a. In angiography, the contrast material introduced into the circulatory system is
circulated so rapidly that extremely short intervals between exposures are necessary for
adequate demonstration of the vasculature. The intervals between exposures are
usually fractions of seconds; thus manual cassette changing is impossible. Biplane
digital imaging plates are used to rapidly and automatically capture the image, which
permits several radiographs to be made in a very short period of time. They are
electrically powered and synchronized with the x-ray generator so that the exposures
are automatically controlled.
b. These devices can only be used with x-ray generators specifically wired to
accept them. Most of the newer units, fixed or portable, that have a potential of at least
200 mA and 125 kVp are so wired.
c. When the biplane digital imaging plates film changer is connected to the x-ray
generator, the hand switch circuit of the generator is bypassed and, on some units, the
rotor is activated. Thus, the digital imager controls the x-ray tube and subsequent
production of x-rays.
1-10. AUTOMATIC CONTRAST MEDIUM INJECTOR
With the advent of new technologies in computerized tomography and magnetic
resonance imaging, contrast material must be injected with sufficient pressure to
overcome the patient's systemic arterial pressure and to maintain a bolus to minimize
dilution with blood. The flow rate is affected by many variables such as the viscosity of
contrast media, length and diameter of the catheter, and injection pressure. There are
many types of automatic contrast injectors, including the types pictured in figure 1-3.
Figure: 1-3. Types of automatic contrast media injectors.