By Farhad Daghighian
It’s well known that positron emission tomography (PET) imaging provides physiologic, molecular and functional information on tumors and various organs.
One way to improve biopsy results is to leverage the physiologic (metabolic or immunologic) information provided by PET imaging to effectively target and sample tissues, especially when X-ray CT or ultrasound does not identify the abnormality.
Cost and logistic issues hinder the wide use of PET in interventional settings. In order to make interventional PET economically viable, it should be portable between the radiology and interventional rooms. While in a radiology department it will be placed parallel to a CT scanner for routine PET/CT scanning. When needed, it will be moved to surgery rooms, ER, ICU, and radiotherapy suites.
Prescient Imaging LLC has developed a low-cost, portable PET scanner (P-Arm) that can make PET imaging accessible for interventional procedures. P-Arm has wheels and is a portable PET scanner, similar to that of X-ray C-arm. One set of its detectors moves under the patient, while another set is placed above the patient for complete 360 degree views while the patient is within the scanner.
18F-FDG PET can identify the most metabolically active portion of a tumor or abnormality, and distinguish between biologically aggressive and non-aggressive regions of malignant masses, thus providing a greater chance to effectively sample suspicious tissues and obtain a higher quality biopsy sample (higher tumor content) suitable for molecular diagnosis. Other radiotracers, with different biological properties (such as monoclonal antibodies), have shown promise for advancing precision medicine by detecting occult lesions and enabling their targeting with biopsy.
Physicians at Rambam Health Center in Israel retrospectively assessed data from 311 consecutive patients with lung nodules who underwent 18F-FDG PET/CT and CT-guided FNA within an interval of less than 30 days. They concluded that anatomy- and metabolism-based fine-needle-aspiration guidance using information provided by both 18F-FDG PET and CT may improve the accuracy of histologic examinations, decrease the rate of false negative results, and thus increase the probability of achieving a definitive diagnosis.
PET is being increasingly used to aid interventional procedures at major academic centers. For example, Dr. Stephen B. Solomon used a PET/CT scanner that was installed in the Center for Image-Guided Intervention at Memorial Sloan Kettering Cancer Center to image liver tumors in more than 300 patients, before and after radioablation, in order to detect any untreated region of the tumor and complete the therapy. Also, in a recent pilot study they have demonstrated the feasibility of performing delayed PET image-guided biopsy using 89Zr anti-PSMA or trastuzumab radiotracers without tracer reinjection. This is an efficient method to optimize workflow, since 89Zr half-life is 79 hours.
This portable PET scanner is novel in its form and function, and will unleash the power of PET imaging in therapy settings (surgery, radiation, and ablation therapy). It will transform PET from a diagnostic system to a theranostic one (theranostics, meaning therapeutic and diagnostic at once) that can be used at the point-of-care. It will bring urgently needed physiologic imaging to other interventions such as percutaneous thermal ablation and Y-90 embolization.
Catheter-based intra-myocardial delivery of therapeutics such as stem cells, anti-inflammatory agents, and genetic material is being explored for the treatment of heart disease. Current technologies rely on electrical or anatomical features to guide delivery to specific locations in the heart (e.g. fluoroscopy, electromechanical mapping). Molecular signals from PET radiotracers provide functional information that may be useful in guiding intra-myocardial therapeutic delivery. A PET scanner in an intervention room may identify injured myocardium via endocardial detection of IV-delivered PET radiotracers in real-time PET images, as well as intra-ventricular radiation detectors, and guide delivery of therapeutics to injured tissue via direct intra-myocardial injections.
With portable imaging in the operating room or a catheterization laboratory come many new theranostic procedures never imagined before. Clinical demand is moving rapidly, and requires a reconfiguration of technology in which nuclear tracers are used to guide treatment in real time. By reconfiguring PET-design we are afforded new windows into the future of patient theranostics never achieved before in medicine.
About the author: Farhad Daghighian, PhD is president and chief scientist at Prescient Imaging, LLC