Correspondence by hilen


									1996, The British Journal of Radiology, 69, 283-284

(The Editors do not hold themselves responsible for opinions expressed by correspondents)

Transmission titles for X-ray mattresses                                 transmission characteristics. This situation will only change when
                                                                         the users demand that they do so.
                                                                                                                        Yours etc.,
                                                                                                                                  J MAUGHAN
The Editor—Sir,
                                                                                                                                M BURNISTON
Considerable attention has been given to the introduction of carbon
                                                                                                                                M ROBERTSON
fibre components such as table tops in the implementation of a
                                                                         Departments of Medical Physics and Radiology
patient dose reduction programme. There appears to have been
                                                                         St James's University Hospital
much less interest in the attenuating properties of the mattresses
                                                                         Beckett Street
     With the assistance of Medical Technical Officers we have
                                                                         LS9 7TF
surveyed a range of tables and mattresses used in our hospital. The
                                                                         {Received 8 September 1995 and in revised form 9 October 1995,
results were disturbing. Figure 1 shows the distribution of table and
                                                                         accepted 23 October 1995)
mattress transmission values. Mean value for the tables was 82%
with a range 74-89% and the mean value for the mattresses was 91 %
with a range 81-98%. Only one of the table tops was made from
carbon fibre and this had a transmission value of 89%.
     Measurements were made at 80 kVp, 20 mAs or the nearest             Femoral angiography using the reverse
available setting with a focus to chamber distance of approximately      shuffle technique
1 m. At least three radiation output measurements in air were made,
followed by three measurements with the table top between the
focus and chamber and three further measurements with the mattress
                                                                         The Editor—Sir,
in place. The measurement in air was then repeated. In one case
                                                                         Oxtoby et al [1] compare the bolus chasing method of peripheral
several mattresses were available for the same table. Transmission
                                                                         angiography unfavourably with their own ingenious reverse shuffle
measurements were also made on matttress samples sent to us for
                                                                         technique, in which a remarkable 98% success was achieved in
                                                                         terms of timing on the first run. The quoted paper on bolus chasing
     Patient comfort is obviously an important consideration in the
                                                                         by Jurriaans and Wells [2] does in fact refer to repeat runs for
choice of mattress. However, the mattress results did demonstrate
                                                                         subtraction purposes and for obtaining oblique views, rather than
that the cover material plays a large role in the attenuation of the
                                                                         because of timing errors.
beam and that a thinner mattress does not necessarily give rise to a
                                                                              We have used a bolus pacing method of peripheral angiography
substantially higher transmission value.
                                                                         in Harrogate for 4 years. As in Plymouth we have found that
     These results highlight that large investments in the purchase of
                                                                         acquisition of images in real time necessitates repeats only to
carbon fibre table tops may not result in the desired patient dose
                                                                         enhance the original information rather than to correct timing errors.
reduction if attention is not also given to the choice of mattress.
                                                                         Our method of driving the table differs from the manually driven
Mattresses are currently specified only in terms of cover, material
                                                                         Plymouth technique in that it steps automatically with one or two
and thickness and manufacturers seem uninterested in specifying
                                                                         digital spot images acquired at each stage. However, as these images
                                                                         are seen in real time the table can be stopped at any step if its
                                                                         movement is outpacing that of the bolus. Timing accuracy is
      Number of tables/mattresses                                        therefore no longer an issue.
                                                                                                                             Yours etc.,
 12 -                                                                                                                                J F ROSE
                                                                         Department of Radiology
                                                                         Harrogate District Hospital
                                                                         Lancaster Park Road

                                                                         HG2 7SX
                                                                         {Received 2 October 1995 and accepted 1 November 1995)

        70-75      76-80      81-85      86-90        91-95   96-100
                                                                         1.OXTOBY, J W, YEONG, C C, SINGANAYAGAM, J ET AL,
                             % Transmission                                 Technical note: Femoral angiography using the reverse shuffle
                        • i Table     H i Matttress                         technique, Br. J. Radiol, 68, 1014-1016 (1995).
                                                                         2. JURRIAANS, E and WELLS, IP, Bolus chasing: i new technique
Figure 1. % Transmission through tables and mattresses.                     in peripheral angiography, Clin. Radiol, 48, 182-185 (1993).

Vol. 69, No. 819                                                                                                                          283

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