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Table 1 Parameters relevant in characterizing historical radiographs

From: The skin dose of pelvic radiographs since 1896

Modern parameter Old information (pre-1927)
Peak high-voltage (kVp) Equivalent spark gap on functioning tube
Hardness X-rays according to penetrometer or half value layer in water
Electrical information on primary and secondary circuit
Tube current (mA)a Average current, after 1904 often specified
Electrical information on primary and secondary circuit
Exposure time (min, s)a Explicitly specified duration of exposure
Target (anode) material Explicit or implicit: before 1912 platinum (Pt), then replacement by tungsten (W)
Filtration Implicit: no filter added, i.e. tube envelope only. Later sometimes specified filter
Exposure geometry Focus-plate or focus-patient distance, field size, type of study
Backscatter factor kVp-info, filtration, object thickness, expo-geometry. Explicit BSF seldom & later
  1. aOften only product of tube current and exposure time was reported (unit: mA.min or mAs)