Image storage

Published on 12/06/2015 by admin

Last modified 22/04/2025

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8 Image storage

The ability to store patient information in a format that means that it is secure, can be readily accessed by authorised users only and the information does not degrade over time

Storage criteria

Security	Unauthorised viewing of data should not be possible and therefore: Passwords • Need to be changed on a regular basis • Linked to each individual user • Use of automated password generators (APG) Hand held device (unique to each person authorised to use the system) Person requests a password APG server sends a password User inputs the password The password is changed every time the user goes onto the system Firewalls • Automatically identify information coming from external sources Either allow information in, e.g., from a GP surgery Or exclude information, e.g. from external viruses • Part of the internal network • Should be updated at regular intervals Antivirus software • Software packages to protect against Viruses Worms Cookies • Viruses, etc. gain access via internet connections including e-mail • Software should be updated at regular intervals • Regular checks should be run on stand-alone computers with internet access Individual monitor security • Antivirus software should be run at regular intervals • Internal security settings should be set at high: Firewall – on Block cookies Block pop-ups Allow automatic updates for firewalls and antivirus software • Cookies should be deleted at regular intervals Removal of external disk drives • Consider blocking or removing external disk drives • Prevents the introduction of viruses from external computers via CDs and DVDs
Access	Limited to the requirements of each user, e.g. • Managers limited to management information • Clinicians limited to patient details; all information contained in patient records • Receptionists limited to patient’s contact details, clinic lists • Individual passwords used and changed at regular intervals • Automatic record of: Who accessed a file The date and time is was accessed Who added to the file Who deleted part of a file.
	Note If part of the file is deleted it should remain on the record but show it has been deleted, e.g. with a line through the record
	• It is important that staff: Log off as well as log on to the computer Do not give anyone their password Do not write down their password
Speed of Access	• It is important that patient information can be found quickly and easily • Optical disks allow quick and easy access • But have problems due to the size of radiographic images • Images will be stored on the World Wide Web • On a dedicated site • With a dedicated search engine to recall the information
Stability	• Stored images should not degrade over time • Storage media needs to have a long life and equipment needs to be available to read the image at a later date
Stability	Note New computers cannot read floppy disks, so any information stored on these is no longer accessible • Storing images on the World Wide Web may solve these problems
Backup	• Backup is important in case of breakdown or virus attack • Information should be backed up automatically • A separate copy of all data should ideally be stored away from the main site. If this is not possible, a dedicated room should be used • It should not be stored on the same intranet system
Storage Capacity	• A capacity of 0.6 Gbytes, would be capable of storing all details, reports, film locations, appointments, X-ray room details, registrations, etc. for about 1 million patients • That represents the storage of all patient data (in an average hospital) for about 10 years
Storage Capacity	But • 2.5 Gbytes is only capable of storing about 170, 35 × 43 cm chest films • Data compression may be able to reduce storage requirements by as much as 50% • Again storage on the World Wide Web will solve these problems

Storage formats

Magnetic Tape Digital Audio Tape (DAT) Digital Linear Tape (DLT)	Construction • Plastic tape • Coated with iron oxide • The surface can be magnetised • The tape can be purchased in a variety of widths • An 8-bit tape will have 9 tracks 8 tracks to store data plus 1 track for the computer to check the data Storage of data • Utilises the principle that electricity can be on or off • The information from the computer is in binary (hexadecimal) format • The signal is made up of a pattern of ‘on’ and ‘off’ • If ‘on’ hits the tape it becomes magnetised forming a ‘spot’ • If ‘off’ hits the tape it is not magnetised • The information is therefore built up across the tape • A frame is a complete data set • An inter-record gap (IRG) separates each frame Reading • Tapehead scans the tape • Detects the magnetised areas on the tape • Translates them into a signal to send to the computer Advantages • Used for backing up data • Inexpensive • Large memory, e.g. 5 Gbytes Disadvantages • Time taken to access data as patient information may be in different areas on the tape • Tapes have to be periodically rewound to prevent degrading of the magnetic information
Memory Sticks	Type • A solid state storage device Construction • A chip with a grid of columns and rows • Two transistors at each cell (where each area of the grid intersects) Floating gate transistor Control gate transistor Separated by thin layer of oxide Storage of data • Utilises the principle that electricity can be on or off • The information from the computer is in binary (hexadecimal) format • The signal is made up of a pattern of ‘on’ and ‘off’ • Initially all cells have a value of 1 • If an electrical charge is put on the floating gate: The float gate transistor acts as an electron gun The electrons from the transistor pass through the oxide layer giving it a negative charge A cell sensor monitors the charge on the oxide layer If the charge drops below 50% the cell value changes to 0 The information is therefore built up across the cells Reading • The card is electronically scanned to reconstruct the data Advantages • Small in size • Allows fast access to data • Easily transportable • Plugs into any USB port Disadvantages • Expensive • If used on infected machines can introduce viruses, etc. into the hospital system
Optical Disks
Compact Disk (CD)	Types • CD-R Compact disk recordable • CD-RW Compact disk re-writeable Construction CD-R • Outer protective coating Lacquer • Reflective layer – thin metal Gold, silver alloy, or silver • Recording layer – organic dye Phthalocyanine or azo • Plastic substrate – contains a spiral groove extending from the centre of the disk to the outside edge Polycarbonate Fig. 8.1 CD construction.
	Construction CD-RW • Outer protective coating Lacquer • Reflective layer – thin metal Aluminium • Dielectric layer Zinc sulphide, silicon dioxide • Recording layer – phase change alloy Indium, silver, tellurium and antimony • Dielectric layer Zinc sulphide, silicon dioxide • Plastic substrate – contains a 0.5 μm (micron) spiral groove extending from the centre of the disk to the outside edge Polycarbonate Storage of data • Information written on the disk by 405 nm (nanometre) laser • The signal is made up of a pattern of ‘on’ and ‘off’ • If ‘on’ hits the disk the dye layer is heated and darkens • If ‘off’ hits the disk the dye remains unchanged • The information is therefore built up across the disk Reading • A 405 nm laser scans the disk from the inside outwards • Detects the blackened areas on the disk • Translates them into a signal to send to the computer Note A variable motor is used as: • The diameter of the grove is smaller in the centre than the outer edge • It ensures that the information is read at a constant rate across the disk • Speed of reading/writing is dependent on the drive speed of the computer drive Advantages • The laser is focused below the disk surface therefore scratches and blemishes are not read • Any image can be found in about a quarter of a second • Inexpensive Disadvantages • Have a storage capacity of only 650–800 Mbytes • Are being replaced by DVDs
Digital Versatile Disk (DVD)	Types • DVD−R • DVD+R • DVD−RW • DVD+RW • Either single (a recording side and a dummy side) • Or double-sided (two recording sides) Construction (single-sided) DVD–R • Outer protective coating Lacquer • Reflective layer – thin metal Silver, silver alloy, gold • Recording layer – organic dye, e.g. Azo, cyanide, dipyrromethene • Plastic substrate – contains a 0.5 μm, spiral groove extending from the centre of the disk to the outside edge Polycarbonate Number of indentations (pits and lands) between the grooves • Adhesive bond • Dummy layer Polycarbonate plastic Construction (double sided) DVD+R • Outer protective coating lacquer • Reflective layer – thin metal Silver, silver alloy, gold • Recording layer – organic dye, e.g. Azo, cyanide, dipyrromethene • Plastic substrate – contains a 0.5 μm, spiral groove extending from the centre of the disk to the outside edge Polycarbonate • Adhesive bond • Plastic substrate – contains a 0.5 μm, spiral groove extending from the centre of the disk to the outside edge Polycarbonate • Recording layer – organic dye, e.g. Azo, cyanide, dipyrromethene • Reflective layer – thin metal Silver, silver alloy, gold • Outer protective coating Lacquer Construction of a (single-sided) DVD–RW • Outer protective coating Lacquer • Reflective layer – thin metal Silver, silver alloy, aluminium • Dielectric layer Zinc sulphide and silicon dioxide • Recording layer – phase changed alloy, e.g. Indium, silver, tellurium and antimony or germanium • Dielectric layer Zinc sulphide and silicon dioxide • Plastic substrate – contains a 0.5 μm, spiral groove extending from the centre of the disk to the outside edge Polycarbonate Number of indentations (pits and lands) between the grooves • Adhesive bond • Dummy layer Polycarbonate plastic Fig. 8.2 DVD−RW construction.
	Storage of data • Information written on the disk by 405 nm (nanometre) laser • The signal is made up of a pattern of ‘on’ and ‘off’ • If ‘on’ hits the disk the dye layer is heated and darkens • If ‘off’ hits the disk the dye remains unchanged • The information is therefore built up across the disk Reading • A 405 nm laser scans the disk from the inside outwards • Detects the blackened areas on the disk • Translates them into a signal to send to the computer Advantages • The laser is focused below the disk surface therefore scratches and blemishes are not read • Have a storage capacity of up to 60 Gbytes and up to 240 Gbytes is predicted • Any image can be found in about a quarter of a second Disadvantages • DVD+ disks will only work on DVD+ equipment • DVD− disks will only work on DVD− equipment
Magneto-optical Disks	Construction • A ferromagnetic material with a plastic coating • With an electromagnet positioned behind the disk Storage of data • The disk is scanned twice by a pulsed laser The first scan erases the disk – The light varies in intensity and heats up the surface to the Curie temperature – Curie temperature is the temperature at which the surface loses its magnetism The second scan enables the electromagnet to ‘write’ on the disk • The heating allows the electromagnet to change the polarisation of the disk material Reading • A 405 nm laser scans the disk from the inside outwards • Detects the magnetised areas on the disk • The reflected light therefore varies in intensity forming the image Advantages • 2.8 Mbytes of data can be stored • Very reliable, as data is automatically checked at the end of writing Disadvantages • Writing the data is slow due to the double laser scan
Juke Boxes	Construction • An electromechanical device Storage of data • Contains a number of optical computer disks Reading • Enables automatic retrieval of archived material Advantages • Allows access to a number of optical disks • Additional juke boxes can be added to the system • Cost-effective Disadvantages • Long retrieval time
World Wide Web	Construction • Potential for a global area network for NHS Data Storage of data • On the network therefore with unlimited capacity Reading • Using a search engine (similar to Google) • Search for: Hospital Patient Conditions, etc. Advantages • All patient data available worldwide • Images taken in one country would be available in another • Unlimited storage • Fast access to information • Enable researchers to have access to anonymised information Disadvantages • Potential harm from computer virus attack • Potential confidentiality problems with computer hackers

Digital and Radiographic Imaging A Practical Approach

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