III.B.45.   The most appropriate instrument for measuring the scattered x-ray exposure from a patient is a:

    a.   Geiger counter.

    b.   Large ionization chamber.    Correct.

    c.   Small ionization chamber.

    d.   Scintillation detector.

    Discussion:   The scattered radiation from a patient during an x-ray procedure produces relatively low exposure which would require a large ionization chamber to measure it.   Small ionization chambers are less sensitive and would be appropriate for measurements in the direct x-ray beam.   A Geiger counter would detect the scattered radiation but does not provide an accurate measurement.

    Reference:   Physical Principles of Medical Imaging, 2nd. Edition.   p. 622