Table 2.

The literature reviewed and a summary of the exposure adaptation systems described.

Author/Paper	System	Study Design	Description	Limitations
Simon13	1. ‘Disc system’	Description of the system(s)	1. A system composed of concentric discs used to adjust exposure. Disc 1: Line up the parameters for an optimal exposure: tube current (mA), exposure time (s), tube potential (kVp), weight (lb). Turn the weight wheel to the desired weight and a set of optimal exposure parameters will be provided. If a certain kVp, mA or time is desired, turning the corresponding wheel will lead to compensation through adjustment of another factor. Disc 2: Same control as disc 1. The factors addressed are tube unit, grid, film/screen and tissue thickness combined into a density correction (DC) factor, SID (inches), kVp, mA and time. The mA and time adjustment based on linear logarithmic relationship with thickness. The kV scale based on the Bierman and Boldingh formula: (kV)5 × mAs = constant.	1. None stated in article.
		2. Finding kilovolt peak (kVp)	2. The radiographer needs to multiply the DC value (which includes anatomy thickness) by 2 then add 40 to find the kVp required for the anatomy being examined.	2. None stated in article.
Gyss14	1. Optimum kilovoltage technique	Description of the system(s)	1. All factors including kVp are fixed except time. Optimum time is found for an average patient. For a thicker than average patient, the time is doubled and for a thinner than average patient it is halved.	None stated in article.
	2. Variable kilovoltage technique		2. The kVp is adjusted ‘to compensate … for part thickness … [and] radiopacity of the part.’ (p. 76) To adjust exposure for extremities that are imaged with a screen the kVp is adjusted 2 kVp per cm and without screen kVp is adjusted 3 kVp per cm. To adjust exposure because of radiopacity the patients are divided into three categories; hard to penetrate, normal and easy to penetrate. Hard to penetrate needs the addition of 4 kVp to the normal technique and easy to penetrate requires the subtraction of 4 kVp.	2. ‘Radiographs of any given part will vary in contrast’. (p. 76)
Power15	1. Half value layer (HVL)	Description of the system(s)	1. An ‘increase in thickness of body tissue of 3 cm. requires DOUBLE the exposure to achieve the same amount of film blackening’. (p. 16) [sic]	1. None stated in article.
		2. 25% rule		2. Every cm increase of patient thickness requires a 25% increase in milliampere-seconds (mAs).	2. None stated in article.
Lyons16	Optimum kilovoltage technique	Description of the system(s)	All factors including kVp are fixed except time. Optimum time is found for an average patient. For a thicker than average patient the time is doubled and for a thinner than average patient it is halved.	None stated in article.
Pinson17	Unit step radiography	Description of the system(s)	Involves the use of a calliper which has been modified to have a scale of ‘units’ oppose to a centimetre scale. The values of the exposure parameters are also assigned ‘units’. Measure the anatomy to be imaged with this calliper and the ‘units’ is read. The correct exposure is when the sum of the ‘units’ of the set of exposure parameters matches the ‘units’ read off the calliper.	‘The greatest error will occur when the calliper measurement is midway between a whole number and the next half unit’. (p. 9)
McDaniel18	HVL	Water Bath Study Radiographs made each time there was an increase in 4 cm of water. Then for every 3.5 cm increase. Consistency of image density was observed when the exposure (time) was double in response to each increase.	For every 4 cm increase in patient thickness requires a doubling of exposure (time) in order to achieve an image of equal density. The study found slight density fluctuations when doubling exposure for every 4 cm increase in thickness and found more consistent density occurs when doubling exposure for every 3.5 cm increase in thickness.	The more accurate value for HVL is between 3.3 cm and 3.8 cm but the use of 4 cm has a negligible effect and is suitable for practical use.
Funke19	1. Pegged kilovoltage technique	Description of the system(s)	1. The kVps 44, 51, 57, 65, 75, 86, 100 and 120 are the only ones required for most radiologic examinations. Each step in this sequence delivers twice the exposure to the film than the preceding step. For each part of anatomy, set of one these values as optimum and only adjust mAs in response to an increase in patient thickness.	1. Beyond certain limits it becomes impractical to increase the milliampere-seconds further because the limits of safe tube loading or acceptable exposure times cannot be exceeded. Thus, a change in kVp is required which alters the contrast of the image.
			2. HVL		2. ‘The milliampere seconds should be doubled (or reduced by one half) for every three centimetres of tissue thickness’. (p. 207) [sic]	2. This method fails when the anatomy thickness is greater than 30 cm, particular with high kVp and a HVL of 4 cm should be used.
Power20	1. ‘Rule of the thumb’	Narrative review	1. Time needs to be halved in order to achieve an image of equivalent density when the kVp is increased by 10 kVp.	1. Only suitable for a kVp between 60 and 80 kVp. If the kVp is outside this range there is an error of 3–5 kVp.
		2. Siemen's point system	2. Each region of anatomy is assigned points. The exposure parameters are also assigned points. If the sum of the points of the selected parameters matched the points of the anatomy being image then the exposure should be correct.	2. It fails at the extreme ends of the kVp range (40 and 117 kVp).
		3. Unit step radiography	3. Exposure parameters and patient thicknesses were assigned ‘units’ and an increase in one ‘unit’ equals a doubling of exposure.	3. It fails at the extreme ends of the kVp range (40 and 117 kVp).
		4. Variable kVp technique	4. The mAs is kept constant and the kVp is adjusted. An increase of 2 kVp is required for each centimetre increase in patient thickness.	4. This technique causes a variation in contrast between different patient thicknesses
		5. Optimum kVp technique	5. The kVp is ‘fixed at an optimum level of contrast’. (p. 11) The mAs value varies and is selected based on patient thickness.	5. None stated in article.
		6. 25% rule		6. Every cm increase of patient thickness requires a 25% increase in mAs.	6. None stated in article.
Eastman21	Body habitus factor	Description of the system(s)	The body habitus factor is found by dividing the patient's weight by their height. This value is then located on the chart provided in the article to find the appropriate exposure parameters.	None stated in article.
Eastman22	Bit system of technic conversion	Description of the system(s)	‘“Bits” are assigned to the factors controlling exposure such as kilovoltage and millampere-seconds’. (p. 75) ‘As long as the Bit totals remain constant, film density remains approximately constant’. (p. 76)	None stated in article.
Kratzer23	Supertech	Description of the system(s)	A system comprised of 3 charts. Chart A has a list of projections and a slider behind it. The slider is moved in order to display the measured thickness in the box next to the projection. Chart B provides correction factors for a change in FFD, grid, screen, aluminium filter, density and other minor factors. Chart C provides ‘200 combinations of kilovoltage, milliamperage, and time’. (p. 146)	The paper is not clear on how these three charts work to provide an adjusted exposure factor.
Atkins24	1. Bit system of technic conversion	Narrative review	1. ‘Increasing one whole number in the Bit System, doubles the exposure, with a corresponding increase in density’. (p. 389)	1. None stated in article.
	2. The thumb rule		2. ‘As you double milliampere seconds, you reduce kilovoltage by 10 kilovolts’. (p. 389)	2. This only applies when the kVp is decreased from 80 kVp to 70 kVp
	3. Variable kilovoltage technique		3. ‘Milliampere seconds … are kept constant and kilovoltage is varied by 2 kvp. per centimeter of thickness’. (p. 389)	3. A change in kVp also leads to a change in contrast.
	4. Optimum kilovoltage technique		4. ‘When milliampere seconds and adequate kilovoltage values are established for the average patient, one half the milliampere-seconds value is then used for the small patient, and twice the milliampere-seconds value is used for the large patient’. (p. 389–390)	4. None stated in article.
	5. Automatic exposure control (AEC)		5. This technique involves employing a ‘fixed voltage and fixed milliamperage, with the time of exposure determined by the sensing device’. (p. 390)	5. Incorrect centring leads to an incorrect exposure.
Stopford25	Log10 technique chart	Description of the system(s)	Log10 factor is the value needed to increase the parameter per cm. Log10factor = [log10(of mAs for large) – log10(of mAs for small)]/(cm difference) Allows you to develop charts with mAs provided for each cm. The same can be done for kVp.	None stated in article.
Markivee et al.26	1. AEC	Description of the system(s)	1. ‘Terminates the X-ray beam when a preset level has been accumulated’. (p. 113)	1. Errors in exposure occur when ‘the detector is not correctly positioned over the “critical” part of the body’ (p. 113) ‘it is correctly positioned but the critical part is unusually radiolucent or radiodense’ (p. 113) ‘it is correctly positioned but the remainder of the anatomy to be X-rayed is unusually radiolucent or radiodense’ (p. 113) A film/screen combination is different to the combination the AEC is calibrated to.
	2. Unit step radiography		2. An exposure value scale (XVS) number is assigned to the centimetre thicknesses of body part and can be alter to suit the tissue composition. XVS numbers are also assigned to the values of the exposure parameters; kilovoltage, milliamperage and time. An accurate exposure comes from the selection of parameters whose XVS total matches the XVS of the anatomy to be imaged. Exposure parameters can also compensate for changes in ‘film speed, screen speed, target-to-film distance …, single phase or three phase power supplies, half wave or full wave rectification and the numerous patient variables’. (p. 114)	None stated in article.
	3. Computer program		3. Based on a modified version of unit step radiography to match the modern day techniques. It requires the input of ‘patient, equipment and other physical factors’ (p. 114) which leads to a total XVS number which in turn leads to a set of exposure parameters being displayed. Three sets are displayed which vary in kVp by 1 XVS number but all will produce the same density image. It is possible to adjust technique to different electrical powers and different amounts of filtration.	3. Errors occur when the patient isn't properly measured. Using the system increases the time required per examination. Wide coverage of factors that influence exposure increase amount of input data required and thus increases length of each examination.
Horsington27	Computer program	Description of the system(s)	It requires the input of a variety of factors to allow the calculation of a new exposure, which are tissue thickness, bucky or non-bucky, grid, SID, whether the lungs are in the region of interest and whether an intensifying screen is being used. Once all information has been collected, kVp and mAs will be displayed. The operator has the option of changing one of these values to get a different set of parameters.	None stated in article.
Enright28	Linear logarithmic relationship between mAs and patient thickness	Phantom Study Measure mAs need for varying patient thickness at each constant kVp. 60–120 kVp was tested at 5 kVp increments. Grid ratio used was not indicated. SID set at 100 cm	Using phantoms that represent the maximum and minimum thicknesses of the region and finding the optimal mAs and graphing a line between those two points to find appropriate mAs for thicknesses between the two thicknesses used.	This technique doesn't account for tissue composition.
Lewis29	Computer program	Description of the system(s)	It requires the input of a variety of factors to allow the calculation of an appropriate set of exposure parameters that is displayed. The factors requested are body part, projection, intensifying screen, initial exposure factors and the exposure factor to be adjusted.	None stated in article.
Kelly30	1. Half value layer (HVL)	Description of the system(s)	1. ‘An increase in tissue thickness of 3 cm would require that the “Base” exposure be doubled to maintain the required film density’. (p. 19)	1. None stated in article.
	2. 25% rule		2. Every cm increase of patient thickness requires a 25% increase in mAs.	2. Exceptions to the rule exist. i.e., for chest X-ray and thickness >25 cm a 25% increase in mAs per 1.5–2 cm increase in thickness.
	3. 15% rule		3. A 15% increase in kVp requires a 50% decrease in mAs in order to achieve the same exposure.	3. None stated in article.
Sterling31	AEC	Description of the system(s)	The AEC ‘terminates the exposure when the proper level of radiation has been reached’. (p. 422) This allows the X-ray system to provide ‘consistent radiographic densities’. (p. 426)	Incorrect positioning and/or chamber selection and/or bucky selection will lead to incorrect exposure. The desired exposure time needs to be greater than the minimum response time. The backup timer needs to be the maximum exposure required in case of malfunction The ‘AECs must be calibrated for the film screen combination in use’ (p. 425) and ‘to provide the required image density with the film screen combination in use’. (p. 426)
Artz3	AEC	Description of the system(s)	A radiation detection device is place in front of or behind the image receptor and measures the residual X-ray beam. When sufficient X-rays have reached the detector the beam is stopped.	None stated in article.
Al-Balool and Newman32	1. 25% rule	Water bath used to simulate a patient. 50–150 kVp at 10 kVp increments was tested. Grid and non grid was tested for the whole kVp range. SID = 100 cm	1. Every cm increase of patient thickness requires a 25% increase in mAs.	1. The 25% rule only works well for most radiographic situations (low kVp with no grid and high kVp with a grid).
	2. 15% rule		2. A 15% increase in kVp requires a 50% decrease in mAs in order to achieve the same exposure.	2. The 15% rule is less reliable as the factors that affect the required mAs adjustment are patient thickness and the amount of mAs change required per kVp.
Carroll33	1. 15% rule	Description of the system(s)	1. A 15% increase in kVp requires a 50% decrease in mAs in order to achieve the same exposure.	1. None stated in article.
	2. Half value layer		2. ‘Every four centimetres of thickness requires a change in mAs by a factor of two’ (p. 154).	2. None stated in article.
	3. Optimum (fixed) kilovoltage technique		3. A kVp is found for each part of anatomy that provides the best contrast and then is keep constant. The mAs is set as the maximum the desired focal spot size can accommodate. The optimal time is selected for an average patient. The time is double when a thicker an average patient is examined and halved for a smaller than average patient.	3. None stated in article.
	4. Variable kilovoltage technique		4. The optimal mAs needs to be found for each region and is then kept constant. The kVp is selected by multiplying the thickness of the anatomy of interest by 2 and adding 40.	4. Altering kVp results in differences in contrast of images of the same region for different patient thicknesses or a change in contrast of images of the same region but differing projections.
	5. AEC		5. A detector, either an ion chamber or photomultiplier tube, is the used to measure the exit beam that reaches the film/image plate. When a preset amount of radiation has reached the detector the exposure is stopped.	5. It is not effective when imaging anatomy smaller than the detector, when the detector is not completely covered by anatomy, when positioning and/or centring are incorrect, when collimators are too wide increasing scatter radiation and when implants are covering the detector.
Schueler34	1. 10 kVp rule	Description of the system(s)	‘An increase of 10kVp is equivalent to doubling the milliampere-seconds’. (p. 732)	It only works for a small range 60–100 kVp
McLean and Targett35	25%/cm rule	Water bath used to simulate a patient. The mAs needed for 1 cm increase in water depth was measured. No grid was used for 50–70 kVp and a grid used for 70–117 kVp SID = 100 cm.	Every cm increase of patient thickness requires a 25% increase in mAs.	It works for most radiographic situations. Exact adjustment varies a few percent, which has a negligible effect on image quality
Fauber36	1. 15% rule	Description of the system(s)	1. A 15% increase in kVp requires a 50% decrease in mAs in order to achieve the same exposure.	1. None stated in article.
	2. AEC		2. A radiation detection device is place in front of or behind the image receptor and measures the residual X-ray beam. When sufficient X-rays have reached the detector the beam is stopped. The AEC only controls the time factor so kVp and mA still need to be set.	The AEC requires correct centring and detector selection, as incorrect centring and/or detector selection will result in an over- or under- exposed image. The AEC cannot distinguish between scatter and primary beam so wide collimation will lead to premature automatic cut-off.
Bontrager37	1. 15% Rule	Description of the System(s)	1. A 15% increase in kVp requires a 50% decrease in mAs in order to achieve the same exposure.	1. None stated in article.
	2. AEC		2. ‘These systems provide automatic termination of exposure time when sufficient radiation (exposure) is received by the selected ionisation chamber’. (p. 36)	2. None stated in article.
Eastman38	1. AEC	Summary	1. The AEC uses ‘either a photocell or ionisation chamber … to terminate exposure when sufficient remnant radiation has reached the receptor’ (p. 202).	1. None stated in article.
	2. Body habitus technique		2. There is a chart for each body type (hypersthenic, sthenic, hypostenic, or asthenic) and the patient is categorised as one of these types and the corresponding chart is consulted. ‘Both kVp and mAs vary’ (p. 202).	2. None stated in article.
	3. Variable kilovoltage technique		3. The ‘mAs remains constant and the kVp changes according to the size of the anatomical part’. (p. 202) Increase the kVp by 2 for every centimetre increase in thickness.	3. None stated in article.
	4. Fixed kilovoltage technique		4. The ‘kVp remains constant and mAs is used to compensate for patient size’. (p. 202) The patient is classified as small, medium or large and the exposure is adjusted accordingly.	4. None stated in article.
	5. High kilovoltage technique		5. This is where the ‘fixed kVp technique … [is used] in the higher kilovolt peak range (100–150 kVp)’. (p. 203)	5. None stated in article.
DuPont™39	DuPont™ bit system	Exposure adaptation system chart	A ‘bit’ value is assigned to the values of each factor. The radiographer calculates the ‘total bit value’ for a ‘standard’ set of parameters. Whenever a factor changes from the ‘standard’ parameters, the radiographer needs to work out the new ‘total bit value’ and adjust the parameters in order to return to the value of the ‘standard’. A change of 1 ‘bit’ equals a doubling, or halving, of exposure.	None stated on system.