[Computed tomography of the lungs. A step into the fourth dimension].
OBJECTIVE
To discuss the techniques for four dimensional computed tomography of the lungs in tumour patients.


METHODS
The image acquisition in CT can be done using respiratory gating in two different ways: the helical or cine mode. In the helical mode, the couch moves continuously during image and respiratory signal acquisition. In the cine mode, the couch remains in the same position during at least one complete respiratory cycle and then moves to next position. The 4D images are either acquired prospectively or reconstructed retrospectively with dedicated algorithms in a freely selectable respiratory phase.


RESULTS
The time information required for motion depiction in 4D imaging can be obtained with tolerable motion artefacts. Partial projection and stepladder-artifacts are occurring predominantly close to the diaphragm, where the displacement is most prominent. Due to the long exposure times, radiation exposure is significantly higher compared to a simple breathhold helical acquisition. Therefore, the use of 4D-CT is restricted to only specific indications (i.e. radiotherapy planning).


CONCLUSIONS
4D-CT of the lung allows evaluating the respiration-correlated displacement of lungs and tumours in space for radiotherapy planning.
Dinkel
J
J
Abteilung für Radiologie, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg. j.dinkel@dkfz-heidelberg.de
Hintze
C
C
Rochet
N
N
Thieke
C
C
Biederer
J
J
D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008168:Lung / Q000000981:diagnostic imaging*; D008171:Lung Diseases / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement / Q000379:methods*; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
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