Assessing the radiological progression of simple pneumoconiosis.

Abstract

The Medical Service of the National Coal Board has recently issued the fourth in a series of medical research memoranda, in which the results of studies carried out on various aspects of the health of men working in this large industry are made generally available (Liddell and May, 1966). This memorandum is concerned with the technical aspects of what seems at first a simple matter? detecting and measuring increases in the amount of abnormality attributed to simple pneumoconiosis in the chest radiographs of coalminers. Simple pneumoconiosis is classified under the International Labour Organization (I.L.O.) system into four categories of increasing profusion of small opacities. The uncountable number of visible small opacities forms a continuum of abnorm ality, and the progression which is to be detected, whatever its significance, is an increase in this number. Sometimes progression produces a change of category, when the increased number of opacities takes the film across a category boundary; some times an equal increase of the number of opacities leaves the category unchanged, the progression being entirely within the boundaries of the original category. Thus the number of changes of category seen, when a group of men is x-rayed on two occasions some years apart, is not necessarily a sufficient index of the amount of progression. It may depend too much on how the men's radio graphs were distributed along the continuum of abnormality on the first occasion, in particular on the proportion of films showing virtually no small opacities at all. A major improvement in an index of this kind was effected by LiddelPs (1963) dis covery that readers of radiographs could easily indicate for each film read whether the I.L.O. category above or below the one finally chosen had been considered as a serious alternative. In this way the 4-point scale of the I.L.O. classification was effectively turned into a 12-point scale, on which the number of steps taken by each man could form an index which would respond more closely to increases in the number of opacities in the man's film.