Positron Emission Tomography HHHOLDORF What is Positron Emission

Positron Emission Tomography HHHOLDORF

What is Positron Emission Tomography (PET Scan) �PET Scan – uses radiation for making colored, three dimensional images. �Provides pictures of the body’s functional processes. �The machine identifies gamma rays that are discharged by a tracer (positron-emitting radionuclide) are injected into the body. �Computer analysis is used to reconstruct the images.

What is a Positron and how does it function in a PET Scan? � A Positron - Is antimatter and is similar to an electron. But instead of having a negative charge like an electron, the positron has a positive charge. The positron is not as common in the universe as the electron. Like electrons, positrons are also used in particle accelerator experiments. � Function in PET Scan - When radioisotopes are injected into the body, they break down and release the positrons. After traveling a few millimeters, the positrons collide with electrons. The collision produces gamma rays that are picked up by a scanner.

How a PET Scan Works �A radioactive substance is made in a cyclotron. �The radioactive substance is attached to a chemical such as glucose, ammonia or water. �The radioactive chemical becomes a radiotracer that is injected into a patient. �Once injected, the radiotracer will travel to places in the body that utilize the natural chemical. �The radiotracer breaks down in the patients body to produce Positrons (positively charged particles). �The PET scan indentifies the radiation emitted by the positrons

Why are PET Scans Important �Physicians use PET scans along with MRI scans and X-rays for diagnosing diseases. �Also, they are helpful in discovering if a current treatment is successful.

Procedures � Patients may drink water, but cannot eat for at least four to six hours prior to the scan. Patients may also be told not to consume caffeine for at least twenty four hours before the scan. � A small amount of the radiotracer is either injected into or is inhaled as a gas by the patient. � The radiotracer will reach the specific area in the body within thirty to ninety minutes. The patient must stay still and refrain from talking. � Once the patient is ready for the examination, he/she will lie down on the table. Then, the table will slide into a large opening in the machine. Afterward, the images of the patient are taken. � The process is not painful and the majority of the patients may leave after having the scan. Patients are instructed to drink plenty of liquids to flush the radioactive materials out of their bodies. Radiotracers usually leave the body within three to four hours after being injected.

Radionuclide's used N-ammonia � 15 O-water � 11 C-acetate � 11 C-methionine � 18 F-FDG � 13 F-FDG is the most common radiopharmaceutical used in PET worldwide. � 18

Pet Scans are Used to Diagnose Conditions �Epilepsy – scans can show the area of the patient’s brain that is affected. �Cancer – provides doctors information on the stage of the cancer, if the cancer has metastasized, and also helps doctors to choose the best treatment for the patient. �Alzheimer’s disease – measures the brain’s uptake of sugar and helps to provide a more accurate diagnosis. �Heart Disease – Aids in detecting which areas of the heart are damaged.

History �The PET scan was invented in 1973 by Michael E. Phelps, a UCLA medical examiner. Phelps was one of the first to show different parts of the brain are activated when performing mental tasks. He has also helped to advance medical imaging by producing four generations of PET scanners ( include the prototypes that all modern- day PET scans are based on)

History 1950’s �In 1953 a young daughter of Rhode Island farmer traveled to Boston to find a doctor to diagnose a neurological problem that left her unable to read. The neurosurgeon could not help her so he enlisted the help of Dr. Gordon L. Brownwell. �A year later, Dr. Brownwell invented a scanning machine that displayed the location of a tumor in the girl’s brain. The tumor was isolated and successfully removed. The technology that Dr. Brownwell invented was the basis of, and later evolved into PET scans.

Dr. Brownwell

History of PET -1970’s � In the 1970’s PET scanning was formally introduced into the medical community and at this time it was this new research modality that opened the doors where medical researchers could watch, study and the biology of human disease. �The first PET scanners held only a small amount of radiation to transmit an image ( therefore the images that were obtained by the scanners were of low quality and definition. Along with using the PET scans , a team of professionals were required ( chemists, physicists and physicians)

1980’s �During this time the technology underlying PET scans advanced greatly More precise images and resolution were developed on commercial scanners Many of the steps involved in operating a PET machine were automated and could be performed by a physician or trained technician. � This decreased the complexity of the scanning procedures and reduced the cost.

2000’s �Modern PET scanners are much more advanced, expensive pieces of equipment. �They are much easier to install and operate �They have evolved enough to even produce movies of parts of the body �Over the last several years the major advance in this technology is that it is combined with a CT scanner as one device. This modern PET/CT scanner decreases study times and provides much more diagnostic information.

Benefits �For many diseases, nuclear medicine scans yield the most useful information needed to make a diagnosis or to determine appropriate treatment, if any. �Nuclear medicine is less expensive and may yield more precise information than exploratory surgery. �By identifying changes in the body at the cellular level, PET imaging may detect the early onset of disease before it is evident on other imaging tests such as CT or MRI.

Risks �Pregnant and nursing women – must not have a PET scan. �Patients who have had a scan must avoid pregnant women, children, and infants for several hours after the scan. �Allergic reactions to the radiopharmaceuticals may occur but are extremely rare and are usually mild.

Case Study �The study presents a 55 year old post-menopausal woman who came for a routine screening mammogram. Bilateral mammography showed scattered fibro-glandular densities. A new 5 mm irregular density was seen in the right breast at the 1 o’clock position, 7 cm posterior to the nipple and evaluated as BIRADS-5, which is highly suspicious of malignancy. The ultrasound failed to identify the lesion A biopsy under stereotactic guidance was recommended.

Continued…. �The pathology from the stereotactic biopsy was benign glandular tissue �The patient also suffered a hematoma in addition �A delayed right breast needle – localized excisional biopsy of the tissue marker was performed after resolution of the hematoma and development of two new areas of fat necrosis. Pathology yielded discordant benign results once again but the patient remained BIRADS-5. MRI could not be performed due to the patients weight.

Continued…. �Breast PET or PEM (positron emission mammography) imaging revealed a post surgical area of 81 F-FDG uptake that is associated with granulation at the site of the biopsy with a moderate uptake of FDG (Fluorodeoxyglucose). Additionally, a 9 mm oval lesion of FDG uptake was identified as malignant. Two other areas of slight FDG uptake were found in the areas of fat necrosis seen in a mammogram. Afterward, a PET-guided breast biopsy was performed on the Patient. (PEM is a high resolution breast PET scanner).

Continued…. �Naviscan’s Stereo Navigator software was used to perform a high-resolution breast Pet-guided biopsy that made the lesion easier to see for vacuumassisted biopsy. The four scan biopsy usually takes twenty minutes. The lesion is targeted by the Stereo Navigator in three dimensions. To ensure that enough sample were taken, two biopsies were made. The biopsies imaged on the PEM scanner revealed levels of high FDG uptake.

Comparison �These photos compare the screening mammogram and the diagnostic PEM.

Results �Histopathology of the biopsy revealed Grade three infiltrating ductal carcinoma. Surgery was immediately performed on the patient. High-grade intraductal carcinoma was found after the surgery.

Conclusion �The case study proves that the breast PET or PEM scan is successful not only for locating lesions, but also for identifying lesion pathology by showing the uptake of FDG.