Combining PET or SPECT with CT allows the lesions to be identified easily by virtue of its high sensitivity and contrast which is leading to an increase in installations of hybrid systems and a corresponding decline in standalone PET and SPECT systems worldwide.
Nuclear medicine remains a vibrant and dynamic medical specialty. Nowadays, the usage of nuclear medicine procedures is expanding, especially as single photon emission computed tomography (SPECT) and positron emission tomography (PET) have advanced from simple camera systems that captured projections of 3D distributions of radiolabelled compounds into tomographic scanners that can accurately resolve the distribution and kinetics of an array of either gamma-ray or positron emitters.
The frequently critical need to precisely localize lesions within the anatomic context may not be possible with PET or SPECT alone. Combining them with CT allows the lesions to be identified easily by virtue of the high sensitivity and contrast of PET and SPECT. This is leading to an increase in installations of hybrid systems and a corresponding decline in standalone PET and SPECT systems worldwide. While SPECT/CT is expected to become the one-stop clinical solution for orthopedic and infection imaging, the combination of spiral CT and PET will remain relevant for conventional scintigraphy.
Over the years, the nuclear medicine equipment market has witnessed various new products being launched, coupled with various technological advancements. These advancements have led to the improved use of many existing nuclear medicine equipment as well as the introduction of some new ones.
During the last decade, PET/CT and SPECT/CT have made advances in research and clinical application of fusion imaging. These two modalities are established in the market today, with PET/CT being the standard-of-care in oncology and SPECT/CT an upcoming hybrid modality currently being used mainly for cardiac scans.
Hybrid imaging platforms represent a significant advancement for clinicians by presenting them with both anatomical and physiological images of patient's organs, tissues, and tumors in a single scan. Nonetheless, to realize the full potential of hybrid imaging modalities, researchers and clinicians across the globe are combining their expertise to develop novel platforms.
Novel collimator designs. New collimator designs, including multi-pinhole and locally focusing collimators arranged in geometries that are optimized for cardiac imaging have been implemented to reduce imaging time and radiation dose. These new collimators have been coupled with solid-state photon detectors.
Advanced scanners. The new SPECT scanners demonstrate up to a seven-fold increase in photon sensitivity and up to two times improvement in image resolution. Although PET scanners are used primarily for oncological imaging, cardiac imaging can benefit from the improved PET sensitivity of 3D systems without inter-plane septa and implementation of the time-of-flight reconstruction. Additionally, all major PET vendors now implement resolution recovery techniques. These new methods improve image contrast, image resolution, and reduce image noise for cardiac imaging.
Hybrid imaging with CT and PET or SPECT increases the diagnostic sensitivity and specificity of the single modality, thus making the integrated approach more accurate. The same can be expected from adding MRI to PET or SPECT.
Beyond PET/CT and SPECT/CT. Over the past 4 years, PET/MRI has been making inroads as well as could eventually supplant PET/CT as the modality of choice in some areas of oncology, neurology, and cardiology. The excellent soft-tissue contrast of MRI and the multifunctional imaging options it offers, including spectroscopy, functional MRI, and arterial spin labeling, complement the molecular information of PET. Simultaneous PET/MRI also allows doctors to follow tracer distributions over time and combine quantitative molecular PET information with information on cellular densities, flow, and perfusion, including data obtained from advanced MR-based spectroscopy, diffusion, and perfusion studies. The development of a fully integrated PET/MRI system is technologically challenging. It requires not only significant modifications of the PET detector to make it compact and insensitive to magnetic fields but also a major redesign of the MRI hardware.
Indeed, PET/MRI has the potential to broaden horizons in the emerging field of molecular imaging, because complementary anatomic and biologic information is obtained and synergisms of both modalities can be expected. The novel imaging technology may not enter clinical routine before its impact on diagnostic accuracy has been proven and the effect on therapy management and cost-efficiency has been considered and validated.
Challenges and Opportunities
Incessant introduction of new and advanced products, investment in modernization of diagnostic imaging centers, development of new radiotracers, increasing use of SPECT and PET scan results, alpha radio immunotherapy-based targeted cancer treatment, rising incidence and prevalence of cancer and cardiovascular diseases, strong product pipeline, and growing demand for nuclear medicine procedures in the emerging market are lucrative opportunities for nuclear medicine equipment.
The exorbitant cost of hybrid scanners puts them out of the reach of small medical imaging clinics and rural setups, making them affordable only to multispecialty hospitals and larger clinical setups. With companies building most systems through in-house research and looking for a quicker return on investment, increased government funding for product development could reduce the cost of advanced hybrid imaging platforms.
Developing alternative fusion platforms - optical imaging with PET - will also help hybrid imaging solution providers decrease the overall cost of systems. In addition, factors including stringent regulatory guidelines, shorter half-life of radiopharmaceuticals, competition from conventional diagnostic procedures, growing adoption of refurbished diagnostic imaging equipment, and hospital budget cuts act as a challenge for the market.
Molecular imaging is one of the best single imaging modalities at this time, with combined multimodality imaging soon to become the top choice, particularly when radiotracers only currently used for research become available for widespread clinical use. The future to some extent is dependent on reimbursement, which in some countries remains limited, while other member states enjoy a more liberal and evidence-based reimbursement policy.
SPECT/CT is likely to become increasingly organ-specific with the use of cadmium zinc telluride (CZT) solid-state detectors. Advances in data handling, image processing, and reconstruction will yield quantitative data, similar to those acquired in PET. Both PET and SPECT are ultimately limited by considerations of the radiation dose absorbed within tissues and the specificity of the radiotracer. There are certainly improvements possible in system design, image acquisition, and reconstruction.
Applications will be defined by the availability of molecular tracers. New tracers that become very specific, thus providing very little anatomical background information but very high sensitivity and specificity, will promote the use of hybrid imaging, and PET/MRI in particular. PET/MRI may emerge as a new powerful multimodality technique in clinical oncology, offering considerable potential for imaging applications beyond correlation of functional and anatomic images.
The upcoming developments could include the simultaneous acquisition of multifunctional data including PET tracer uptake, MR spectroscopy, or fMRI along with high-resolution anatomic MRI. In future, the impact of chemistry on nuclear imaging is likely to be greater than that of physics or engineering.