Although SCTs require collimation
, they need it less frequently than Newtonians do.
The setup of S1-S2 includes a collimation
lens with focal length [f.sub.C] = 700 mm and diameter [d.sub.C] = 90 mm.
Five of the eight cases that scored 0 were acquired at 5 mm or 2.5 mm collimation
. Two cases (patients 14 and 20) were scored 0 because they involved perineural spread of tumor along the second and third divisions of the trigeminal nerve, so that complete extent of tumor was not well demonstrated.
The evaluation was based on x-ray beam collimation
observed on radiographs stored in the film library of the hospitals, questionnaires administered to radiographers and light beam misalignment test conducted on the x-ray machines.
Pitch is the distance the table travels per rotation divided by the beam collimation
. Dose varies inversely with pitch.
The scan was performed during 10-second breath hold, with a 0.6 mm collimation
, 0.6 mm slice thickness reconstruction.
Here is another view regarding the lack of a lead glove and collimation
in the radiograph of a toddler's hand originally published in the Technical Query column and discussed in the May/June Open Forum (see Figure): While tight collimation
and lead gloves are both important for radiation safety and protection, anyone who has taken many hand radiographs of toddlers knows it can be a very difficult procedure!
Mechanical or optical x-ray beam collimation
in conjunction with video camera alignment allows confirmation of specific analysis areas/ features.
Other problems have included improper collimation
, no purging and incorrect zero diopter settings and infinity focus.