1. RAD 254 Chapter 16 Image Quality Film factors Geometric factors Subject factors

2. Radiographic Quality Resolution = ability to image two or more objects and distinguish them on the radiograph –Spatial resolution = imaging small objects with high subject contrast that are close together (breast micro calcifications in breast tissue) –Contrast resolution = ability to distinguish items with similar subject contrast (white-gray matter) –Related terms: detail; recorded detail; visibility of detail

3. “Noise” Film graininess, structure mottle, quantum mottle, scatter Film graininess = distribution, size, space of silver halide in the emulsion (mammo) Structure mottle = as above, but involves the intensifying screen crystals (mammo) Quantum mottle = random way x-ray photons interact with film/receptor (increased speed receptor= higher QM) Scatter

4. Quantum mottle reduction High mAs Lowest optimum kVp’s Slowest possible film (receptor) screen speeds

5. Film factors Characteristic curve : density, contrast, speed latitude –Relationship of OD and radiation exposure –Also called H & D curve, Hortchkof curve, sensitometric curve, –Terms: base + fog, toe, average gradient/straight line portion, shoulder, solarized portion Processing: Time, temperature

6. Sensitometry/densitometry Sensitometry = exposing the film to radiation or light in step form exposures Densitometry = measuring the amount of light transmitted through each exposed step –Plotting the optical density (OD) verses “log relative exposure” (LRE) = the curve –Increments in LRE of.3 = double the exposure –Useful range of OD is.2 – 2.5

7. Contrast Film/image receptor contrast (inherent in the film-screen combination) – reflected in the ave. gradient portion of the H & D curve (more vertical curve = higher contrast) Subject contrast: size, shape and attenuating characteristics of the body part imaged

8. Film Characteristics Speed = sensitivity and responsiveness of the emulsion of the film to x-rays/light Latitude = range of exposures to create blackness –“wider” latitude (responds more slowly to light/x-rays) = lower contrast. –Latitude and contrast are INVERSLY PROPORTIONAL

9. Geometric factors Distortion –Depends on object thickness, position, shape Magnification –To minimize magnification: use long SID and short OID Blur (focal spot blur) – caused by the effective focal spot – larger on the cathode end of the emission spectrum

10. Subject Factors Contrast : thickness, tissue mass density, atomic number of tissue being imaged –Can be somewhat modified by varied kVp’s Motion

11. Primary factors kVp = primary control of radiographic contrast mAs = primary control of optical density (OD)

12. Four Patient Factors Four Image-quality Factors Three Types of Technique Charts Three Types of AEC’s

13. Patient Factors Body habitus : –Sthenic – “average sized patient” –Hyposthenic – thin but healthy –Hypersthenic – big “frame” usually overweight –Asthenic – small, frail, emaciated, usually elderly Thickness of part Body composition Pathology

14. Body Composition Atomic mass density of body parts to be imaged –Wide range of atomic mass densities = higher kVp’s to be used (CXR) Pathology – radiolucent (destructive) or radiopaque (additive)

15. Radiolucent – Destructive Pathology Active TB Atrophy Bowel obstruction Cancer (for the most part destructive) Degenerative arthritis Emphysema Osteoporosis Pnuemothorax

16. Radiopaque – Additive/constructive Aortic aneurysm Ascites (abnormal accum. Intraperitoneal fluid) Atelectasis (collapse of alveoli) Cirrhosis Hypertrophy Metastases (for the most part) Pleural effusion Pneumonia Sclerosis (hardening of tissue)

17. Image quality factors Optical Density – primarily controlled by mAs (20-30% change to see any difference) and SID Contrast – shades of gray – primarily controlled by kVp (hi/low; long/short scale) Image Detail – visibility of detail (contrast resolution) and sharpness of detail (spatial resolution) Distortion – improper alignment of part

18. Technique Charts Variable kVp – increasing kVp’s with increased body part thickness Fixed kVp – (Arthur Fuch’s) highest OPTIMUM kVp – atomic mass density driven High kVp – over 100 kVp – barium studies and CXR’s

19. Automatic Exposure Control Usually 3 sensors –Sensors shut off x-rays when a pre-set amount of OD is achieved (pre-set kVp’s) 600 mAs over-ride (if sensors do NOT shut off x-rays, the machine automatically terminates the exposure at 600 mAs) – some units have variable “back up timers” for this

20. Anatomically Programmed Radiography Microprocessor technology based upon anatomical area to be imaged –Uses anatomic illustrations for the tech to select the anatomical part to be imaged and the unit does the mA, kV and AEC selection