By Katerina Maida, MD Nuclear Physician, Director of Nuclear Medicine Department - PET / CT, Athens Medical Center
In the last 20 years we have entered the era of hybrid imaging using the SPECT / CT, PET / CT and PET / MRI systems, which combine the functional and molecular imaging of Nuclear Medicine with the morphological imaging of CT with the morphological and in many cases and functional imaging of MRI.
Single Photon Emission Computed Tomography (SPECT) already has a long history of tracking and monitoring coronary heart disease. It is a more sensitive method than the simple two-dimensional scintigraphy, it gives out three-dimensional images to better locate and highlight focal points that are smaller or are potentially covered by the depicted adjacent physiological structures. It is combined with morphological CT and MRI tests performed at different times and on different machines with the appropriate software, thus increasing diagnostic accuracy.
Applications of SPECT
In the heart:
- Detection and monitoring of known coronary artery disease
- Detection of myocardial viability after infarction
- Assessment of heart function, wall mobility, ejection fraction and other functional parameters
In the brain:
- Estimation of cerebral blood supply in known cerebral vascular lesions
- Early detection of Alzheimer's disease and discernment from dementias caused by other reasons
- Study of Parkinson's disease and its discernment from essential tremor (DaTSCAN)
In bones:
- Detection of osteoblastic and mixed bone metastases
- Estimation of the final decline in lytic bone metastases after treatment
- Detection of primary tumors such as the osteoid osteoma
- Investigation of causes of back pain such as recent spondylolysis
In the lungs:
- Detection of pulmonary embolism, especially in young and pregnant women (where the radiation dose of the breast is much smaller than in computed pulmonary arteriography) and monitoring of chronic thromboembolic disease
In tumors:
- Detection of neuroendocrine tumors (carcinoid, parathyroid adenomas, pheochromocytoma)
- Detection and monitoring of neuroblastoma in children
Positron Emission Tomography (PET) has proven its value through a variety of research studies and is now a necessary step for initial screening and monitoring of patients with neoplasms:
- It provides important information about the biological behavior of cancer and, by extension, the prognosis
- Extensively assesses the extent of the disease, thus in many cases changing the stage of the disease as well as the treatment plan
It is an integral part of the algorithm for early assessment of response to therapy, assessment of therapeutic outcome after chemotherapy end, and / or radiotherapy and control of relapse in the majority of tumors, with primary examples of lung, colon bowel, cervical and head cancer, as well as lymphomas.
The basis of PET is metabolic and is related to the fact that cancer cells and surrounding stromal cells have increased energy and structural needs because of their proliferation in relation to normal tissues or they predominantly express membrane receptors.
Taking advantage of this property, we use labeled glucose (F18-FDG), labeled structural stones, such as e.g. choline, methionine and labeled antibodies against specific receptors, such as e.g. versus somatostatin receptors (DOTA derivatives), to highlight the cancerous tissue. Molecular imaging enables us to detect changes in cell and tissue levels that occur prematurely in the course of the disease, in many cases before even structural, anatomical alterations in CT and MRI have manifested themselves.
The combination of PET and CT in one test has the advantage of better and correct localization of metabolically active lesions, while their morphological characteristics are evaluated with the ability to perform full diagnostic protocols for each method. Today, PET / CT is widely used in the vast majority of cancers, and in some cases the PET / MRI method appears to be superior, as for example in the evaluation of brain tumors and prostate cancer with radiopharmaceuticals specific to each case (C11 -methionine and Ga-68-PSMA).
The main applications of PET / CT with the most commonly used F18-FDG radiopharmaceutical are summarized in the following:
Diagnosis of primary focal point
Characterization of single pulmonary nodule, pancreatic mass, and detection of primary focal point of cancer of unknown origin, such as metastatic cervical lymphadenopathy, hepatic or bone metastases.
Estimation of the stage of the following diseases:
- Hodgkin's and non-Hodgkin's lymphomas
- Lung, head – neck cancer, including biopsy guidance
- Locally advanced breast cancer
- Cancer of the esophagus, pancreas and colon
- Malignant melanoma
Interim response to treatment and detection of residual disease after completion of treatment for:
- Hodgkin's lymphoma and non-Hodgkin's lymphoma
- Head – neck and lung cancer
Detection of relapses for:
- Colon cancer
- Lung cancer
- Head neck cancer
- Breast cancer
- Ovary cancer
- Myeloid and differentiated thyroid cancer
- Malignant melanoma and high grade malignant glioma (III or IV)
