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Transferring Images and Basic Teleradiology

Once the images are stored on a PC, it is relatively easy to transfer these images to distant locations for reporting or second opinions. The transfer of images to distant locations can be simplistically defined as teleradiology.

DICOM-Based

Teleradiology requires the following components

1. Sending station

2. A method to carry the images

3. Remote viewing station

2. Methods of Carrying Images

We start with this first, as it impacts what we need at the sending and viewing station ends.

The following methods are available

a. Direct dial-up

b. Direct cable or wireless connection

c. Internet

a. Direct dial-up.

In this, the sending station and the remote viewing station are directly connected through standard telephone lines using 56.6kbps modems at both ends or with ISDN lines. ISDN is a dying technology and does not work very well in India and so I will not talk about it further.

Obviously direct dial-up works best when the dial-up is at local call charges, for e.g. from the centre/hospital to one's house or to another centre in the same city or neighboring city under the same local call coverage. The disadvantage however is that the maximum speed is limited to 56.6kbps and in reality is usually less.

b. Direct cable connection

In a city like Mumbai, where the entire city is wired overhead with cables, it is theoretically possible to lay a direct cable between two centres, provided the same cable company services those areas. Using routers at defined intervals (needed to boost the Ethernet signal), the sending and remote viewing stations can thus be connected as if on an Ethernet and images can be transferred. The disadvantages are the initial high cost of laying the cable and the need for constant maintenance of the routers. This is not a very viable alternative especially with the advent of faster Internet connections.

c. Internet

Images can be transferred over the Internet either by attaching them to email or by directly transferring them to a central web server from where they can be downloaded.

The way in which this can be done is totally dependent on the bandwidth available. If only dial-up Internet accounts are available, then the maximum speed available will be 56.6kbps, which is pretty slow. If cable or DSL are available, then must faster speeds are possible (upto 384Kbps), depending on the ISP (Internet service provider).

Email attachments of images allows uploading to specific recipients, but is slow and there are limitations to the amount of disk space that emails can consume on most email accounts. Transfer to a web-server allows upload and download using ftp protocols and is a better way of working, but would require someone to maintain a web-site and server with reasonable hard-disk space.

1. Sending Station

The sending station would be our simple viewing and archival workstation that has been described in the preceding chapters.

Depending on the mode of transfer, the .dcm images can be transferred either directly or after they have been compressed. With higher bandwidths, the .dcm images can be transferred directly (a typical CT image is 512K, i.e. half MB, whereas MR images can range from 133 to 512K depending on the acquisition matrix).

With lower bandwidths, compression is a must. Using IrfanView or ImageJ, it is possible to batch-convert (i.e. convert multiple images at one go) .dcm images to .jpg images, which typically are between 5-25K in size. Upto 30% loss of detail is to be expected with the loss of the ability to change window width and level. However a typical CT brain study consisting of 40 images or so, after compression, would be of a total size of approximately 800K and would take about 3-5 minutes or so to transfer and upload or download.

3. Remote Viewing Station

The remote viewing station should be a standard PC with at least 128MB of RAM and a 17" or 19" high-end monitor.

If the images transferred are compressed .jpg images, any shareware viewer such as IrfanView can be used for viewing these images. If the images transferred are the actual .dcm images, any of the viewers such as Osiris or AccuImage Lite can be used.

Another way or viewing images is by using remote access software such as PCAnywhere or CarbonCopy or GoToMyPC.com, These can be accessed either through direct dial-up or through the Internet. These softwares work by allowing the remote viewing station to gain access to the sending station and to control it. The desktop of the sending station becomes the desktop of the viewing station and by just transmitting mouse or keyboard clicks, the sending station can be controlled.

For example, after the remote viewing computer logs into the sending station, the desktop screen of the sending station becomes the desktop screen of the viewing station. If we click on the AccuImage Lite icon and open the software, it is the software on the sending station that will open. It may take between 10-30 seconds for the desktop screen on the remote viewing station to refresh depending on the speed. Then the images on the sending station can be viewed, one after another, without actually transferring the images across.

Non-DICOM Image Transfers

For teleradiology, if the modality is non-DICOM or not on a DICOM-network, it becomes necessary to digitize the images so that they can be made available to the sending station. This can be done using

a. scanners

b. digital cameras or

c. video capture cards

Digital cameras with a 3 megapixel or higher resolution can serve basic needs and can replace the need to use scanners, which take more space and are less versatile. Video-capture cards work best for ultrasound machines, the majority of which are non-DICOM. Once the images are digitized, they will be available either in .tif or .jpg formats and they can then be transferred using the various methods described in the "DICOM-based" section.

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