But the technology that makes them so valuable in diagnosing cancer and other diseases doesn’t have to be either huge in size or cost.
In a recent post on the technology website Gizmag, Brian Dodson describes a handheld Diagnostic Magnetic Resonance device developed by a team of physicians and scientists led by Prof. Ralph Weissleder of Massachusetts General Hospital: a device so sensitive that it can diagnose cancer with a greater accuracy than the current gold standard in a tissue sample far smaller (and far less painful to obtain) than that required by existing techniques.
Large-scale MRI machines work because human beings are largely made up of water. Each water molecule consists of two hydrogen atoms and one oxygen atom, and the nucleus of each hydrogen atom consists of a single proton.
Each proton is a little bit like a spinning planet Earth, with a north pole and a south pole. Under normal circumstances, the axes of all these little spinning protons are randomly aligned. But an MRI machine contains extremely powerful magnets, strong enough to cause most of the protons’ axes to line up with the magnetic lines of force within the machine.
When additional energy (provided by a radio wave) is added to the magnetic field, all these little protons resonate. Switching off the radio wave causes the protons to return to their resting state and release the energy they’d absorbed from the electromagnetic pulse as a radio signal that can be detected and used to create an image.
Since different tissues relax at different rates when the signal is switched off, different radio frequencies can be used to emphasize different tissues or abnormalities. An MRI scan is therefore typically made up of a series of pulse sequences, emphasizing different things.
Prof. Weissleder’s handheld Diagnostic Magnetic Resonance device works essentially the same way. The world’s smallest cancer diagnostic system, and one of the smallest magnetic resonance devices ever developed, it obviously doesn’t have a huge superconducting magnet: instead, it contains a permanent magnet just eight centimetres in diameter and 5.5 centimetres tall, providing a 1.2 cm region of constant magnetic field. Although just 0.5 Tesla (compared to the 1.5 to 3 Tesla fields in most MRI machines), it’s still 10,000 times the strength of the Earth’s magnetic field.
Since the device isn’t designed for examining an entire body, it doesn’t rely on resonating hydrogen nuclei. Instead, samples are mixed with tiny magnetic particles to which are attached antibodies targeted for specific cellular markers of cancer. The antibodies attach to sites in the cell membranes expressing that cancer marker. Just like the protons in water molecules in the body in the full-size MRI machine, the magnetic particles line up with the magnetic field inside the DMR device, resonate when a radio signal is pulsed through them, and then emit an echoing signal as they relax, which can be detected and indicates the presence of a particular cancer marker in the biopsy sample.
The research team discovered that it took a diagnostic panel of several cancer markers to obtain a clear diagnosis of cancer. They used material from 50 cancer patients, looking for any of a set of 12 cancer markers, and discovered a set of four cancer markers whose DMR signals, properly weighted, indicated the presence of cancerous cells in 48 out of the patients.
They then applied that same test to 20 additional patients, and confirmed cancer in all 20. This indicates an accuracy of better than 96 per cent—compared to the roughly 84 per cent accuracy of the current gold standard of cancer diagnosis, which uses chemical stains and visual inspection under a microscope…and the DMR test took only an hour.
No, a handheld device can’t replace a giant MRI. But at a cost of only a few thousand dollars, the new DMR device holds promise of reducing healthcare costs, speeding the early diagnosis of cancer, and points the way to quick diagnosis of many other diseases that usually require long waits and large quantities of tissue.
Isn’t it great living in the future?