During the 1960s, an engineer named Godfrey Hounsfield was developing a revolutionary new method for non-invasive body imaging: CAT scanning. CAT, now commonly called CT, scanners produce cross-sectional images that can be compiled to create three-dimensional representation of the inside of the body. This type of imaging is often used to check areas like the brain or stomach for damage, tumors, and other abnormalities. Computed tomography, or computerized axial tomography, is similar to magnetic resonance imaging (MRI), but where MRI machines use a magnetic field and radio waves (i.e. greater than 1 e-3 m), CT scanners use X-ray wavelengths (.1-10 e-9 m). MRI technology is not quite as old as that of CT, and tends to be the preferred method for routine scanning. However, CT scans are significantly less expensive to produce, and remain the better method for investigating brains post-stroke.

To recap, beginning in the early 1900s, doctors could use X-rays to produce two-dimensional radiographs that looked along the dorsoventral axis of a person’s body.  X-ray machines have a source, typically called a tube, that beams X-rays into the patient, and a detector that receives whatever comes out. The rays received by the detector are then translated into the radiograph. Rays that easily pass through the body, like those aimed at regions that consist primarily of tissue, experience very little change in energy and show up as grey on the radiograph (for reference, beams passing through air appear black). However, materials that can “stop” X-rays by absorbing some of their energy cause attenuation of the beams; in other words, the energy of the beam is reduced, causing what’s called a “remnant” beam to continue to the detector. In essence, the radiograph illustrates energy differences in a spectrum of black to white, mapping where each occurred in the body. The whitest parts of the radiograph correspond to the places that absorbed the most energy.  Without getting into a lot of chemistry, calcium is better at absorbing X-rays than carbon, which is why bones shine the brightest.

With a CT scanner, the x-ray tube rotates within the machine’s hoop frame, sending beams all throughout the body. The returning beams are sent to the computer, which interprets and compiles them. The “thickness” of each cross-sectional image can vary depending on the machine, but a standard slice is typically 1-10 millimeters. Even so, there remains the issue of different materials’ varied abilities to absorb energy. One solution is to use substances that contain X-ray-absorbing particles to highlight various areas or systems for the machine. For example, a patient might be given an oral agent containing barium so that their stomach will show up better in the images.

At a time when static X-rays were virtually the only method of viewing inside the body without physically entering, Hounsfield had the idea that it was possible to figure out what was inside a closed box by taking X-rays of the box at all angles. It became necessary to have a computer powerful enough to process the X-rays and reconstruct them into legible images at a rate fast enough to potentially save dying patients. While Hounsfield was developing his scanning technology, he was also an employee of Electric and Musical Industries, a company that was the child of the merge between The Gramophone Company and The Columbia Gramophone Company that took place in the ‘30s. EMI had already produced the first commercially available computer that ran on discrete transistors instead of vacuum tubes, a project for which Hounsfield had been a key developer.

In addition to developing computers and other electronic appliances, EMI was the parent company to multiple record labels and owned Abbey Road Studios. Abbey Road had been recording albums for big-name bands for decades and in the early ‘60s signed, you guessed it, the Beatles. EMI gave the Beatles unlimited time and access to its studios, allowing them to infamously experiment with their recording techniques and ultimately achieve striking sound quality. Coincidentally, their sound-intensive recordings required computing capability not unlike that which Hounsfield would need for scanning applications. The combination of the demand for faster machines, the enormous revenue coming in, and the plethora of EMI’s available resources made for the perfect storm for Hounsfield. CT scanning achieved viability in the ‘70s and won Hounsfield a Nobel prize.

Thank you to Tom Bacsanyi for inspiring this topic.

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