2D Mark & Trace - Frequently Asked Questions

Frequently Asked Questions

Contents

Coding Symbology, Reading and Verification
2D/Data Matrix codes – what are they?
Readers – can I use the same bar code readers that I use for my sets of instruments?
GS1 – What’s that all about?
If I read a code on an instrument, what will I see?
Code size – how big or small?
Readers and Verifiers – what’s the difference?

General
Tracking companies – Do they need to mark my instruments?
Instrument Damage – can marking harm my instruments?
Passivation – what is it and is it necessary?
Contamination – Can marks on instruments be a source of contamination?
Are codes permanent?
Cost of instrument marking/using an instrument marking service?
Warranty - Do you provide a warranty on the marks that you make?

Marking Methods
Methods of instrument marking – what are they?
Laser versus Dot Peen?
Dot Peen – Can I hold the instruments to be marked manually?
Lasers – are they dangerous?
Lasers – do I need fume extraction?
Laser Bonding – Is it permanent and can the material come off in a patient or washing/sterilizing processes?
Laser Bonding – Is the bonding material dangerous to use by operators?
Laser Bonding – Does it take longer?

2D/Data Matrix codes – what are they?
Instead of using any form of bar code we could apply a unique number to every instrument using any of the
marking methods described elsewhere. However, for these numbers to be legible they would need to be a minimum size in order to be read. Tracking tasks would require these numbers to be read and the numbers entered into a computer or written down. This would be time consuming and require considerable concentration to avoid errors. A far better system would be to apply codes as symbols that can be automatically read by readers attached to computers. This is the purpose of the 2D code. The barcodes that we are all familiar with is technically described as a linear or one dimensional code.

Barcode

The linear code consists of a series of stripes of different thickness with different size gaps between them. The code is read by sending out a light source to the code and measuring the reflection that comes back to the reader. Where the light hits a dark mark no light will be reflected back and it will be reflected from the white space between the marks. Software then reads the code from the reflections or absence of them and decodes the result into numbers or characters. The entire dimension of the code does not have to be scanned to read the code a light simply has to pass from one end of the code to the other, at any height, to read the code.

Because of the common application of barcodes and the need for them to be universally readable, there are precise rules regarding their size etc. and this alone makes them too large to apply to instruments, though of course we can apply them to tags on instrument sets

2D code 2 dimensional code

The two dimensional code (2D) usually used for instrument marking is a square or rectangular symbol containing a number of square blocks (described as elements). These are either black marks or areas that are not marked that show the original instrument surface. Unlike the linear/one dimensional code that is read by analysing the reflected light, the reading technique is to take a photograph of the mark and then to analyse the light and dark elements to decode it. All of the symbol has to be photographed in order for it to be recognised and then subsequently read/decoded. This is why the code is described as two dimensional (2D).
The 2D code allows more data to be held in a much smaller space than the linear code and can be as small as you are able to make it, though this means it may not be universally readable.

The number of individual elements used determines the amount of data that can be held:

For square codes with a 10 x 10 (100 elements) structure can contain 3 numbers (0 – 9) or a single character (A – Z, plus punctuation marks).

10x10 code 10 x 10

A code with a 12 x 12 (144 elements) structure can contain 6 numbers (0 – 9) or 3 characters (A – Z, plus punctuation marks).

12x12 12 x 12

A code with a 14 x 14 (196 elements) structure can contain 10 numbers (0 – 9) or 6 characters (A – Z, plus punctuation marks).

14 x 14

A code with a 16 x 16 (256 elements) structure can contain 24 numbers (0 – 9) or 16 characters (A – Z, plus punctuation marks)

Some thoughts –

It will be seen that the 10 x 10 code is of no use only allowing numbers to be from 0 – 999. The 12 x 12 code will allow numbers from 0 – 999,999. This would seem to be more usable, but if you require a prefix to identify the hospital, 6 numbers would be insufficient.

The 16 x 16 code allows up to 24 numbers (0 – 999,999,999,999,999,999,999,999). This is a seriously large number and allows us to apply prefixes, company/hospital identifiers etc. and have plenty of digits left over to identify the instruments. If using the GS1 system, this structure is the smallest that can be used, as up to 13 digits may be needed to identify that the instrument is an asset of a specific hospital.

You can see from the pictures above that the more elements in a given space, the smaller they will be and therefore the harder to read. For a 4 mm square code, each element will be only ¼ mm square. For a 1 mm square code each element will be 1/16 mm square.

The marks can suffer up to 60% damage and still be read and require a relatively low contrast rate in order to be read.

Readers – can I use the same bar code readers that I use for my sets of instruments?

The 2D code can only be read using a camera-based reader that use a small video camera to capture an image of a bar code. The reader then uses sophisticated digital image processing techniques to decode the bar code.

The ordinary bar code reader is much simpler. It sends out a light signal, which scans the code and measures the amount of light that is reflected. This allows it to distinguish the black bars from the white background and the width of the bars. This is very much a mature technology with such readers being seen in everyday use.

Most readers that read 2D codes will also read standard bar codes, but not vice versa.

GS1 – What’s that all about?

GS1 is an international not for profit organisation that provides a registration service and guidance (rules) for the use of bar codes. Its presence is widespread involving almost all retail, commercial and industrial bar coding applications.

In relation to set/instrument marking they provide the following:

A unique identifier for each hospital/business.

The type of bar code we use – that is to say the symbol dimensions, number of elements, readability measures, error checking etc.

A uniform structure for the numbering system used to identify sets and instruments, expiry dating etc.

In brief, the benefit obtained of using the GS1 method is one of assured uniqueness and uniformity.

Every one in the healthcare sector will be able to read each others instruments and identify which facility they belong to. While the unique element may not be seen as critical by many because their instruments do not leave their facility, they may do in the future either because a contingency plan has been implemented for a short term problem or because of a long term change of strategy.

It clearly makes sense, particularly for an organisation as large as the NHS for the same symbol type to be used to mark its instruments and the same readers (types and not specific makes) and to use a common numbering system. The alternative of not using a uniform system could restrict hospitals choice to the companies carrying out the marking, the provision of special code readers etc. and prevent competitive tendering.

This has been recognised by PASA in their documents – Coding for Success and Surgical Tray Identification. The use of the GS1 system is already in use in set/instrument marking in addition to Pharmacy/Patient Identification etc.

Membership of GS1 is free to individual hospitals within the NHS because of a national agreement which pays fees centrally. Non NHS organisations need to pay a registration fee, based on the turnover of their business.

2D Mark & Trace Ltd are members of GS1 and will be pleased to answer any questions you may have regarding the use of the GS1 system, registration etc.

Other useful resources
PASA surgical tray identification

If I read a code on an instrument, what will I see?

Not much of interest? The usual matrix of 16 x 16 elements allows up to 24 digits of data to be stored (0 – 9) or 16 alpha characters (A – Z plus some punctuation marks). Therefore you will not see a description of the product, a department etc. but only a long number.

If the GS1 code structure is used, a prefix of 8004 is used to denote that the item is an asset and this is followed by the unique hospital/company number which is between 7 and 9 digits long. If using a numeric only system as required by GS1, this leaves between 11 and 13 digits to identify the item.

Therefore if you read a number it will look something like this:

800450601776511246789011

Where the red characters are the asset prefix, the blue is the unique company number and the green characters are the unique identifier for the instrument.

Your tracking system will therefore only recognise a code as a number, which needs to be associated (linked) within the tracking system as being either part of a set or a supplementary instrument. You therefore need to enter the instrument description into the tracking system and link it to a specific set if necessary.

Code size - how big or small?

Size does matter! The larger the code size the easier it is for your operators to see it in order to present it to the reader. Also, the reading of the code by your reader will be easier/quicker if the code is large rather than small.

A typical code size is 4 mm x 4 mm as the sample below* though they can be larger. Codes of around this size are usually recognized as being the minimum code size that can be easily read when using the GS1 coding structure with dot peen markers. If using a laser marker, the codes can be significantly smaller with code sizes of around 2 mm x 2 mm being capable of being read. It is possible to read codes as small as 1 mm x 1 mm, but these are difficult to see, particularly on polished surfaces.

	1mm
	2mm
	2.5mm
	3.2mm
	4.mm

*Code sizes may vary due to screen resolutions etc. These are intended to be representations only.

When applying codes it is necessary to have an empty space around the code at least the width of an individual element (called the “quiet zone”) to allow the reader to recognise the presence of a code. This means that codes cannot be on the edge of instruments or up against hinges etc.

When 2D Mark & Trace mark instruments and supply equipment, we have a “Productivity” option which allows code sizes to be varied at the turn of a switch which avoids the need to either alter software or open new programs which can result in new codes to be entered. This feature allows us to mark large or small codes without affecting the flow of work.

Readers and Verifiers - what's the difference?

A code reader simply decodes a mark and inputs the number into your computer to identify a particular instrument.

A verifier will carry out the same job as the reader, but additionally it will provide a quality assessment of the code. It does this by taking a picture of the code and then analysing it for a number of different parameters. It will assess the contrast between the light and dark parts of the code, the number of errors present, the uniformity (squareness) of the individual elements and so on. It can be set up to provide a pass/fail assessment of each mark that is made or be used on a batch basis. A report is usually prepared which can be either stored or printed out.

The parameters that should be assessed are specified by GS1 together with the wavelength of light used to carry out the analysis, The use of a specified light creates difficulties, particularly with codes on highly reflective instruments and it may be necessary to use alternative methods to establish “real world” readability.

An aspect of the 2D code is that it can be read, even with a significant amount of damage. However, it is useful to know if you are producing good quality codes and not ones that are on the verge of readability as even a small amount of wear or scratching could render them unreadable.

For this reason, when we mark instruments we aim to verify every mark that we make. This is not always possible with very small marks, due to the discrimination (sensitivity) of the verifier, which has to be far greater than that of a simple reader.

You can view a typical Quality report here.

Tracking companies – Do they need to mark my instruments?

If you use the GS1 method or any other universal symbology, any competent organisation can apply the marks to your instrument and these should be capable of being read by off the shelf code readers.

If you are advised that there is something special or different about the marking methods utilised or the readers used by the system, you should work with your IT Department to establish exactly what is being offered and why it is unique to the tracking company?

2D Mark & Trace Ltd is ISO 9001:2000 accredited specifically for the marking of surgical instruments.

Instrument Damage - can marking harm my instruments?

Different processes result in different levels of risk. Where instruments are damaged by the marking process it can result in localised corrosion (rust). This can be rectified either as and when necessary or as a precaution, it does however involve an additional process and it is clearly best to avoid the risk/need in the first place.

Passivation – what is it and is it necessary?

Stainless steel is stainless (corrosion/rust resistance) because of a thin layer on its surface which is inert. This layer builds up either over time or as the result of a passivation process. The passivation process uses acid to create a surface layer that will not rust.

Instruments will be subject to such a process as part of their production. In the event that the layer is damaged or breached the instruments may need to be subject to a repeat process in order to prevent rusting in the damaged area.

The chemicals that can be used to passivate stainless steel are typically 20 – 50% nitric acid (not nice) or citric acid which is organic and safe to use (the acid found in oranges).

Passivation requires instruments to be clean and free from any lubricants and requires exposure to the acid for fixed times at specified temperatures.

Passivation is an additional process that you should aim to avoid – we do!

Contamination – Can marks on instruments be a source of contamination?

There is no evidence that suggests that this is the case. Anecdotal evidence would indicate that the use of coloured tape can be a problem. One only has to remove the tape to be horrified at what is under it!

Are codes permanent?

The codes applied by dot peen, laser marking, laser etching, laser bonding are all permanent marking methods. However, all of these methods are susceptible to mark damage as the result of abrasion (scratching), erosion or corrosion. The marks are able to withstand considerable damage and still be read, though this does depend on the quality of the mark when first made. If a mark is made that it is only just capable of being read, a tiny amount of invisible damage, is sufficient to render the code unreadable. This is why we verify every code that we make and provide an individual quality report.

Cost of instrument marking/using an instrument marking service?

Very reasonable! A tough question because it is dependent on so many variables. A few of these are:

The type of process you wish us to use?
The approximate number of instruments you wish to mark?
The period over which you wish these instruments to be marked?
Your location as accommodation costs may be incurred?
Whether you need night or weekend working?

Starting an individual instrument marking project, does not have to be expensive and irritating.

We have developed knowledge and the associated skills to help organisations successfully implement these processes and and improve productivity.

Warranty - Do you provide a warranty on the marks that you make?

No – this is because the failure to read a code can be due to a variety of reasons. If an instrument is scratched or abraded for example, it can render it unreadable. Some instruments presented for marking may be incapable of being marked due to such damage.

We try and avoid such problems at the outset by ensuring our customers are well informed, understand the different marking techniques and have been correctly trained, where appropriate. When we mark, we prefer to use a marking method that offers the best technical solution, but we cannot insist that this used. Similarly, the size of marks utilised and the quality of the code readers used all have an impact. When we mark instruments we strive to ensure that the quality of the marks we make are known by the use of verifiers, which in turn allows you/us to determine any deterioration by means of a before/after comparison.

What none of us is able to predict is the use of new or more aggressive detergents that may be used in the future.

Methods of instrument marking – what are they?

We need to make clear at the outset that we are talking about marking Medical Devices. If you mark these instruments in a manner not approved by the manufacturer, any liability associated with the instruments performance may transfer to you. Obtaining such approval is difficult at best and we believe that the best approach is to use the least intrusive method that you are able to do.

Dot Peen - dot peen marking creates a dent or dimple in the surface of the material which stretches the surface layer, but does not break it. The integrity of the instrument is not affected by this process, but it does not create a high contrast mark. Reading of the code is dependent on the reflection of the light entering the dimples made being different to the light reflected from the unmarked instrument surface.

Laser Marking - is a process used to discolour the instrument surface layer substrate without burning, melting or vaporising the instrument material. This is done by passing a low power laser beam across a surface at low speed to discolour the area of the mark. This produces a high quality, high contrast mark that does not disrupt the surface. Properly applied, the mark cannot be felt when rubbed by the finger.

Laser Bonding - is an additive process that involves the bonding of an inert substance to the instrument surface. The patented bonding materials consist of ceramic and ground metal oxides mixed with organic pigments. The application is permanent and provides a darker mark than the laser colouration process. Because of the need to apply the bonding material, this process is slower, but the actual marking time is quicker.

Laser versus Dot Peen?

Laser markers normally provide a more precise mark than a dot peen marker. Since the precision of the mark is an important factor in machine readability, this results in better readability for laser marking in certain applications.

Dot peen marks are by nature low contrast marks, which depend solely on illumination techniques to create the contrast required for marking. On the other hand, in certain applications, laser marks produce higher contrast, which tends to add to their readability. The minimum size of a dot peen 16 x 16 element code is around 4 x 4 mm. By contrast, a laser code of the same structure can still be read with similar ease at half the size ( 2 x 2 mm).

Dot peen markers imprint a round dot; whereas a laser marker is capable of marking a square cell. This adds to the relative readability of laser marks in 2D applications, since a theoretically perfect 2D code is based on square cells.
Dot peen markers cost considerably less than laser markers.

A dot peen marker utilizes much smaller components than a laser marker, making it smaller and lighter.

A laser marker is almost always much faster than a dot peen marker. For instance, the time to imprint a 10x10 2D code with a dot peen marker is typically in the range of 2.5 - 5 seconds; with a laser it's more on the order of ½ second.

Dot peen marks are widely accepted by the aerospace industry for marking critical parts; laser markers are typically not. The cross-section of a dot peen "dimjple" (dot) has no sharp corners, only gentle curves, resulting in no significant stress concentration. Laser marking can adversely affect material properties in the heat-affected zone of the mark, which can potentially result in the propagation of cracks in certain materials.

Dot Peen – Can I hold the instruments to be marked manually?

You can, but you introduce the risk that a small unintentional movement will ruin the code. It is far better to firmly locate the instrument so that it cannot move during the marking process. You may also wish to consider the risk associated with holding vibrating instruments over an extended period of time.

Lasers – are they dangerous?

As with laser pointers or medical lasers they have the potential to be dangerous! They use relatively high levels of energy and will damage eyesight or can burn if you are exposed to their beams. The lasers should be used with the appropriate enclosures which prevent their use unless the door is securely closed and you should involve your Health and Safety Officer prior to purchase, rental or lease.

Lasers – do I need fume extraction?

It depends on your process. If you use a laser etching process where you remove material by burning you will have gaseous metals in your local environment. In this case fume extraction may/will be necessary. If you use laser marking or bonding, you are simply heating the surface and no fumes or material will get into the environment. To be on the safe site, you should consult your Health & Safety Officer.

Laser Bonding – Is it permanent and can the material come off in a patient or washing/sterilizing processes?

The material used is melted onto the surface of the instrument so that its presence is permanent. It is as strong as the instrument and cannot be removed without removing the instrument surface as well. Numerous test documents are available showing its permanency under a range of different and hostile test conditions, with different chemicals, at different temperatures etc.

Laser Bonding – Is the bonding material dangerous to use by operators?

Yes and no! Yes it does contain a hazardous material – crystalline silicate which is a known carcinogen! Before you get too concerned, crystalline silicate is another term for quartz, which is a major constituent of sand, which can cause health problems if inhaled in large quantities, as in the building trade for example. In the case of instrument marking, the amount present in the bonding material is minimal. If you were to make 1000 marks in a day, the total exposure level will be equivalent to just over 1 grain of sand which is well below the safe exposure limit. No PPE is required. In any event, the material is unlikely to be inhaled as it is either in a moist condition else in a stable dry condition.

When we carry out bonding, we always ensure that we clean marks and spillages using moist cloths to prevent the material becoming airborne and avoid any risk of inhalation.

Laser Bonding – Does it take longer?

Yes there are the additional processes of applying the ink and subsequently wiping it off after marking.

We speed this process by using our own ink application system which takes minimal time.

The benefit of the high contrast, readable mark makes the extra effort worthwhile.