Observant visitors to the X-ray department at Dunedin Hospital may have noticed a framed photo on the wall, showing an X-ray of a hand. Those who were sufficiently intrigued to learn more might have read the legend, and would have discovered that this was a historic photo, from 1899, the work of Dr Henry de Lautour, medical practitioner of Dunedin, who had introduced X-rays to New Zealand only eight months after Dr Roentgen’s original discovery in 1895.
Back then, we really were up with the play. There, in the 19th century, they could see the bones of the hand, and of itself, through 21st century eyes, an unremarkable illustration. Then, however, this was utterly stunning. Actual bones, in a living person, actually visible. It is hard to overstate what an extraordinary development, in the history of medicine this was.
Back in the somewhat more recent 1970s, another remarkable development took place, but similarly, these days, rather taken for granted. This was CAT scanning, which subsequently (for a technical reason) changed its name to CT scanning. Now, several organs which had formerly been seen on standard X-ray as vague, indiscernible differences in grey, could be well distinguished. This writer recalls, while on an attachment at the University of Iowa Hospital in the early 1980s, being amazed at a particular variation of this technology, "gated CT": the scanner was primed to take images in time with the heartbeat of the patient, and so the anatomy of the valves of the heart, in life, could very precisely be captured.
The next wonder was MRI. It was known, at first, as NMR (nuclear magnetic resonance); but it was thought the word "nuclear" might put some people off, and so it changed to magnetic resonance imaging. It has particularly been in the examination of the brain — the most complex structure in the known universe — that MRI scanning has shone. So many brain diseases, such as multiple sclerosis, are so much better understood these days because of the insights MRI has enabled.
Alongside these methodologies based upon electromagnetic radiation, has been ultrasound, bouncing back sound waves, evolving in part out of submariners’ requirements in the 1950s to latter-day medical applications, notably in cardiology and in foetal medicine.
As well as the anatomy, "functional" forms of these various scans, mostly based on detecting differences in blood flow or in metabolic activity, could give a more subtle insight into what might be going wrong in the body.
And then we come to PET. PET, another acronym: positron emission tomography. This was a quantum leap from CT and MRI. PET scanning differs in that it uses a very low dose "radioactive tracer" to home in, with extraordinary precision within a millimetre or so on to a particular target tissue. And especially, with cancer as the target. Cancer cells are more active, and PET can detect this.
PET scanning isn’t new. Hundreds of hospitals around the world have PET scanners. But its applications continue to evolve. At present, several different cancers are amenable to PET scanning, and one in which PET is making a particular mark is prostate cancer. The standard of care now, in many countries, is for PET to be offered for certain categories of prostate cancer, when standard therapies have failed.
The PET approach to prostate cancer is brilliant, in its elegant simplicity. Many prostate cancers produce a distinct marker on the surface of the cells that make up the tumour: the fancy name for this signature marker is PSMA, Prostate Surface Membrane Antigen. A flag, as it were, that says "here be cancer". Medical physicists tailor-make a molecule in the laboratory that matches PSMA, and attach to this a radio-label. The molecule is injected into a vein, it homes in on the cancer cells, and the PET scanner identifies them. This is typically combined with a CT scan, to give an overall picture of where the cancer actually is: this is PET/CT scanning.
And then, if the picture is suitable, and employing the so-called "theranostic" (therapeutic + diagnostic) approach, another tailored molecule can be injected, this time with carrying an isotope that emits very localised "beta" radiation; the isotope of choice in prostate cancer is Lutetium-177. The molecule attaches to the cancer cells, and the beta radiation affects only this targeted tissue, killing the cancer, and avoiding normal tissues: an exquisitely precise therapy, that can sidestep the usual side effects of standard radiotherapy.
The before-and-after PET scans can be stunning: the cancer seems to have melted away. Our colleagues in Melbourne, at the Peter MacCallum Cancer Hospital, are world leaders.
It would be good to have this facility available in our new hospital. As more cancers come to be better understood and managed through PET, we could, once again, be up with the play.
Those who developed these imaging techniques were very clever scientists, and Nobel Prizes have been awarded to the discoverers of X-rays, CT, and MRI. PET discoverers are slated to be the next up; the prize, when it happens, will be richly deserved.
- Mac Gardner is a retired medical geneticist. He intends to stand as an independent candidate in the upcoming general election.
