CT scans of the chest / thorax are of great importance both in the initial diagnosis and in the follow-up of pulmonary or thoracic diseases. As an example, CT angiography of the pulmonary arteries (CTPA) is worldwide considered to be gold standard test in patients with a suspicion for pulmonary embolism.

The aim of this study is to measure and compare dose efficiency of modern CT scanners for unenhanced and contrast-enhanced scan protocols of the chest/thorax. Patients who are referred for a CT of the chest/thorax will be randomly assigned to one of the three CT scanners currently in use at our institution.

Inclusion Criteria:

• patient is referred for an unenhanced CT OR contrast-enhanced CT of the chest/thorax confirmed by a board-certified radiologist ('justifying indication' according to German/European radiation protection law) AND
• patient is at least 18 years of age AND
• patient (is able to give informed consent and) has given informed consent.

Exclusion Criteria:

• high degree of medical urgency (i.e. patient cannot be consented for iv contrast according to routine procedures)
• known or suspected pregnancy, or lactating . contraindications for contrast agent (renal failure, allergy, hyperthyroidism)

We plan to share individual participant data upon request (pending final approval by the data protection officer).

Requests for sharing individual participant data will be considered at the time of publication of the first manuscript containing result data.

We plan to share data on request at this point in time.

no masking required