X-Ray imaging - The Gendex GXS-700 X-Ray dental imaging array.

[Fraser]

As those who have been following my X-Ray images thread will know, I have purchased a Gendex GXS-700 dental X-Ray imaging sensor that is in need of repair. Well it arrived from the USA today.

These sensors are used in place of dental X--Ray film and are composed of an electronics package that converts X-Ray energy into images that are passed to the host PC via USB. The Gendex GXS-700 is actually a re-badged DEXIS Platinum sensor. The design is advanced in that all of the electronics are located in the head and USB plug, with no need for a large module that normally sits between the two. It is a highly integrated electronics package.

So how does it work ?

In the head you will find a scintillation plate that produces light when illuminated by X-Ray energy. Behind this there is a special fibre optic micro-channel plate to control light dispersion. The micro-channel plate passes the collected light to the CMOS imaging sensor. This is a physically large CMOS imaging sensor that is similar to that found in conventional digital cameras such as a Digital SLR. The CMOS imaging sensor converts the light into a voltage that may be read out by the support electronics and passed to the analogue to digital converters. The digital signal is then passed to processing electronics, and then to the USB interface.

The software on the Host PC processes the image information and presents it to the user for viewing and manipulation.

The sensor head detects when X-Ray energy is present and triggers its capture electronics to start the image exposure. The exposure is automatically stopped when the required ADU target has been achieved. The user does not need to setup the exposure, just the X-Ray Generator output duration, as with a film exposure. Very simple.

These sensors have a hard life and failure is common. They are in daily use and rely on a fragile umbilical cable. The actual head electronics are quite robust and the case is hermetically sealed against fluid ingress. The regular flexing of the cable tends to lead to failure, even if a cable protector sleeve is used. The companies that provide these imaging sensors usually offer service plans that repair or replace the sensors whenever they fail, which is often. As a result the support contracts are expensive. For Gendex it is $4000 per year ! Some owners elect to scrap older sensors as a result. Hence my purchase of a faulty one.

The GX-700 sensor that I have is the larger Size 2 and that normally retails at around $7000  Used ones sell for anywhere between $1200 (ebay) to $4000 (OEM refurbished).

These sensors are NOT the easiest items to repair. The head electronics are a total nightmare to work on and opening the head case tends to ruin the hermetic seal making them unsuitable for dental use. For hobby applications a 'compromised' head is still usable however.

The sensor is capable of producing high resolution images, albeit small ones, of PCB's and components. This is the use that I have in mind for my unit, if I can repair it (which is by no means certain)

Upon receiving my GXS-700, I was pleased to see physical damage to the USB connector. Why was I pleased? Well physical damage to such a connector is usually repairable and far less serious than a failure in the head electronics. The USB plug has been crushed and bent. This commonly occurs when a draw is closed on the plug or a wheeled chair driven over it  Yes people do ruin $7000 sensors through carelessness 

I shall X-Ray my sensor head, cable and USB plug to see if anything obvious is visible before I dismantle the required parts.

I will update this thread as I progress with the investigation. I am very busy at the moment, but watch this space 

Finally, a warning to potential purchasers of these types of imaging sensors...... they can suffer all manner of failures, plugs, cables, electronics and also firmware corruption. It is not unknown for sensors to be scrapped as they are beyond economic repair, which considering their value is surprising. Firmware corruption is not uncommon and requires the OEM's bespoke configuration and programming software. Not something they share with anyone except a service agent. Buyer beware. It is very easy to waste your money on these units.

On the software front, Gendex kindly provide some driver software on their web site for free download. Users will need the essential unique Calibration and defect file that accompanies their sensor though. A sensor without a calibration file is effectively useless as the software will not run without such being present (serial number locked).

Fraser

[Mashpriborintorg]

I have already played with similar sensors at work, Kodak brand, but exact same pricetag. I guess they are stupidly overpriced....

[Melt-O-Tronic]

Another awesome follow-worthy thread!         

[mikeselectricstuff]

 A long time ago I picked up an old dental sensor - surprised to see nothing inside but a huge slab of silicon and a scintillator - not even so much as a decoupling cap.
The only descrenable text on the die says "SUNI" and 1997
You can see why these things are so expensive though with a lump of silicon that big (27x38mm)
I gather that larger/(later?) ones use a process similar to TFT LCDs to make the large area sensors.

[Fraser]

@Mike,

That sensor head is the earlier type that uses a separate 'Dongle' interface to process the raw output from the imaging array. Those systems tend to suffer cable failures as the copper conductors are very thin to allow the use of a thin cable. The USB versions only have 4 conductors so can use slightly larger cross section copper cables.

The processing electronics that normally reside in the processing 'dongle' have been crammed into the Gendex head. Hence my comment on the high level of integration used. The down side of this is the challenge of repairing such miniaturised electronics and the need to open the hermetically sealed head housing, as opposed to a normal dongle housing that is screwed together.

The anatomy of the Gendex/Dexis imaging head is detailed here:

http://www.dexis.com/sensor-anatomy

In the attached image the layers are as follows (top down)

1. Front cover
2. Scintillator plate
3. Fibre optic micro-channel plate
4. Large CMOS detector array
5. Read-out and processing electronics
6. Rear cover with integral X-Ray attenuator
7. 4 conductor screened cable exits rear of sensor case via a small bulge.

Fraser

[KE5FX]

Interesting summary, thanks.  I actually bought a couple of these broken sensors recently (one adult-size and one child-size).  They are currently in the junk box awaiting some time to investigate repairing them.

Firmware corruption is not uncommon and requires the OEM's bespoke configuration and programming software. Not something they share with anyone except a service agent. Buyer beware. It is very easy to waste your money on these units.

I did notice that someone has reverse-engineered the 8051 firmware for the Cypress USB chip in these sensors (https://github.com/JohnDMcMaster/uvscada/tree/master/gxs700), or at least captured it for replay.  This should go a long way toward removing the dependence on the Gendex calibration files and/or proprietary software.  While I don't currently have much X-ray experience, I do have a good working knowledge of that particular chip, and I also have a friend in the area with wire-bonding and hybrid repair capabilities.  It's unlikely that anything could possibly go wrong with these things that we couldn't handle, given enough time to play with them... but that's the catch, as usual.   If you're able to post some detailed X-ray images of these things, it will help immensely if/when I have to open them up.

[Fraser]

For those readers wondering how good the images produced are when using these X-Ray sensor heads. I attach an image grabbed form a Dexis platinum ebay auction (not my sensor head but the same model).

Not bad quality.

Sensor head size 31mm x 42mm
True resolution is 1324 x 1842 pixels (with corners cut off)
Scintillator is Csl
Pixel size is 19.5um
Total pixels 2.4MP

Fraser

[Fraser]

@KE5FX,

Good to hear that you have some of these units as well.

For info, I have the OEM firmware reprogramming software used by the service agents when the unit suffers serial number corruption 

I have reshaped the USB plug and plugged it into my laptop. The good news is that the laptop now sees the sensor. I will need to install the driver software to test it further.

Fraser

[tautech]

Hell, need to subscribe to this thread too.

Thanks Fraser for sharing all these goodies.

[tautech]

For those readers wondering how good the images produced are when using these X-Ray sensor heads. I attach an image grabbed form a Dexis platinum ebay auction (not my sensor head but the same model).

Not bad quality.

Sensor head size 31mm x 42mm
True resolution is 1324 x 1842 pixels (with corners cut off)
Scintillator is Csl
Pixel size is 19.5um
Total pixels 2.4MP

Fraser

Would the SMD components that seem missing be ceramic caps and those seen resistors? (top right)

[Fraser]

Hi Tautech,

As you likely know, it is the density of the SMD component substrate that dictates the level of transparency when imaged using X-Rays. In my experience SMD resistors are normally pretty opaque when using lower levels of KVP on the tube. You can see through them by increasing the kVp and adjusting the ADU viewing window in the SR software. Common SMD capacitors do appear more transparent when imaged at the same KVP but I do advise caution. Not all capacitor types will appear the same. Tantalum's come to mind as they have higher density and it is possible to mistake an SMD ferrite for a resistor if you are not careful.

X-Ray imaging can be very useful in reverse engineering work as you can image the DUT and decide how best to proceed without causing damage to the PCB or components. Sadly X-Ray imaging is not very helpful when it comes s to identifying component characteristics. Visual inspection and component analysis is still needed.

Where an X-Ray image might excellent us in the disassembly or repair of a potted package or even an IC. Take for example a very rare Dallas RTC with internal potted battery that coming to the end of its life. The X-Ray would show exactly where to drill or cut in order to intercept the battery connections without damaging the electronics package. Very useful and a task I have carried out on several occasions using an X-Ray to guide me.

Fraser

[Fraser]

Mr McMaster is a clever chap.

There might be something of interest for you on this page Mike. He built a linear stage X-Ray scanner

http://uvicrec.blogspot.co.uk

At the bottom of the page you will see that he has released an independent GX-700 driver. Job done. Sweet.

Fraser

[Fraser]

Just for interest, the following page shows the many different models of Dental X-Ray sensor that are available.

http://dentalproducts.dentalproductsreport.com/s/dental-digital-radiography/products/filter/?category=dental-digital-x-ray-sensors

Fraser

[Fraser]

This is a good site that discusses the sensors and there is even an article on common hardware faults.

http://sodiumdental.com/digital-x-ray-review-part-1/

http://sodiumdental.com/category/sensor-repair/

Fraser

[marshallh]

Mr McMaster is a clever chap.

There might be something of interest for you on this page Mike. He built a linear stage X-Ray scanner

http://uvicrec.blogspot.co.uk

At the bottom of the page you will see that he has released an independent GX-700 driver. Job done. Sweet.

Fraser

Yup, he is. I gave a presentation with him this summer in Canada about chip decapping. If you are ever in the States you should see about visiting his garage of doom

[Fraser]

Very little time to 'play' with the GXS-700 but after reshaping the USB connector I have been able to get the sensor recognised and its firmware revision listed in the GXpicture driver. This is a good start as it suggests the USB comms channel and firmware in the head are OK. I will need to find a way to activate a capture mode in order to test the unit with live X-Ray but that will need to wait until another day. I have already loaded a trial version of the Gendex Twain interface so should be able to use that with generic capture software.

Pictures of GXpicture windows attached. It is just a driver interface and has no capture capability that I can find. The Gendex status indicator (top left corner of status box screen grab) is GREEN indicating that the sensor is ready to take an image and no problems have been found. The fact that the serial number is being shown indicates that the Calibration file is the correct one for the sensor    I wasn't sure that such would be the case or whether the serial number in the head would be corrupted.

It may be wishful thinking but the fault with this unit could just have been a damaged connector ? We shall see.

Fraser

[Macbeth]

Interesting. I take it you require an external xray source with these? They act like the old fashioned film plates the dentist shoves in your mouth before placing the xray device near your cheek then leaving the room and zapping you?

[Fraser]

Yes this is just the detector side of the system. A source of X-Ray energy is needed to illuminate the sensor array. The spec states a 60 to 70 KVp dental X-Ray generator. I have a Gendex 65kVp X-Ray generator so should have the required beam intensity for this sensor.

Fraser

[amyk]

Are we going to see some pictures of your teeth soon?

[Macbeth]

Are we going to see some pictures of your teeth soon?

Ooh, you don't want that... after all he's British (and ex secret service!) 

[tautech]

Are we going to see some pictures of your teeth soon?

Ooh, you don't want that... after all he's British (and ex secret service!) 

Nice one Macbeth. 
Real goood first laugh of the morning. 

[SeanB]

So they wil look like an old picket fence then?

[Fraser]

The Gendex GXS-700 contains a metal X-Ray scatter shield behind the PCB so I was not expecting it to be possible to image the PCB using my low energy Faxitron units. With this in mind I did some searching to see if anyone had tried to X-Ray the sensor with higher powered sources. I struck lucky.......

http://xrayfilmvsdigital.com/wp-content/uploads/2015/03/Dental-XRay-Radiography-study-s.pdf

I have extracted the image from the document. Not a great deal to see but the X-Ray does show some BGA footprints and the cable connections etc. The scatter shield is not that effective against X-Ray penetration, as noted in the document.

Fraser

[cex]

Mr McMaster kindly provided teardown images at SilconPr0n:

http://siliconpr0n.org/wiki/doku.php?id=gendex:gxs700

You may find these useful.

Also the API of his Linux driver allows triggering image sensor without X-rays that may also be useful to check if electronics are OK.

Regards,
Cex.

[Fraser]

@Cex,

Many thanks for the information, much appreciated.

Fraser