Spiral CT and radiation dose H. Imhof a, *, N. Schibany a , A. Ba-Ssalamah a , C. Czerny a , A. Hojreh a , F. Kainberger a , C. Krestan a , H. Kudler b , I. No ¨ bauer a , R. Nowotny b a Department of Osteology, University Klin. f. Radiodiagnostik, Waehringer Guertel 18-20, A-1090 Vienna, Austria b Institut f. biomed. Technik und Physik, AKH-Wien, Vienna, Austria Received 23 June 2002; received in revised form 23 July 2002; accepted 25 July 2002 Abstract Recent studies in the USA and Europe state that computed tomography (CT) scans compromise only 3  /5% of all radiological exams, but they contribute 35  /45% of total radiation dose to the patient population. These studies lead to concern by several public authorities. Basis of CT-dose measurements is the computed tomography dose index (CTDI), which was established 1981. Nowadays there are several modifications of the CTDI values, which may lead to confusion. It is suggested to use the standardized CTDI  /100 w. value together with the dose length product in all CT-examinations. These values should be printed on all CT-images and allows an evaluation of the individualized patient dose. Nowadays, radiologist’s aim must be to work at the lowest maximal diagnostic acceptable signal to noise ratio. To decrease radiation dose radiologist should use low kV and mA, but high pitches. Newly developed CT-dose-reduction soft-wares and filters should be installed in all CT-machines. We should critically compare the average dose used for a specific examination with the reference dose used in this country and/or Europe. Greater differences should caution the radiologist. Finally, we as radiologists must check very carefully all indications and recommend alternative imaging methods. But we have also to teach our customers */patients and medical doctors who are non-radiologists */that a ‘good’ image is not that which show all possible information, but that which visualize ‘only’ the diagnostic necessary information. # 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Spiral CT; Radiation dose; Computed tomography dose index-value; Low-dose CT 1. Introduction Recent studies in the USA and Europe state that computed tomography (CT) scans compromise only 3  / 5% of all radiological exams, but they contribute 35  / 45% of total radiation dose to the patient population [1  / 4]. With the arrival and clinical routine use of multi-slice/ multi-detector spiral CT’s this relationship could be- come even worse. The Food and Drug Administration (FDA) in the USA writes that unnecessary radiation exposure must be avoided and significant dose reduc- tions can be achieved without change of clinical efficacy. But also the European Commission states in their 97/43 Directive its concern about the radiation dose and puts CT-examinations in the range of high-radiation dose exams [5,6]. Under these circumstances and the steady increase of CT-studies dose-aspects and imaging with spiral CT- machines should be reviewed. Moreover we want to know how much the dose can be lowered without a loss of relevant diagnostic information. 2. Methods of CT-dose measurements There are various quantities describing the radiation dose to the patient from CT-examinations. In the following the most important quantities having gained international acceptance are described. In 1981 the US FDA introduced the computed tomography dose index (CTDI) as a physical dose quantity to characterise radiation exposure delivered by CT scanners in a single-slice. The CTDI is a measure for the radiation output of the CT slice comprising the * Corresponding author. Tel.:  /43-1-40400-5803; fax:  /43-1- 40400-3777 E-mail address: mr@univie.ac.at (H. Imhof). European Journal of Radiology 47 (2003) 29 /37 www.elsevier.com/locate/ejrad 0720-048X/02/$ - see front matter # 2002 Elsevier Science Ireland Ltd. All rights reserved. PII:S0720-048X(02)00232-2