CHEST, MEDIASTINAL VESSELS
| Preparatory steps: | |||
| - | Indications: suspected or known major vessel aneurysm, dissection or congenital anomaly | ||
| - | Advisable preliminary investigations: chest radiography, including lateral projection; MRI or transoesophageal ultrasonography may be alternative examinations without exposure to ionising radiation | ||
| - | Patient preparation: information about the procedure; restraint from food, but not fluid, is recommended, if intravenous contrast media are to be given | ||
| - | Scan projection radiograph: frontal from neck to upper abdomen | ||
| 1. | DIAGNOSTIC REQUIREMENTS | ||
| Image criteria: | |||
| 1.1 | Visualization of | ||
| 1.1.1 | Entire thoracic aorta | ||
| 1.1.2 | Entire vena cava | ||
| 1.1.3 | Entire heart | ||
| 1.1.4 | Vessels after intravenous contrast media | ||
| 1.2 | Critical reproduction | ||
| 1.2.1 | Visually sharp reproduction of the contour of the thoracic aorta | ||
| 1.2.2 | Visually sharp reproduction of the wall of the thoracic aorta | ||
| 1.2.3 | Visually sharp reproduction of the superior vena cava | ||
| 1.2.4 | Visually sharp reproduction of the major anterior mediastinal vessels | ||
| 1.2.5 | Visually sharp reproduction of the heart | ||
| 1.2.6 | Visually sharp reproduction of the inferior vena cava | ||
| 1.2.7 | Visually sharp reproduction of large and medium sized pulmonary vessels | ||
| 2. | CRITERIA FOR RADIATION DOSE TO THE PATIENT | ||
| 2.1 | CTDIW | : | no specific value as yet available (for information: routine chest: 30 mGy) |
| 2.1 | DLP | : | no specific value as yet available (for information: routine chest: 650 mGy cm) |
| 3. | EXAMPLES OF GOOD IMAGING TECHNIQUE | ||
| 3.1 | Patient position | : | supine, arms above the head |
| 3.2 | Volume of investigation | : | may be limited to area of radiographic abnormality or clinically suspected lesion |
| 3.3 | Nominal slice thickness | : | 4-5 mm serial or preferably helical |
| 3.4 | Inter-slice distance/pitch | : | contiguous or a pitch = 1.0; 2-4 mm or a pitch up to 1.2 - 1.5 for large lesions |
| 3.5 | FOV | : | limited to area of the heart and major vessels |
| 3.6 | Gantry tilt | : | none |
| 3.7 | X-ray tube voltage (kV) | : | standard |
| 3.8 | Tube current and exposure time product (mAs) | : | should be as low as consistent with required image quality |
| 3.9 | Reconstruction algorithm | : | soft tissue/standard |
| 3.10 | Window width | : | 100-400 HU (soft tissue, unenhanced examination) 150-500 HU (soft tissue, enhanced examination) |
| 3.11 | Window level | : | 0-50 HU (soft tissue, unenhanced examination) 20-150 HU (soft tissue, enhanced examination, depends on dose and method of contrast administration) |
| 4. | CLINICAL CONDITIONS WITH IMPACT ON GOOD IMAGING PERFORMANCE | ||
| 4.1 | Motion | - | movement artefact deteriorates the image quality. This is prevented by a standard breath-hold technique; alternatively if this is not possible scan during quiet respiration |
| 4.2 | Intravenous contrast media | - | enhancement is required for many examinations |
| 4.3 | Problems and pitfalls | - | artefact from the cardiac outline may cross the aorta and mimic dissection flap |
| - | inhomogeneities in luminal opacification due to inconstant blood flow | ||
| - | inappropriate administration of contrast media may mimic thrombus | ||
| 4.4 | Modification to technique | - | not usually required |