The PET Unit at the BIC:
A Long History of Staying Ahead
Positron Emission Tomography (PET) allows neuroscientists to investigate, brain function and disease in living individuals. Amongst others, PET provides quantitative estimates of rates of oxygen and glucose consumption, concentrations of neuroreceptors, activity of enzymes as well as deposition of abnormal proteins in the brain. In fact, PET has been present at the Neuro since the mid 1970’s, making it indeed one of the oldest PET units in the world. After humble beginnings with one scanner acquired from the Brookhaven National Laboratory in Upton, New York, a series of scanners were locally assembled or purchased to keep our research capacity in humans at the forefront of the field. In the early 2000’s, a small animal scanner was procured, opening up for us the field in pre-clinical imaging. In parallel, a Radiochemistry Laboratory with its own cyclotron (we have had 2 so far) has been one of the most productive of such installations worldwide and has made available a large variety of ever renewed and expanding radiopharmaceuticals, a process absolutely critical to maintaining a vibrant PET research program in Neurology and Neuroscience. Striving to always offer state-of-the-art infrastructures, and associating with the world-class researchers in multiple neuroscience fields, the PET Unit of the Neuro is universally recognized as one of the premier such centers in operation today.
PET is an advanced imaging modality which has absolutely unequalled capabilities for safely studying normal and abnormal physiology in the living. An essentially noninvasive technique, it rests on the intravenous injection, at doses that are vanishingly small, of one of a series of molecules (radiopharmaceuticals) with biological properties, which will guide them to a specific molecular process in the body. Those radiopharmaceuticals are tagged with a very low amount of atoms emitting a type of radiation detectable from outside of the individual being studied by specialized scanners that will determine the area of emission of the signal within that subject. We can therefore follow those agents over time and space, allowing us to quantify with high precision the activity, concentration and biochemical properties of literally hundreds of different types of molecules in the body, in health and disease. This helps researchers understand how the brain (we are at the Neuro! Other organs can of course be similarly evaluated) can accomplish its incredibly complex operations when things go well, or what might explain a number of diseases in order to elaborate new or more effective therapies.
As a center dedicated entirely to research, we conduct experiments, always under the very strict supervision of institutional committees and governmental agencies whose role is to ensure safe conditions for research volunteers, in human subjects. We also pursue research in animals, often bearers of conditions mimicking diseases found in humans, to gain insights on the mechanisms driving those problems and also to develop and validate new approaches which might later be used in humans, or, again, to better understand normal biological functions. Again, this is done following strict ethical rules on how to handle and treat the animals involved.
PET studies: Two crucial arms
PET imaging involves essentially two types of activities: preparation of the radiopharmaceutical, and imaging of its distribution in the body.
Positron emitting atoms used to label the molecules designed to bind to specific targets in the body are generally (although by no means exclusively) relatively light atoms, with a nucleus that shows a ratio of neutrons to protons too low for those particles to “live peacefully” together. In order to rebalance that ratio, the nucleus of the atom can undergo different types of modifications, but for some atomic species, the preferred alternative is to transform a proton into a neutron. This involves for the proton to get rid of some energy and of its positive charge, and it does so in large parts by emitting a small particle called a positron (hence, positron emission tomography), which is at the origin of the signal that will be detected by the scanner used for imaging.
As just mentioned, positron emitting atoms have unstable nuclei. In fact, those we can use for PET imaging are unstable enough that they transform into a new species (one less proton, one more neutron) quite rapidly, losing half of the original form of the nucleus over periods of minutes to less than two hours (that period of time is called, quite pragmatically, the half-life of the radioactive sample). In addition, there is no natural mechanism that keeps forming them, so they literally need to be produced on demand each time you want to run a PET imaging session. This involves taking stable, naturally occurring atoms, and turning them into the kind where there will be too many protons per neutron as described above, by injecting a proton into them. The way to do this is to take protons, accelerate them to tremendous speeds, and then slam them into the nucleus of the natural, stable atoms (there are other approaches for a small number of positron emitters we do not really use much). An efficient way to do that is to use a cyclotron, a device very good at pushing charged particles, including protons, to the type of speed needed, while remaining small enough to be housed in a laboratory of reasonable size. The PET Unit of the Neuro operates an accelerator of that sort, which allows us to produce a number of species of positron emitting atoms.
We now have positron-emitting atoms generated by our cyclotron. By themselves though, those are not very useful because in general they do not have very interesting biological properties. They really become usable after they have been attached to a molecule that will take them to the molecular target we wish to study inside a human subject or an animal. This involves having at our disposal a molecule with the desired biochemical properties and to which the radioactive atom can be bound. The type of radiochemistry operations needed to accomplish this have reached a high level of sophistication, allowing specialized radiochemists to attach positron emitting atoms to a large number of molecules without altering their function (so that they will still react properly with their molecular target). Developing ways to create new radiopharmaceuticals with completely different, or even simply better, properties, can sometimes involve original, new and complex procedures. In addition, once a technique has been established, the actual synthesis of radiopharmaceuticals requires working in an environment quite unlike that of a standard chemistry laboratory. One needs to start with relatively large quantities of radioactive material which keeps decaying as you proceed through the different steps leading to the final product, and therefore to work beyond shielding protecting the operator from radiations, using reactions that need to proceed quickly and running quality control of the final product as rapidly, but still thoroughly, as possible. A high degree of training, infrastructure and equipment capable of operating at high radiation levels while ensuring the safety of personnel, are all necessary to accomplish such tasks, and represent significant investments in manpower, hardware and buildings.
At this time, the PET Unit operates a HRRT (High Resolution Research Tomograph, Siemens), ahead only PET scanner with one of the best available spatial resolution currently available (approx 2.4 mm; modern commercial units boast resolutions on the order of 4 mm). A second head dedicated scanner, developed at Sherbrooke University by the team of Dr Roger Lecomte, will arrive in late Summer, 2020, and will offer a revolutionary improvement in resolution at approximately 1.3 mm, allowing exploration of small brain structures so far much beyond the imaging capacities of other scanners.
We also offer small animal, preclinical PET scanning on our microPET system, which can image rodents (mice, rats) and very small non-human primates (marmosets).
How to do a PET study
Access is open to any investigator wishing to conduct human or animal PET research, provided proper approvals from appropriate REBs and Health Canada (human studies only) are obtained.
Pricing for PET studies will vary significantly depending on the tracer required exact acquisition protocol and a variety of other parameters. We strive to keep prices to as low a level as compatible with the operation needs of the PET Unit. Information for a specific project can be obtained by contacting either Dr Gassan Massarweh, Director, Cyclotron and Radiochemistry Laboratory (gassan.massarweh [at] mcgill.ca) or Dr Jean-Paul Soucy, Director, PET Unit (jean-paul.soucy [at] mcgill.ca). The PET Unit operates at full capacity most of the time. Contacting Dr Massarweh or Dr Soucy is usually necessary to ensure timely access to the facility.
Our PET staff is supported in part by a generous donation from the Louise and Alan Edwards Foundation.
|Dr Jean-Paul Soucy||Medical Director|
|Christian Janicki||Radiation Safety Officer|
|Stephan Blinder||Academic Associate|
|Reda Bouhachi||Systems Manager|
|Karen Ross||Micro PET Unit, Research Assistant|
|Hung-Hsin Hsiao||Research Technician|
|Arturo Aliaga||Research Technician|
Radiation Safety Manual for Nuclear Substances, Radiation Devices And Cyclotron (Class II) Facilities - Download PDF
Public Information Disclosure Program:
The CNSC requires that the owner of a cyclotron (class II nuclear facility) has a program to assess public knowledge and ensure that key groups and the public are informed about the cyclotron in order to comply with the CNSC public information and disclosure program (PIDP).
The Public Information Program (PIP) keeps the target audience informed about the operation of the Montreal Neurological Institute and Hospital’s Cyclotron facility and answers any questions related to the health and safety of the workers, the public and the environment in an open and transparent manner.
As part of that program, the Cyclotron facility will disclose on this website information about any following events within 24 hours of the event as it occurs:
- Lost, theft or unauthorized release of nuclear substances;
- Work accident or injuries;
- Any criminal act or sabotage;
- The incident resulting in exceeding any regulatory limits (e.g. contamination limits, dose limits);
- unplanned or significant interruptions of facility operations (i.e. failure of safety equipment, major breakdown);
- damages caused by fire;
- impact of natural events (i.e. earthquakes, floods, lightning);
- transport vehicle incidents or accidents;
- any other incident that may have an impact or is perceived to have an impact on the safety of workers or public.
Proactive Disclosure - May 9, 2018
The ventilation system at our facility is equipped with a 24/7 monitoring system. The alarm is triggered when there is any problem with the ventilation system like a drop in the pressure etc. which also includes exhausted air.
A continuous alarm was triggered on Tuesday, May 8 at 18:00 after regular working hours. This happened 8 hours after the last cyclotron operation and no one was working in the lab at that time. Since only short-lived radioisotopes are used (C-11, F-18), all radioactive tracers inside hot cells had decayed to very low and safe levels within a few hours after the last cyclotron operation and there has been no radiological consequence to this ventilation problem.
The McGill heating, ventilation and air conditioning (HVAC) team started investigating the problem as soon as they were notified on Wednesday 9. Using an inspection camera, the McGill HVAC team has identified that the problem was due to the presence of water inside the duct running underground in the parking lot adjacent to the cyclotron vault. Water was pumped out of the duct on Friday, May 18 in the morning and the ventilation was immediately back to normal.
McGill HVAC team will continue monitoring the situation and will do regular inspections and maintenance to make sure the ventilation system remains fully operational at all times.