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Advanced medical & Biometric Imaging Part 2: By Dr David Maddison – Non-Medical Uses Now that we’ve covered many medical imaging techniques like X-ray, CT, PET, MRI and ultrasound, it’s time to cover other uses for these (and similar) technologies. There are surprisingly many applications outside the realm of healthcare. Image source © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons – https://w.wiki/3XDf) Y ou will be aware that X-rays are used for security purposes, such as at airports to check baggage and passengers for contraband and weapons. But these days, it isn’t just X-rays being used, and many of these imaging techniques are being used for other purposes, like archaeology, as we shall now describe. X-ray inspection When Röntgen discovered X-rays in 1895, he mentioned one possible use as detecting flaws in materials such as steam pressure vessels. They are still used for that purpose to this day – see Fig.49. One important electronics-related use of X-rays is the inspection of PCBs and solder joints, especially when solder joints are hidden, such as with BGA and LGA packages. X-ray inspection is a critical part of quality control for advanced electronics which make extensive use of BGA/LGA package devices – see Fig.50. Defects that can be detected by X-ray include breaks in tracks, voids in solder joints and missing or incorrectly-sized solder balls. Airport baggage and cargo Airport passenger luggage (and indeed all aircraft cargo) is always X-rayed to detect explosives or weapons (see Fig.51). X-ray machines have traditionally been of the planar type, with a single X-ray beam passing through the luggage. To give you some idea of the advances in security X-ray technology, the machine shown in Fig.51 offers optional proprietary iCMORE software algorithms to detect lithium batteries, as well as other hazardous or dangerous cargo such as flammable liquids or solids, and liquefied or compressed gases. We have probably all noticed the images on the security screener monitors as we have gone through X-ray security checkpoints at airports. But Fig.50: an X-ray of an assembled printed circuit board (PCB) with a ball-grid array (BGA) package IC at the centre, and vias and passive devices surrounding it. Not only can you see the PCB tracks, IC bond wires and BGA solder balls adhering to the lands and pads, but also the copper plating in the vias and the internal structure of the components to the left, which appear to be a resistor and possibly a fuse. Fig.49: X-ray inspection of a weld showing defects. Source: NTB (https://ntbxray.com). 14 Silicon Chip what do the colours mean? X-rays do not yield colour information, but they do provide information about the average atomic weight and thickness of the materials they pass through. Most X-rays will pass through materials with a low average atomic weight, such as plastics which include some combination of two or more atoms of carbon, hydrogen, nitrogen and oxygen. Materials that have much higher atomic weight metals such as steel and aluminium will comparatively absorb many X-rays. Similarly, the thicker or more dense something is, the more X-rays are absorbed and the lower the X-ray count through the material. With security X-ray machines, the X-ray image is artificially coloured according to a material’s overall atomic weight average (and density), which initially appears as grey levels. The software colourises the greyscale X-ray image, as the human eye can more readily distinguish colours Australia’s electronics magazine siliconchip.com.au than shades of grey. This aids the job of the security screener, providing a rough indication of what materials are present. A certain amount of interpretation is required, as a very thick layer of a low atomic weight organic material like a block of photocopy paper may appear the same as a thinner layer of a more dense metallic material. Typically, materials can be identified according to whether they are organic, metallic or a mixture of both, and some further distinctions within those categories. Within organic materials, it is usually possible to distinguish between harmless inert materials like clothing according to the substance’s mean atomic number and density. So it might be possible to distinguish between materials like plastics, explosives and illicit drugs. Lighter atomic number metals like aluminium can be distinguished from heavier atomic numbers like steel. Similarly, gunpowder can usually be identified. Gold and silver, which might be the subject of smuggling, can also be distinguished because of the very high atomic number of these metals. Human intuition, common sense and observation of a suspicious person are also parts of the detection process. Teledyne ICM (www.teledyneicm. com) is one company that makes various security products. They produce a system and software known as Flatscan for portable X-ray screening. Fig.52 shows a monochrome X-ray image produced with Teledyne’s Flatscan software, with no colour coding. Firearms, bullets and a laptop computer are clearly visible. Lighter areas represent substances of high atomic weight like metals, where few X-rays penetrate. Darker areas are lower atomic weight materials such as plastics, where many X-rays penetrate. In Fig.53, the image of Fig.52 has been colourised. The firearms are blue, suggesting they are very dense metal, not fake plastic toys. The green/blue square object indicates an item made of dense plastics and metal, like a laptop computer. In Fig.54, an image of a similar bag has been processed using Teledyne’s Flatscan software to reveal different materials according to their atomic weight. The non-organic materials or dense organic plastics are green, with siliconchip.com.au Fig.51: the Smiths Detection Group Ltd HI-SCAN 10080 XCT advanced CT explosives detection system for checked baggage and air cargo. The manufacturer states that it “features a dual-view dualenergy X-ray line scanner with full 3D volumetric computed tomography (CT) imaging and reconstruction”. 53 52 Fig.52 (above left): a ‘standard’ greyscale X-ray image of a bag that an airplane passenger might carry. Source: Teledyne ICM. Fig.53 (above right): a colourised version of Fig.52, showing different details. Source: Teledyne ICM. 54 Fig.54 (lower right): this false-colour X-ray image shows organic materials in orange and inorganic in green, with the inorganic materials mostly removed. Source: Teledyne ICM. Z-Number Material Type 3 Color 6 Color Examples Possible Threats 0-8 Organic Orange Brown Wood, Oil C-4, TNT, Semtex 8-10 Low Inorganic Orange Orange Paper Cocaine, Heroin 10-12 High Inorganic Green Yellow Glass Propellants 12-17 Light Metals Green Green Aluminium, Silicon Gunpowder, Trigger Devices 17-29 Heavy Metals Blue Blue Iron, Steel Guns, Bullets, Knives 29+ Dense Metals Blue Violet Gold, Silver High Value Contraband – Impenetrable Black Black Lead Shielding for above threats Fig.55: an X-ray colour-coding scheme from Totalpost Mailing Ltd, showing the atomic number range (Z) in the left column and examples of possible threats that might be represented. Different software manufacturers may use different colour coding. These colours do not apply to Figs.52-54. Australia’s electronics magazine September 2021  15 lighter organic materials represented by orange. Note the orange object (a light organic material) at the bottom with what appears to be green nails in it, suggestive of a bomb; this might not be readily visible without this sort of high-contrast colouring scheme. Fig.55 shows one possible colour coding scheme for this type of false-colour image. This is not necessarily consistent between X-ray devices or manufacturers. Backscatter X-rays for airport screening Fig.56: typical backscattered X-ray images from an airport security scanner showing no weapons detected. Some systems have software that covers private body parts. Source: US Transportation Security Administration (TSA). Fig.57: the Tek 84 Defender airport body scanner. It uses software to provide automated threat detection (ATD). When threats are detected, they are placed on a cartoon figure representation of the body. It uses backscattered X-rays and detects both metallic and non-metallic threats. Source: Tek 84. Fig.58: the Z Portal from Rapiscan AS&E (www.rapiscan-ase. com) for trucks and cargo. It provides high-throughput backscattered X-ray imaging of large trucks, buses and shipping containers. It can process up to 250 trucks per hour. The X-ray systems discussed above operate in transmission mode. The X-rays have to penetrate the target and be detected by a sensor of some kind. With backscattered X-rays, some of the X-rays directed at the target are instead reflected back toward the X-ray source by a process called Compton scattering. One of the main applications for backscattered X-rays is full-body scanning in airport security systems to detect weapons (see Figs.56 & 57). Very low doses of X-rays are used, about one-thousandth that of a chest X-ray. These are not considered harmful, although not all agree with that claim. A controversial aspect of backscattered X-ray imaging is that it can produce high-resolution imagery of a person’s body beneath their clothes. Therefore, software often covers or distorts a person’s private parts, and the screening agent looking at the image may be physically separate from the person being scanned. X-rays of shipping containers and trucks X-rays of shipping containers and trucks have become routine for security purposes and the unavoidable: taxation! See Figs.58, 59 & 60. These scanners provide high-resolution images. The X-rays are generated with the aid of a linear accelerator. Either regular transmission or backscattered X-rays can be used – backscattered X-rays have the advantage of being less harmful to people, and can be used if only one side of the object is available for inspection. Handheld backscattered X-ray imaging system These devices are suitable for 16 Silicon Chip Australia’s electronics magazine siliconchip.com.au inspection applications like vehicles, house walls, aircraft interiors, packages etc. They are handy when away from stationary inspection systems (see Figs.61 & 62). CT scanning of the Antikythera Mechanism The Antikythera Mechanism is an extraordinarily complicated 2000+ year-old mechanism (Fig.63), recovered from a shipwreck by fishermen around 1900. It had become a heavily corroded, calcified mass that has been intensively studied. It was too fragile and corroded to disassemble, so it was originally X-rayed and has most recently has been subjected to CT scanning, to try to understand how it was made and what it did. This revealed some hereto unknown or undecipherable engravings (see Figs.64 & 65). All the evidence points to it being a type of mechanical orrery for predicting orbital positions and eclipses. See the video titled “Scientists Have Just Fully Recreated The Design Of The Antikythera Mechanism For The First Time” at https://youtu.be/ E8YUxuz1uZQ An Australian YouTuber called Chris has reconstructed the tools the Ancient Greeks would have had, then used those tools and techniques to reproduce the mechanism. See his videos playlist at siliconchip.com. au/link/ab98 The industrial CT machine used to scan the Antikythera Mechanism was a prototype by X-Tek Systems called Bladerunner (Fig.66), operating at 450kV. X-Tek is now Nikon Fig.63: the mass of one of the fragments of the Antikythera Mechanism. It can’t be prised apart without destruction, so it is investigated via non-destructive means. Source: Wikimedia user Marsyas. siliconchip.com.au Fig.59: a backscatter X-ray image of a truck showing a dummy ‘hiding’ inside. This was taken by a ZBV system manufactured by Rapiscan AS&E (www. rapiscan-ase.com). Source: www.proammo.cz/x-rays/ Rifle Propane Tank Drugs Fig.60: an image from the Z Backscatter system from Rapiscan Systems AS&E. The backscatter X-ray of the suspect vehicle on the left reveals organic items like drugs, while the transmission X-ray on the right reveals metallic objects. Source: Rapiscan. Fig.61: the handheld MINI Z backscattered X-ray inspection system from Rapiscan Systems / AS&E. Fig.62: concealed items inside a car tyre are revealed with a MINI Z scanner. Fig.64: a computer reconstruction and exploded view of the Antikythera Mechanism. Source: Nikon Australia’s electronics magazine September 2021  17 Metrology, and they offer a 450kV machine called XT H 450 X-ray and CT system with a unique 450kV microfocus X-ray source. This gives 25 micron (0.025mm) repeatability and accuracy. The Dead Sea Scrolls Fig.65: a CT reconstruction of the engravings on the Antikythera Mechanism from within the encrusted, corroded mass. PTM stands for polynomial texture mapping. CT imaging enabled unambiguous interpretation of previous results (A vs B and C vs D, unknowns in squares). Source: Plos One (siliconchip.com. au/link/ab9e) Fig.66: the X-Tek, now Nikon Metrology XT H 450 X-ray and CT machine for high-resolution non-medical X-ray imaging and CT scanning. A similar device was used to scan the Antikythera Mechanism. The Dead Sea Scrolls were one of the world’s most spectacular archeological finds. They were found in Israel in the later 1940s and early 1950s, consisting primarily of ancient biblical scrolls about 2000 years old. They were mostly written on parchment; some had become illegible due to age and damage, while others were so damaged and brittle they could not be unwrapped. Advanced methods were required to read both some of the parchment, papyrus and even copper scrolls. Some otherwise unreadable parchment was read using the process of multispectral imaging (see Fig.67). This relies on the fact that the reflectance of ink and paper are much different with non-visible wavelengths of light such as infrared. The remarkable difference between the visible light image and the infrared image can be clearly seen in the figure. The so-called En-Gedi scroll was very badly damaged, brittle and very little more than a chunk of burned charcoal. It could not be unwrapped as it would disintegrate. Archeologists therefore ‘shelved’ it for many years, waiting until technology could help view its contents. In 2016, it was imaged with a micro-CT scanner by a team at the University of Kentucky, Hebrew University of Jerusalem and the Israel Antiquities Authority – see Fig.68. Also see the video titled “Virtually Unwrapping the En-Gedi Scroll (English)” at https:// youtu.be/GduCExxB0vw The ink was iron- or lead-based and so gave a contrast difference in the imagery. After scanning, clever mathematical techniques were applied to ‘virtually unwrap’ the scroll and read the text – see siliconchip.com. au/link/ab99 The team that deciphered the En-Gedi scroll is now looking at using radiation from a synchrotron to read certain scrolls at an even higher resolution than these CT scans. A giant CT scanner The Fraunhofer Institute for 18 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.67: a fragment of Biblical text on parchment, invisible to the naked eye, is clearly revealed under infrared light. Source: Israel Antiquities Authority. Integrated Circuits IIS in Germany (www.iis.fraunhofer.de/en.html) has developed a giant CT scanner for scanning objects such as cars, shipping containers or aircraft parts. The system is known as high-energy CT or XXL-CT (see Fig.69). The X-ray beams used are up to 9MeV to provide high penetration levels and suitable imaging density and resolution in the sub-millimetre range (Fig.70). The main components are a linear accelerator to produce X-rays, a 4m wide X-ray detector for line-by-line scanning, and a turntable to rotate the object being scanned. A scan can take up to 100 hours and produce terabytes of data to analyse. Applications include: • material analysis such as the detection of defects in castings or composite layups down to 0.2mm • checking the assembly of various components to make sure all parts have been assembled correctly (including the location of welds and adhesives, cable layouts and that no parts have been omitted) • analysis of failed components • examination of crashed vehicles and comparison with simulations • examination of objects for hidden contraband • digitisation of objects of significant cultural heritage (eg, so that a destroyed statue could be reproduced) Other uses for CT scanners Apart from archeological investigations and engineering inspections, industrial CT has a multitude of other uses. Among these are looking at the distribution of crystals or cavities inside rock samples, examining embedded or exposed fossils (Fig.71), studying meteorites etc. CT scanners are also siliconchip.com.au Fig.68: the En-Gedi scroll was extremely damaged, almost a lump of charcoal (see the image on the right). It was scanned using a micro-CT scanner and “unwrapped” with software, as shown on the left. Source: University of Kentucky. Fig.69: the Fraunhofer XXL-CT system. The main components are a linear accelerator on the left to produce X-rays, a four-metre-wide X-ray detector on the right for line-by-line scanning, and a turntable to rotate the object being scanned. The object in the middle at the back is an alternative detector and specimen manipulation system. Source: Fraunhofer IIS. Fig.70: a CT image of a car made with the Fraunhofer XXL-CT machine. Fig.71: an unusual patient. This is a 3D CT reconstruction of the skull of a Herrerasaurus dinosaur with a cutaway showing the braincase. The sample is 32cm long. Source: Carleton University. Australia’s electronics magazine September 2021  19 Fig.72: the Rapiscan 920CT airport CT hand baggage scanner. Fig.73: the primary sequence of an iris recognition scheme. used for airport hand-luggage security screening (Fig.72). See the Youtube video titled “920CT - SEE INSIDE THE FUTURE - Checkpoint CT” at https://youtu.be/ PFOEQKqNOFE Eye scans for biometric security Biometric imaging of the eye is increasingly important for security purposes. The iris or pattern of blood vessels of the retina or sclera can be scanned. The retina is the lightsensitive part at the back part of the eye, while the iris is the coloured part, the sclera is the white part of the eye. Like a fingerprint, the eye has many unique characteristics for each individual, even identical twins. The retina has a unique pattern of veins that remain stable throughout life and are not prone to damage like fingerprints (although they can change somewhat due to various diseases). These can be harmlessly imaged 20 Silicon Chip using infrared light. Once an image is acquired, the software checks whether the scan matches the stored image of an authorised person. One disadvantage of the technology is the relative difficulty of quickly acquiring a sufficiently high-quality image, and cataracts or glaucoma can render the technology unusable for an affected individual. Retinal scanning is currently not the preferred method of eye scanning due to these difficulties. The pattern of the iris is highly individual. While a fingerprint has 60-70 points of comparison, an iris has about 260. It is currently the preferred eyebased biometric security measure over retinal scanning (see Fig.73). Iris recognition works by first taking a snapshot of the iris with a camera 10-100cm away, using infrared light, which copes better with all iris colours. Once an eye image is acquired, the image is processed, with concentric circles around the iris forming a polar Australia’s electronics magazine Fig.74: this is the optical fingerprint scanner module that we used in our November 2015 access control project. More advanced (and complicated) schemes can be used for higher security. coordinate system. These coordinates are then transformed into a rectangular coordinates to create a strip image which is then analysed. The computer converts this image to an “iris code”, which is a 512-digit number used to compare with reference images. As for fooling the system with cosmetic contact lenses, these can be detected because they have different reflective characteristics. Systems are also in place to detect a living person’s natural, involuntary eye movements, plus the pupil expansion is checked. However, some commercial scanners without these precautions have been fooled using high-resolution pictures of a person’s eye. Iris scanning is often confused with retinal scanning, but iris scanning is much more common. Another method under development is scanning the blood vessels of the sclera. It has the advantages of rapid image acquisition with standard cameras, without needing infrared light. Facial recognition Facial recognition is used by smartphones, social media, governments, militaries and police agencies. This was the subject of an article in Silicon Chip, April 2019: “Big Brother IS watching you: Facial Recognition!” (siliconchip.com.au/Article/11519). See that article for further information on this topic. Fingerprint scanning Many phones and other systems use siliconchip.com.au Fig.75: how two radiation sources would appear if stored in an enclosed container and imaged with an NGET machine. fingerprint scanning for access control. These can be based on optical, capacitive, ultrasound or thermal technology. The fingerprint is first scanned by one of these methods, then the distinguishing features of the fingerprint are extracted and matched to a database. We published a DIY project to build a fingerprint-based door access controller in the November 2015 issue (siliconchip.com.au/Article/9393). That design used an optical fingerprint scanning module – see Fig.74. Neutron-Gamma Emission Tomography (NGET) NGET is a technology under development at the KTH Royal Institute of Technology in Sweden to pinpoint the source of nuclear materials that could be used for terrorism, such as weapons-grade plutonium or materials that could be used to make a “dirty bomb”. It is a form of tomography for nuclear materials – see Fig.75. Fig.76: the Leidos ProVision 2 is a millimetre-wave scanner for aviation security use. It features automatic target detection, and only shows a cartoon-style image of the location of any detected items. It is designed to process 200-300 people per hour. Source: Leidos (www.leidos.com). Millimeter-wave imaging Millimetre waves are radio waves with a frequency around 30-300GHz. Millimetre-wave whole-body imaging scanners illuminate the body with low-power millimetre RF waves and detect the reflected radiation – see Fig.76. Unlike X-rays, millimetre waves are a form of non-ionising radiation, and are claimed to be safer than backscattered X-ray scanning. Millimetre-wave scanners may be active or passive. Active systems generate the radio waves themselves and measure the reflected radiation, while passive systems produce images from siliconchip.com.au Fig.77: the operating principle of ultrasonic material testing. An extra reflection corresponding to a hidden defect results in an addition to the expected reflections from the front and back surfaces. Ep relates to the depth of the piece, while D relates to the defect depth. Source: Romary. Australia’s electronics magazine September 2021  21 Fig.78: the general scheme of an acoustic emission system. With multiple transducers, the location of the crack or other defect can be determined. Source: Khodadadi and Khodaii, 2018. the millimetre waves naturally found in the environment. As with X-ray backscatter scanners, many such machines use software to disguise the body image and produce only a generic cartoon-like outline of the body showing the location of suspicious objects. See the video titled “ProVision 2 - Compact Advanced Personnel Screening” at https://youtu.be/ O6HxV807f5A Ultrasonic flaw detection Ultrasonics can be used to detect flaws in mission-critical components such as aircraft parts. An ultrasonic wave is sent into one side of the test piece, and if an internal flaw is present, there is a reflection from it as well as the far side of the piece. If no flaw is present, there is only the expected reflection from the far side – see Fig.77. Acoustic emission Acoustic emission is the phenomenon whereby crack growth processes in a material generate acoustic energy. This typically occurs in response to mechanical loading of the material. By instrumenting an item under test, the location of a propagating crack can be determined, or the overall structural health of an object under continuous monitoring can be determined (see Fig.78). Acoustic waves generated by the cracking process are typically in the range of 100kHz to 1MHz. A computer can process signals from multiple acoustic sensors to determine the location of a growing defect such as a 22 Silicon Chip crack, eg, by triangulation. This process cannot detect defects that aren’t growing. Acoustic emission testing is typically used on: • concrete structures like bridges • metallic structures like pressure vessels, pipelines, aircraft structures and steel cables • composite structures such as used in aircraft and racing cars, and structural composite beams • rotating machines, to detect bearing wear in machinery • electrical machinery like transformers, to establish if there are unwanted electrical discharges taking place • leak detection in pipes Borescopes Borescopes are the non-medical equivalent of endoscopes and are used to inspect inside engines, machinery, walls or ceilings, pipes, security inspections, inside gun barrels, or anywhere else where disassembly of an item is impractical, expensive or impossible – see Fig.79. They may be rigid or flexible. Low-cost borescopes can be purchased on eBay or from some retailers, and many of them connect to the USB port of a computer or a phone. We have even seen some for sale that suit Android phones for less than $10, while some more expensive modules work over WiFi. We have tried some slightly more expensive models (around $30) and found them to work very well for tasks like checking inside ceiling cavities through downlight openings. Australia’s electronics magazine Other Silicon Chip articles Apart from those articles already mentioned above, you might be interested to read the following sections of past articles which touch on this topic: • The Range-R through-wall scanner described in the article “History of Cyber Espionage... Part 2” (October 2019; siliconchip.com. au/Article/12013). • Ground-penetrating radar from the article “Underground mapping... & pipe inspection” (February 2020; siliconchip.com.au/ Article/12334). • Seismic surveys in the article “Directional Drilling: How It Works” (July 2016; siliconchip. SC com.au/Article/9997). Fig.79: the PCE-VE 270HR industrial-grade borescope from PCE Instruments (www.pce-instruments. com/english). It has a two-metre-long flexible cable, 2.8mm in diameter. siliconchip.com.au