ACR Electronics L-32 FIELD MARKER LIGHTING SYSTEM Informações Técnicas descarregar pdf (Página 12)

devices have been developed to expedite this. Hendee and

Rossi, for example,

employ a

plastic

cylinder for

measuring SID (Reference #3).

Localization of the focal

spots on tubes should be performed as part of acceptance

testing of newly installed x-ray tubes. A repeat of this

measurement usually is not necessary until the x-ray tube

is replaced.

i-5-B. Mobile/Portable Unit

For (non-dental) mobile or portable x-ray units the

minimum x-ray source-to-skin

distance (SSD) shall be no

less than 12" (30 cm) (Reference #1).

This can be

measured directly with a

tape

measure provided the

location of the focal spot is known.

I-6. Radiation Beam Restrictors and Light Localizers

This section describes

the

evaluation of

collimators.

These devices restrict the x-ray beam and

normally use a light source

and mirror arrangement to

indicate the direction and extent of the x-ray field.

The following parameters need to be evaluated:

(a) Congruence (alignment and size) of x-ray

and light localization fields.

(b) Alignment of the central ray and the center

of the image receptor.

indication and the actual x-ray field size.

(d) Agreement of x-ray field size and image

receptor size on units equipped with

Positive Beam Limiting (PBL) collimators.

I-6-A-c. X-ray/Light Field Congruence, X-ray Field/Image

Receptor Centering, and Numerical Indicator

Accuracy

The first three collimator parameters listed in

Section I-6 (a-c) can be evaluated at the table using two

radiographs.

Align the x-ray tube assembly to the center

of the table or wall cassette holder at an

SID that is clinically used. Most units

are equipped with a light mounted on the x-ray

tube support assembly to indicate when the

radiation field is centered.

Center a 35 x 43 cm (14 x 17") cassette with

film in the cassette holder.

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