Technique
Although each manufacturer has different protocols, the basic techniques are similar. No patient preparation is required. Blood samples do not have to be obtained, and no contrast material is used. Some manufacturers recommend the removal of any metal object that may be near the chest region. Examples include metal buttons, bras with underwires, and necklaces. Metal objects are removed because they cause non-linear x-ray scatter that can produce artifacts in the images.
Asking patients to practice holding their breath may be helpful, not because a long breath hold is needed (usual duration, 15-30 s), but because reproducibility of their breath-holding is enhanced. Many centers ask the patient to complete a risk-assessment questionnaire to aid in the overall interpretation of the study. The patient lies supine on the scanner gantry with the arms over the head. If the patient cannot raise the arms, an acceptable scan can be obtained with the patient's arms at his or her sides.
Settings for the scanner depend on the manufacturer's recommendations. A typical protocol for a quad-slice multidetector CT would be 165 ma, 120 kVp, 0.5 pitch, and quad X 2.5 mm.
The use of cardiac gating is an area of current disagreement. Some manufacturers do not use it at all, while others disagree about whether it should be used prospectively or retrospectively. Although the addition of gating is not difficult, it requires more patient preparation than that of the simple CT scanning. Leads must be placed on the patient's chest; at some centers, the patient may need to wear a hospital gown.
Asking patients to practice holding their breath may be helpful, not because a long breath hold is needed (usual duration, 15-30 s), but because reproducibility of their breath-holding is enhanced. Many centers ask the patient to complete a risk-assessment questionnaire to aid in the overall interpretation of the study. The patient lies supine on the scanner gantry with the arms over the head. If the patient cannot raise the arms, an acceptable scan can be obtained with the patient's arms at his or her sides.
Settings for the scanner depend on the manufacturer's recommendations. A typical protocol for a quad-slice multidetector CT would be 165 ma, 120 kVp, 0.5 pitch, and quad X 2.5 mm.
The use of cardiac gating is an area of current disagreement. Some manufacturers do not use it at all, while others disagree about whether it should be used prospectively or retrospectively. Although the addition of gating is not difficult, it requires more patient preparation than that of the simple CT scanning. Leads must be placed on the patient's chest; at some centers, the patient may need to wear a hospital gown.
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