|A COMPARISON OF THE RELATIVE VALUE OF SINGLE AND
DOUBLE PICTURE TECHNIQUES IN TB PREVALANCE SURVEYS
|Raj Narain, SS Nair & P Chandrasekhar: Indian
J TB 1964, 11, 145-53.
Limitations of a single X-ray picture for locating
and interpreting shadows in the chest had been studied earlier.
In order to reduce these limitations, it was suggested that two
pictures of each person be taken where the second picture was to
be taken after a vertical displacement of X-ray tube, up or down
by about 4 to 5cms. The advantages of taking two pictures simultaneously
as compared to a single picture have not been studied so far. Two
mobile X-ray units each with an odelca camera were alternated for
the single and double picture examinations. A total of about 2,000
persons were X-rayed and were read independently by 3 readers. A
spot sample of sputum was collected 3-4 days later from persons
with abnormal X-ray shadows and was examined by direct smear microscopy.
Comparison of the readings of the two sets of pictures
did not show a better agreement between different (inter-
individual) readers or between two different readings of the same
reader (intra-individual) when the two picture technique was used.
The X-ray cases detected by double picture only by any one reader
were not confirmed, more often than those detected by single picture
only. The X-ray pictures of the bacillary cases were also not interpreted
more often as active tuberculosis by the two picture technique.
It was concluded that the double picture technique does not offer
any advantage over the single picture technique.
|KEY WORDS: SURVEY, PREVALENCE, X-RAY READING, X-RAY
FILM, SINGLE PICTURE, DOUBLE PICTURE.