal dual-energy CT. Schmidt D, Söderberg M, Nilsson M, Lindvall H, Christoffersen C, Leander P. Acta Radiologica. Jul 59, 845-852, (2018).

5.      Reliability of virtual non-contrast computed tomography angiography: comparing it with the real deal. Lehti L, Söderberg M, Höglund P, Nyman U, Gottsäter A, Wassélius J. Acta Radiol Open. Aug 20, 1-6, (2018).

6.      Material decomposition in dual-energy computed tomography separates high-Z elements from iodine, identifying potential contrast media tailored for dual contrast medium examinations. Fält T, Söderberg M, Wasselius J, Leander P. J Comput Assist Tomogr. Nov-Dec 39, 975-980, (2015).

7.      Estimation of foetal radiation dose in a comparative study of pelvimetry with conventional radiography and different computer tomography methods. Phexell E, Söderberg M, Bolejko A.  International Journal of Radiology & Radiation Therapy. 5(4), 243-247, (2018).

8.      Seesaw balancing radiation dose and i.v. contrast dose: evaluation of a new abdominal CT protocol for reducing age-specific risk. Fält T, Söderberg M, Hörberg L, Carlgren I, Leander P. AJR Am J Roentgenol. Feb 200(2), 383-388, (2013).

9.      Impact of iterative reconstructions on image noise and low-contrast object detection in low kVp simulated abdominal CT: a phantom study. Holmquist F, Nyman U, Siemund R, Geijer M, Söderberg M. Acta Radiologica. Sep 57, 1079-1088, (2015).

INFORMATION

Project leader

Anders Tingberg, PhD
anders [dot] tingberg [at] med [dot] lu [dot] se
+46 40 33 11 55

Mikael Gunnarsson, PhD
mikael [dot] gunnarsson [at] med [dot] lu [dot] se
+46 40 33 86 79

Marcus Söderberg, PhD
marcus [dot] soderber [at] med [dot] lu [dot] se
+46 40 33 86 51


Veronica Fransson, PhD student
veronica [dot] fransson [at] med [dot] lu [dot] se