Developments in hybrid imaging are increasing the utility of nuclear medicine while improving patient safety and cost efficiency significantly through reduced need for repeat examinations.

Nuclear medicine is seeing a shift toward digital technologies and a renewed focus on analytics. Nuclear and molecular imaging is becoming clearer, sharper, and cost-effective, and this change is being driven by both clinicians and patients. Nuclear-imaging methods, such 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 radiolabeled compounds into tomographic scanners that can accurately resolve the distribution and kinetics of an array of either gamma-ray or positron emitters. The examination methods that use PET-CT and SPECT-CT scanners are the most important molecular imaging techniques in nuclear medicine.

Indian Market Dynamics

The Indian nuclear medicine equipment market witnessed a major decline in 2014, with sales of only about 19 systems, valued at Rs.115 crore. The market for PET scanners was estimated at Rs.105 crore, with sales of 13 units. There is better realization for PET scanners, as buyers are upgrading their equipment from 16-slice to the better contrast and spatial resolution offered by 64- and 128-slice systems.

While GE, Philips, and Siemens are the three leading vendors marketing PET scanners with an equal market share, GE and Siemens are the major vendors in the SPECT scanners segment.

Global Scenario

The global nuclear medicine imaging market for PET and SPECT equipment is forecast to reach Rs.14000 crores in revenues by 2020. The demand for nuclear medicine services in the Asia-Pacific region is anticipated to grow with increasing incidences of cancer, cardiovascular and neurological diseases. South Asia and Southeast Asia are showing great potential in terms of cardiovascular and neurological applications.

The growth of nuclear medicine in future will come through radiotherapeutics.Therapeutic applications for treating oncology cases are yet to be developed completely. Certain restrictions in nuclear medicine services such as shortage of radioactive isotopes, dearth of technical experts in hospitals, and high cost of materials continue to dampen growth significantly, especially in the cost-sensitive economies of Asia-Pacific region. New technologies may affect demand for nuclear imaging, and how healthcare reforms are influencing the market.

Transitioning from SPECT to PET

The SPECT and SPECT-CT markets are larger than the PET, PET-CT, and PET-MRI markets as these scanners have been in use longer and are less expensive, and their use has become routine for a wide range of indications. SPECT techniques are expected to be replaced ultimately by PET procedures.

A key driver for future growth in the nuclear medicine market will come from PET, with the major switch in cardiology from SPECT to PET. A real interest in PET in cardiology will arise from applications in cardiovascular diseases (atherosclerosis and vulnerable plaque). PET in neurology has also proven to be of high interest. Oncology will remain the primary area of interest for PET imaging with the introduction of more than half a dozen new tracers on the market within the next five years.

With rising concerns about radiation dose levels, imaging system vendors have developed iterative reconstruction software to improve the image quality of lower-dose scans. All the major imaging system vendors now offer this technology on their PET and SPECT to help lower dose levels by 30-50 percent. Although PET tracers are higher energy, the much shorter half-life compared to SPECT translates into lower patient dose. The dose for perfusion imaging can be lowered further with the use of stress-only PET imaging protocols in the future. Over the last decade, PET image reconstruction technology has been designed to provide better image quality, reduced acquisition time, and lower injected dose. Current PET iterative reconstruction technologies, such as time of flight (TOF) and ordered-subsets expectation maximization (OSEM), force a compromise between image quality and quantitation.

Advancing Hybrid Imaging with PET-CT and PET-MRI

Hybrid imaging is being used to combine structural and molecular imaging - revealing molecular processes in vivo while depicting their anatomic location and the technique could mark the dawn of the era of personal medicine. Innovations in hybrid nuclear imaging promise to further increase the utility of hybrid nuclear imaging, while significantly improving patient safety and cost efficiency, through reduced need for repeat examinations. The advent of hybrid imaging has enabled PET-CT imaging to undergo explosive growth. PET-CT combines both the molecular and anatomical view to allow clinicians a broader perspective into the patient's condition. This technology has witnessed widespread adoption, along with SPECT-CT across the board.

Second Opinion
Hybrid Imaging - A Novel Modality

Hybrid imaging is the peanut butter cup of radiology, two complementary but very different imaging modalities rolled into one. Early uses of SPECT-CT have been in oncology, but other uses exist in cardiology and general nuclear medicine. In oncology, SPECT-CT scan improves the otherwise poor resolution associated with the use of monoclonal antibody ProstaScint (indium 111 capromab pendetide) in the assessment of prostate cancer. A second use is the assessment of neuroendocrine tumors, which tend to be very small and can cause problems in detection and delineation of the extent of the disease. Presurgical lymphoscintigraphy with SPECT-CT scan may minimize surgical intervention by defining the presence of cancer in sentinel lymph nodes.

In cardiac imaging, CT scan can eliminate attenuation artifacts that may obscure coronary disease from SPECT scan, while providing useful information about the coronary arteries. Anatomic detail can help in the diagnosis of infection when imaging with gallium. CT scan is also useful in detecting parathyroid adenomas and distinguishing them from other anomalies.

Oncology accounts for majority of PET-CT scans done because advances in detectors and software have dramatically cut scan times and stretched coverage, making whole-body examinations not only feasible but clinically recommended. Whole-body PET-CT scans lead to more accurate staging and restaging of cancer than can be achieved with the more routine scans that run from the base of the skull to the upper thigh.

Although nuclear-based derivatives of CT predominate, they are not the only hybrids. Lately, CT, MRI, and even PET scans have been combined with ultrasound to provide the anatomical and functional context for real-time sonography. These examinations are typically conducted to provide interventional guidance, leveraging diagnostic scans from CT and other imaging modalities. The data are downloaded into ultrasound scanners and the datasets co-registered, so anatomical or functional views change to match the real-time ultrasound.

Dr Parul Mohan
Senior Consultant & HOD, Nuclear Medicine,
Fortis Flt. Lt. Rajan Dhall Hospital,
Vasant Kunj

Hybrid PET-MRI scanners have become commercially available in the past years but are not yet widely distributed. The combination of a state-of-the-art PET with a state-of-the-art MRI scanner provides numerous potential advantages compared with the established PET-CT hybrid systems, namely, increased soft tissue contrast; functional information from MRI such as diffusion, perfusion, and blood oxygenation level-dependent techniques; true multi-planar data acquisition; and reduced radiation exposure. PET-CT scanners on the market offer digital PET detectors, allowing improved image clarity over traditional analog photomultipliers. The current PET-CT scanners employ digital silicon photomultiplier detectors instead of traditional analog detectors, reportedly doubling the sensitivity gain, volumetric resolution and quantitative accuracy over that of analog systems.

The current PET-MRI technology is hampered by several shortcomings compared with PET-CT, the most important issues being how to use MR data for PET attenuation correction and the low sensitivity of MRI for small-scale pulmonary pathologies compared with high-resolution CT. Moreover, the optimal choice for hybrid PET-MRI acquisition protocols needs to be defined providing the highest possible degree of sensitivity and specificity within the constraints of the available measurement time. A multitude of new acquisition strategies of PET and MRI not only offer to overcome current obstacles of hybrid PET-MRI but also provide deeper insights into the pathophysiology of oncological, inflammatory, or degenerative diseases from the combination of molecular and functional imaging techniques.

Applications and the future of hybrid imaging 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-MR in particular. Hybrid imaging with SPECT-CT, combining functional SPECT with CT, has evolved over the last decade with advances in both technology and clinical application. While overshadowed by the phenomenal success of PETCT, there has been increasing accessibility to multi-slice SPECT-CT aided by a wide range of clinically available radiotracers, lower cost and existing infrastructure within most nuclear medicine and/or radiology departments. SPECT-CT is likely to become increasingly organ-specific, with the use of cadmium zinc telluride (CZT) solid state detectors.

All three combinations of hybrid imaging - PET-CT, SPECT-CT, and PET-MRI - are at a technological state where they can be used clinically, but this mandates a multidisciplinary approach. Advances in data handling, image processing, and reconstruction will yield quantitative data, similar to those acquired in PET.

Integrated data-based technologies. Hybrid imaging in nuclear medicine is creating a patient-centric approach. Major technical advances continue to be made in all modalities, while the development of faster, more powerful computers has led to advanced image-analysis methods and processing algorithms that can be used to enhance images and extract novel, often quantitative, information. The establishment and mining of large image databases using informatics approaches is now being used to relate multidimensional data.

More and more clinicians are looking for ways to quantify images. Being able to compare the change in the size of a tumor before and after treatment allows clinicians to objectively determine the extent of the disease and effectiveness of treatment. As clinicians look to implement more preemptive and definitive treatment programs, they are demanding access to integrated, comprehensive data on the patient's diagnostic history. Access to more integrated diagnostic imaging technology will continue to be critical for improving patient outcomes. With access to more data, clinicians are looking for ways to customize treatment for patients, based on their anatomy and specific disease.

Data coupled with digitally advanced imaging tools can help clinicians make faster and more decisive disease detection, leading to more patient-specific therapy guided by molecular imaging. The expanding toolkit of molecular imaging techniques and agents could open new dimensions to personalized medicine in nuclear medicine. Radical improvements can ultimately be translated into high image quality, increased diagnostic confidence, improved treatment planning, and faster workflows. Diagnostic imaging continues to evolve and as the industry continues to ride the innovation wave, it will be critical to take a step back and make sure innovations meet the broader goals of increasing clinical performance, enhancing the patient experience, and providing economic value.

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