The examining of a disease was a hard process before the development of the imaging method. Medical professionals trusted the senses in their fingertips to examine if someone had a broken arm or leg. In time, scientists in different disciplines invented and improved technology to examine diseases by processing and verifying more precise data. Medical imaging is now one of the most improved techniques used for diagnosis of diseases, a technique used to create images of diseased parts of the body. After the discovery of the X-ray by German physicist Wilhelm Conrad Rontgen, the method of image creation started to take part in medical diagnosis methods in the first decade of the twentieth century. Recently, many different imaging techniques have been implemented for discrete diseases.
Nuclear medicine is a specialty area in medicine in which the energetic particles emitted from radioactive materials are used to diagnose and treat diseases. Short-lived isotopes are embedded into the human body and biologically active tissues absorb the embedded isotopes. This method is used to identify tumors and fracture points in bones. By using a technological device, the elementary particle photon is detected by sensitive detectors and then the data is converted into image. Gamma cameras capture the isotopes in the body to give a 2D image. The emitting of gamma rays is captured by sensitive detectors. This is generally how an imaging method works in nuclear medicine. What follows now is an overview of several imaging techniques and their advantages.
Magnetic Resonance Imaging (MRI)
MRI is one of the most common imaging techniques used to visualize the internal structure of the body by providing high quality images. This technique is based on the principles of the Nuclear Magnetic Resonance (NMR), which is a physical phenomenon in which absorption and emission of electromagnetic radiation by a nuclei in the magnetic field can be visualized. So, MRI provides an opportunity to observe the magnetic properties of the atomic nuclei of the human body. It has more advantages over other imaging techniques (such as Computed Tomography CT and X-rays) while observing the soft tissues of the body as brain, muscles and heart.
As many people may know, MRI consists of a large magnet which aligns the magnetization of the atomic nuclei and a radio frequency field which alters the direction of the magnetization routinely. Then, the 2D image of the body or a certain part of the body is recorded by a scanner.
Positron Emission Technique (PET)
One of the most accurate methods for diagnosing, staging and re-staging various kinds of methods is Positron Emission Tomography (PET). PET works as follows: a specified amount of radioactive substance is injected to the designated subject or a region of the body. When radioactive atoms decay, they release positrons. Positrons, antiparticles of electrons (+e), immediately collide with electrons (-e) and the annihilation process (+e + -e = photons) is formed and Gamma rays is produced. The emitted Gamma rays are detected by sensitive detectors and the image is constructed. PET is useful in receiving data about each organ of a body and their functions, and it is this data that is used to diagnose the disease. PET is very useful for studying the brain and its functioning and also provides a unique image of where the cancer cells are located in the body. Briefly, sugar molecules attached with radioactive isotopes are injected to the human body. Once doctors are sure that the sugar molecules are distributed to all parts of the body completely, the image is taken. Unhealthy cells eat up sugar molecules a lot faster than healthy cells. Then, only radioactive particles are left behind in the cancer cells which are exposed to the process explained above (+e + -e = photons). The formed gamma rays are detected and an image is formed.
However, it is really hard to localize the cancer cells when these cells are hand in glove with the soft tissues or hiding behind the skeleton. In that case, scientists compare the images by both PET and MRI to locate the cancer cells as precisely as possible. To treat a cancer cell precisely, this problem needs to be overcome first. Recently, particle physicists at the University of Oslo working at CERN [www.mergeous.com/articlecon.asp?aid=45] (the world’s largest particle accelerator) added a new dimension to this problem by inventing a new design of imaging technology. They combined PET and MRI in the same machine. They constructed a small PET machine which was able to be placed in an MRI machine. By doing this, they aimed to take two images at the same time, lowering the radiation exposure on people, and to decrease the statistical errors possibly made by the medical personnel when comparing the two images. Fortunately, they achieved their goals and invented a high sensitive and a low radiation machine. They improved upon new types of detector technologies by using photomultiplier tubes and light guide fibers. With these new detectors they were able to detect gammas more precisely and also to lower the image taking time. Erlend Bolle, a researcher in the field of high energy physics at the University of Oslo, said that [www.sciencedaily.com/releases/2012/08] they got this new detector idea from CERN which consists of several high tech-detectors.
Another practical application [www.mergeous.com/articlecon.asp?aid=45] of the particle accelerators is as follows: recently, a collaboration of researchers from Northern Illinois University (NIU) and particle physicists at Fermilab and Argonne National Laboratory have been trying to improve new detector technologies to have better 3D images of the human body to help cancer patients. Their aim [www.symmetrymagazine.org/article/april-2012] with this new particle detector was to attain better results by using protons for computed tomography (CT) instead of X-rays. A couple of years ago, the same group of researchers from NIU collaborated with a group of scientists from the University of California, Santa Cruz and Loma Linda University Medical Center to build a prototype proton system. They proved the advantages over the proton computed tomography to the X-rays CT. X-rays and protons show different characteristic properties when they get into the matter: X-rays start to give up their energy once they get into the matter. They affect healthy body parts like organs, tissues, cells, as well as tumors as they travel into the body. However, a proton behaves very differently to X-rays and it releases most of its energy at the end of its path. Because they do not deposit their energy along their path, they do not affect healthy tissues. By adjusting the speed of a group of protons, scientists can determine how long it goes on its path and where it deposits most of its energy to kill the tumor. This type of treatment can be a better option for soft tissues of the body such as the brain and pediatric tumors.
Sir William Henry Bragg, a British physicist and chemist, discovered the Bragg peak in 1903 which shows the energy loss of ionizing radiation during the particle’s travel into the matter. In Fig. 1 below, the vertical axis shows the dose produced by the proton beam when passing through the matter and the horizontal axis shows how far the proton beam goes before losing all of its energy. The figure illustrates two different kinds of protons produced by a particle accelerator of 250 MeV. As can be seen clearly in the figure, for protons, the Bragg peak occurs immediately before the protons come to rest. This means that they deposit most of their energy to their surroundings immediately before they come to rest. Therefore, this curve perfectly confirms that proton beams minimize the effect on surrounding healthy tissues. The purple line represents the photon beam, and it is clear that it deposits its energy gradually along its path.
Fig. 1: Brag Curve (reproduced from en.m.wikipedia.org/wiki/Bragg_peak)
There are many scientists from various disciplines working together to take science and technology one step further. As can be seen clearly in the work of cancer therapy with proton accelerators, if scientists from different unrelated disciplines come together and strive to advance technology to solve today’s problems, they could most probably overcome those problems and bring forward a new and problem-free world.
Kara is a freelance pop-sci writer pursuing a PhD in Physics.