Re: Warning of major NHS IT overspend

[Brian Beesley <[EMAIL PROTECTED]>]

On Tuesday 02 November 2004 02:16, Adrian Midgley wrote:
> On Monday 01 November 2004 09:36, Brian Beesley wrote:
> > > and that locally relevant documents that require a lot
> > > of storage (such as a decently readable scan of an x-ray) will be
> > > retained in analogue film form at the point of generation, and only a
> > > reference made in the database as to their existance.
>
> Remember that analogue films are on the way out.

Fashion!

> It is unlikely that a new X-ray department would be built in the UK that
> was not a direct digital one - Picture Archiving - PAC systems are popular
> for several reasons, but one that may not be entirely appreciated is that
> if you consider the bits around a film or several films, like somewhere to
> walk to get them and so on, the volume of storage required in the hospital
> for film may be both larger and more expensive than the volume required for
> digital images.

Probably you haven't factored in the space, installation and running costs of 
providing air conditioning to keep the storage system operating. They have a 
far higher power/volume requirement than film stores, which are essentially 
passive structures.
>
> The detectors also (I gather) are more sensitive than the emulsion, so the
> radiation dose to the population is lower.  THat is counfounded by various
> improvements, but seems likely in itself anyway.

If the detectors _are_ more sensitive than the emulsion, the resolution must 
be lower. X-ray film is as sensitive to X-ray radiation as is physically 
possible i.e. one photon affects _at least_ one silver halide crystal in such 
a way that it will darken during development. To get more sensitivity you 
have to make the area of the detectors bigger than the silver halide 
crystals. As X-rays are essentially unfocussable this implies directly that a 
more sensitive detector must have less resolution.

I simply don't know how many X-ray diagnoses depend on resolution of the 
order of 0.01mm, which can easily be achieved by silver halide emulsion. I 
would guess that 0.1mm (or more) is wholly adequate for some diagnoses but 
may be insufficient for others. 

As always, the benefits of digital imaging are elimination of the "messy" 
chemistry involved in developing and fixing the latent image and the 
associated time lag. 

There is a balance between quality, latency (time between exposure and 
display) and operating cost which may not always have the same solution.

Brian Beesley