SELECTIVE FILTRATION: EFFECT ON PATIENT DOSE AND RADIOGRAPHIC QUALITY

Journal Article · Sat Sep 01 04:00:00 EDT 1962 · X-Ray Technician

OSTI ID:4142319

Irvin, R

The use of added filtration to control selectively the patient radiation dose and radiographic quality is considered. Insertion of a filter between the tube port and the patient removes much soft, unwanted radiation that would have been absorbed or scattered within the patient. It is shown that filtration of x- ray photons having reduced penetrating quality affects the shape of the generated beam wave form, as demonstrated radiographically with a high-speed spin top. The film density trace for one half-cycle impulse will become progressively shorter as filtration is added. An equalizing of density from the ends to the trace center will be apparent for large values of filtration. Slight variations in over-all trace density indicate that the beam composition becomes more nearly homogeneous in character. The radiographic effect of filtration is less pronounced for heavier parts because of increased patient absorption. It is proposed that image latitude can be extended greatly at an intermediate kilovoltage by using a 1-mm copper filter. A chest radiograph taken at 85 kvp will appear to have the latitude of one exposed at 120 kvp. The use of 1 mm of copper at 85 kv requires a density correction of 6-fold masec, and at 120 kv produces radiographs of accentuated wide latitude resembling those obtained in the Mev supervoltage range (and requires doubling the ma-sec to maintain the original density). It is not practical to use 1 mm of copper below 120 kv as density compensation becomes drastic and tube loading is approached. Relevant dose data were obtained by measuring the dose at depth in a phantom of tissue density (a pressed-wood phantom with 2 r and 200 mr ionization chambers). Comparison of depth dose curves for several values of filtration revealed the reduction of integral dose by the additional copper filtration. For example, without copper but with 3.5-mm aluminum filtration the ratio of the air to mid- plane (15-cm depth) was 8; with 0.5 mm copper it was reduced to approximates 4. Studies on colon barium series showed that the visual qualities of radiographs obtained with these values of filtration are diagnostically adequate. Reduction of radiation at ovarian depth was significant. (BBB)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-18-005162
• OSTI ID: 4142319
• Journal Information: X-Ray Technician, Journal Name: X-Ray Technician Vol. Vol: 34
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ALUMINUM
BARIUM COMPOUNDS
BEAMS
BIOLOGY AND MEDICINE
COPPER
DENSITY
DIAGNOSIS
DISTRIBUTION
ENERGY
FILTERS
GONADS
INTESTINE
IONIZATION CHAMBERS
MAN
MOCKUP
OVARIES
PHOTONS
RADIATION DOSES
RADIOGRAPHY
SEX
SPIN
THICKNESS
TISSUES
TUBES
VARIATIONS
WOOD
X RADIATION