Re: X-ray/digital/radiation dose

[osuleiman@comcast.net]

Et al-

I've followed the recent set of emails with interest. Let me share some of what is going on medically.

Digital medical imaging has been around a few decades, but only until recently have the economics become favorable due to the large consumer mass market. In the early 1980's PACS and digital were being advocated, only now is it truly arriving. Digital image quality continues to improve, but may never (although I never should say never), approach the detail, or spatial resoltion of film, which is on the order of 100 line pairs per mm. More on that later.

Film Companies and Digital Imaging

Don't worry about the film companies, e.g. Kodak and Fuji, they all have been and continue to be active in the digital medical imaging area, most are involved in computed radiography (CR) or other digital imaging. They are aware of what's been happening for many years.

Film may be used more today than in the past, not as a direct recording medium, but for hardcopy records. Do we use more paper or less today? Although we don't use paper in a typewriter anymore, we generate paper copies with our laser printers. CT, MRI, and ultrasound generate lots of hardcopy films, but none of these imaging technologies uses film for direct recording purposes.

Will film be eliminated, probably yes, but when? It is being eliminated as a (1) direct recording medium as I write this, although it probably is being used more for (2) hardcopy archival purposes; but eventually, as users and readers have easier access to electronic/digital files, AND the ability to retrieve and view them on MONITORS readily available for (3) viewing, commonly referred to as SOFTCOPY display, then we will see the final chapter in film as we know it today.

Image Quality (Film vs digital)

Now, back to image quality for film versus digital. The human eye eventually limits what we can see. A few years ago we did a NEXT study with dental film, and realized that although we were scoring a distribution of wire meshes which the dentist or tech could see (wire mesh embedded in a phantom was one of our image quality tests), I realized that theoretically we should have been observing even the smallest wire mesh. When we rescored the images using a magnifying glass, we saw everything on the film. The take away lesson here is that technical superiority may not translate into the clinical environment.  The inherent spatial superiority of film is rarely used, and current digital detector and display technology meets most, but not all, clinical needs.

Contrast- With film you can either use a low contrast (dental), medium contrast(chest), or high contrast film (mammography), but each requires one exposure, and may involve many images...digital has the ability to level (contrast) and window (brightness or optical density), creating many images from one exposure. Digital also has other benefits in terms of image manipulation, and all of the other advantages associated with electronic files. Once digitized, an image can be analyzed by computer, usually referred to as computer assisted diagnosis (CAD). FDA has approved such systems as second readers.

Clincial studies continue to demonstrate that depending upon the clinical task, broken bone, tooth decay, cancer, either film or digital may be better. The other factor is the "observor". The late radiologist and medical physicist Carl Vyborny used to refer to the radiologist as perhaps the weakest link in the imaging chain, because of the inherent variability among these readers.

Digital is clearly making inroads in terms of diagnostic accuracy and patient throughput, but film still has some advantages. I suspect that small facilities will continue to use film for some time. 

Legal archival records

Regarding legal archival issues- that threshold was crossed when we went from film badges to TLD's, not a permanent film record, but a legal paper record.

Dose

Digital dental radiation doses are lower than film, because dental film does not use an intensifying screen, although panoromic and cephalometric techniques use intensifying screens, the traditional intraoral film is screenless and inherently requires a higher dose, dental entrance air kerma values for intraoral film is on the order of 1-2 mGy.

Other digital imaging techniques have the potential of delivering both higher or lower patient does relative to film/screen. Some recent observaions suggest digital photospot doses are lower in fluoroscopy than traditional spot films, pediatric CT doses can be lower, but have been unacceptably higher than necessary, E-speed film can reduce dental doses by 50% and has been in use for over a decade, computed radiography doses appear to be a bit higher, while digital radiography appears to be slightly less than comparable film/screen techniques.

Beware- digital imaging is more user friendly, hence more exposures on more patients may happen. But beware of generalities, CT in emergency rooms is highly efficacious, one would not argue against such use, CR also has advantages for use away from the radiology department, and improved image quality when compared to the average portable x-ray. Improved healthcare, but maybe more radiation.

So, in closing, when will we become filmless?

I guess when we go paperless, although my personal bank sends my electronic copies images of my checks and statements, I still print out a paper copy. 

Orhan S.



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In a message dated 5/8/04 6:37:28 pm, Peter.Vernig@MED.VA.GOV writes:







Film is passé and will probably soon be all but obsolete in this country. Digital imaging is here now and we switched over a year ago in radiology.







I did have an interesting discussion with a Senior Medical Physicist recently. It would appear that our regional Health Authority (Health Board) is moving towards replacing traditional film with digital imaging, for all the reasons mentioned previously. However the concern of the medical physics department was to ensure that it is possible to obtain the same degree of clinical detail in the digital image as is currently achievable on film. To this end they had been working toward producing tests and test pieces that could be used routinely to demonstrate that the necessary level of detail is obtained during digital radiography. As someone else has already identified (John Jacobus a.k.a crispy_bird) digital imaging still has some way to go to match the image quality of film. 



I'm sure that medical physicist in my local health board aren't alone in trying to establish how small a fracture or defect can be seen on a digital image. Can any of our friends on the medical side shed more light on this issue?



Regards,

Julian