The Log Graph of Reference Levels.
We suggest the use o chart that brings together all the reference doses for plain X-rays (all "standard radiographs" for all "standard patients") as an instant and global evaluator ( Fig. 1 ). Reference levels [3,
4] and good-practce levels [4,5] are taken from authorised resources.
Reference doses are based on old data but still in use.
Good practice in the years 1990-1995 was significantly better than reference levels (doses were lowered with 10% - 60% -see Fig. 1 ).
New improvements are expected in the last years as new equipments are spreading (the digital era).
We present the use of that chart in the evaluation of some real practices.
Case 1: Old Equipment / Good practice
- Old biphasic generator (100 Hz)
- Additional filtering was used
- Sensitive screens (400 DIN)
- Removable anti-scatter grid used only when necessary
- High-KV techniques used
The recorded doses ( Fig. 1 ) are very low showing that screen sensitivity and good practice are more important than equipment "age" (for comparison see Case 2).
Case 2: HF Generator / Low sensitivity screens
- High frequency generator
- Low sensitivity (200 DIN) screens
The recorded doses ( Fig. 6 ) are all higher than good-practice values and some are even higher that reference levels.
Comparing with Case 1 (Low frequency generator but 400 DIN screens) we prove once more that screens are more important than the X-Ray generator!
Assume now that we will change screens with 400 DIN ones (halving the doses)...
As depicted on the chart ( Fig. 6 ),
the doses for some of the radiographs would still remain above the reference levels.
The identified causes were:
- the anti-scatter grid was not removable and free-cassette technique was not used when appropriate (pelvis and chest for babies and children,
chest for slim adult)
- low KV techniques were used
- no additional filter was used
Case 3: Direct Digital - No Low-Dose Guarantee!
- Brand-new direct digital unit
- Solid-state detector
- Removable anti-scatter grids
- Automatic additional filtering
Globally,
very low doses ( Fig. 7 ),
but there are some cases with too high doses.
Identified causes:
- Anti-scatter grid present when not necessary (forgotten in place)
- Plaster or prosthetic material partially covering the AEC detector cells
Case 4: Phosphor plates (PSP) - Over-exposed images are NOT Black !!!
- HF generator
- Photostimulable Phosphor Plates (PSP)
Unexpected high doses ( Fig. 7 ).
Causes under evaluation:
- Automatic Exposure Control (AEC) not calibrated,
not used or cells used incorrectly.