Mayur Patel, MD

Positron emission tomography (PET) has been available for clinical use since the early 1990s. Widespread use began in the late 1990s, after Medicare approved reimbursement for evaluation of solitary pulmonary nodule and non-small cell lung cancer. Subsequent approval of multiple, additional indications has increased the clinical applications of PET to the extent that it is now considered a "must have" modality for imaging centers and hospitals of all sizes. Although it took almost a decade, the transition from an academic tool to clinical practice has now been completed.

American Radiology Services (ARS), a Baltimore-based practice, initiated its PET program by installing a dedicated stationary PET scanner in one of its outpatient imaging centers in April 2000. In the summer of 2002, ARS added three more dedicated, newest generation scanners in strategic locations throughout its outpatient practice to meet the needs of an expanding marketplace.

Although there is a steady proliferation of various types of PET imaging services in the region, overall utilization to support these newer installations has steadily increased with approval of new indications. There are further expectations for increasing procedural volumes based on the approval of further new indications, with the most recent approval being the use of FDG-PET in breast cancer patients. Recent reports of recommendations by the Centers for Medicare & Medicaid Services (CMS), for significantly lowering reimbursement rates for 2003 have raised concerns and may impact further expansion plans.

Starting a new PET service, or adding to an existing program, is an elaborate process requiring numerous decisions based on regional needs and demands.

WHO NEEDS A PET SCANNER?

Many freestanding outpatient imaging centers, as well as multi-modality, hospital-based, radiology and nuclear medicine departments, have already explored and made decisions to offer PET services. In addition, various medical and radiation oncology groups, as well as multi-specialty medical practices, also have adopted their own PET services, or are in the process of evaluation.

Once feasibility is established, the first challenge ahead is to decide on the type of PET service that is most appropriate for the practice or institution. At the outset, three important decisions need to be made:

1. Dedicated stationary scanner vs mobile services
2. Gamma camera-based coincidence detection system vs a full ring detector system
3. Hybrid system such as a combined PET/CT scanner or coincidence SPECT/CT scanner

Mobile services are suitable if there are concerns about low utilization and procedural volumes. This may be applicable in initiating a program in a highly competitive environment where the risks may be reduced initially by committing to only a few days a week through a mobile service, or in a new market where initial acceptance and utilization may be expected to be low.

Restricted reimbursement for procedures performed on a SPECT gamma camera, modified for PET (coincidence systems), makes this a less viable option. CMS ruled in 2001 that the approvals for new PET applications will be limited to dedicated PET scanners, although legacy applications will continue to be reimbursed with the coincidence cameras. Superior spatial resolution of a dedicated PET scanner is also an important consideration in making a determination between these two choices.

A hybrid combined PET/CT scanner offers the advantage of optimum anatomic/metabolic fusion, but issues such as reimbursement and higher acquisition costs have prevented widespread adoption of this technique to date. Regulatory concerns, such as the need for an additional radiology technologist, in addition to a certified nuclear medicine technologist, also need to be resolved, since this option involves the operation of a CT scanner in addition to the PET camera. The combined PET/CT scanner may be a consideration in sites with low initial anticipated procedure volumes, since the system may be utilized to perform CT scans at times when the PET schedule is light. This rationale may be justified if, in coming years, the price of the combined PET/CT scanner becomes more competitive.

CHOOSING A DEDICATED PET SYSTEM

Choosing a PET system could be either an extremely complex or a straightforward process. If you have a positive experience or a good relationship with the existing supplier, then this may create a positive bias in the decision to add additional scanners to the system. If a different vendor is elected, for whatever reason, the issue of integration of multiple types of systems into the enterprise network is a key consideration.

Ability to network images acquired at various sites to a central reading location was among the criteria considered when Mayur Patel, MD (above), assessed the PET options for American Radiology Services, Baltimore.

Detector Crystal Material. The most commonly used crystal materials in the detector heads are curved NaI, BGO, LSO, and GSO. The traditional systems utilized BGO and NaI crystal material, while GSO and LSO are the two main crystal materials available on the newer generation scanners. The newer generation crystal materials offer improved efficiency and potential for higher image resolution, but at a higher cost. Also to be considered in the evaluation process is the number of detector rings, crystals, and photo multiplier tubes available in the various systems. There are minor variations in the gantry size and the transaxial field of view, which also need to be evaluated.

Transmission Attenuation Correction. The two most popular transmission sources are Cs-137 and Ge-68. Activity per source is variable and is a consideration for exposure and shielding. Cs-137 sources do not require replacement, as opposed to Ge-68, which need to be replaced approximately every 12 months. In addition to replacement frequency, the ease and convenience of replacement needs to be probed.

Image Reconstruction. Filtered back projection and iterative reconstruction are two of the more common options. The time taken for reconstruction will determine how soon the study will be available to the physician for interpretation after scanning is completed. On-the-fly reconstruction, as well as concurrent reconstruction (with acquisition or 4 minutes after completion of acquisition), allows for almost immediate review of the reconstructed images. Three-dimensional reconstruction may be more time-consuming until newer versions of software upgrades are available, and may be a limiting factor to immediate image availability for interpretation. If the reconstruction of images requires several hours in a busy department, it may be practical to allow this to be done overnight, which prevents same day interpretation, and may impact report turnaround time.

The newer generation crystals, with faster scintillation properties and better energy resolution, accommodate 3D imaging at faster speeds without compromising image quality. In large patients, 3D whole body PET acquisition needs careful attention to administered dose to minimize image degradation.

Networking. 10/100 Ethernet and Digital Imaging and Communications in Medicine (DICOM) compatibility are a must in a large multi-site practice. Ability to network the various sites to a centralized reading room was an absolute requirement in our practice for physician efficiency and report turnaround. The ability to network images to one of our hospital-based nuclear radiologists is also advantageous for immediate consultation and "stat" interpretations. The deployment of a wide area network (WAN) enables prompt transmission of images to the interpreting nuclear radiologists at the centralized reading room or to a hospital site.

The two main options available for remote viewing are the use of an additional manufacturer's workstation, or a proprietary third-party viewing platform using DICOM standard transfer. Both are acceptable solutions, although the cost of implementation of the latter solution is significantly less.

Online or offline remote stations need clarification with the vendors since transmission time with online connection is slower and less practical. Availability of prioritized bandwidth for this function within the WAN may minimize the transmission time.

Networking plans also need to address correlative cross-sectional imaging. All PET scans interpreted are correlated with cross-sectional imaging examinations by the interpreting nuclear radiologist. If the CT scans or MRI examinations are acquired within the practice, these are directly transmitted to the workstation at the centralized reading site, via the network. Outside films are either delivered by courier or digitized and transmitted over the network.

DICOM transfer of CT and MRI examinations to the PET workstation is used, which is necessary for purposes of image fusion and radiation treatment planning.

Radiopharmaceutical (FDG) Dose. The fluorine 18-labeled deoxyglucose (FDG) dose needed for the whole body examination varies among the more commonly available systems and is a consideration for reducing patient and operator radiation exposure.

Availability of FDG used to be a limiting factor, but now with the recent proliferation of commercial radiopharmacies, it is not an issue in most metropolitan locations. Reliability is a key consideration. Scheduled examinations occasionally need to be cancelled due to unexpected unavailability of FDG doses, such as with failure of quality control. Flexibility to provide additional doses for add-on emergency cases and for weekend scheduling is an important factor in establishing agreements with the regional radiopharmacy.

Patient Throughput. Estimated total imaging time for a whole body scan should include both the emission and the transmission scans. Patient throughput and projected number of examinations performed in a typical day are an important consideration in feasibility analysis for any site seeking to procure a new PET scanner.

The various vendors reference anywhere from 25 to 75 minutes as the minimum imaging time for a 100-cm FDG whole body scan. These scanning times are, however, subject to such factors as injected dose, uptake time, patient weight, and the desired image quality. Since the actual time is determined by the imaging protocol adopted by the individual sites, it is advisable to ask specific questions when users make on-site visits in order to ensure realistic planning.

Patient throughput may be improved at busier sites by having an extra staff person available to help with the injection of the radiopharmaceutical, completing the patient's history questionnaire, and counseling the patient and family members regarding the procedure. The extra person may be a second nuclear medicine technologist, a physician's assistant, or an imaging aide, depending on the duties assigned, which should be in compliance with regulatory requirements.

Support. Timely response to inevitable operational issues is of critical importance, particularly since quite often, technical support may be needed after the patient has been prepared and injected with the radiopharmaceutical. In these instances, immediate technical support may be needed to salvage the examination without having to reschedule the patient. As far as possible, preventative maintenance and routine software upgrades should be scheduled on weekends or after hours to minimize scheduling downtime. This needs to be prenegotiated within the service agreement.

BEYOND THE TECHNOLOGY

Technological issues are not the only considerations for a facility interested in adopting PET. The success of an individual PET program is ultimately determined by the ability to attract patient referrals and by the quality of service provided to the patient and the referring clinician. In a competitive marketplace, quality service alone is not sufficient to be successful, and needs to be supplemented with a well-structured and targeted marketing program.

Marketing. For an emerging modality such as PET, the most important aspect of marketing is education. Education efforts need to target fellow radiologists, appropriate clinical disciplines, and support personnel.

Fellow radiologists (particularly cross-sectional imagers) need to understand the applications of PET imaging so that in an appropriate diagnostic dilemma, the use of PET scanning is recommended.

The need for education of the clinical disciplines cannot be overstressed. Lack of an adequate education effort may result in clinicians avoiding the modality altogether. The procedure of scheduling a PET scan needs to be simplified and prioritized within the organization. A dedicated phone line and a knowledgeable scheduler are a must. A PET technologist and physician should be accessible to answer any questions or scheduling issues as they arise. All pertinent marketing visits should include a PET-experienced nuclear radiologist who acts as the lead person in the presentation. Addition of a physician to the marketing efforts is expensive, but necessary to assure the success of the program. Presenting at tumor boards, grand rounds, and CME symposiums at the various hospital sites in the catchment area is an essential aspect of physician education.

The future of PET scanning is extremely promising with newer radiopharmaceuticals already in the developmental phase. Ongoing research also suggests future, additional applications with FDG, such as in infectious diseases.

Expanding services to include a well-established PET program is challenging, but with good teamwork and dedicated resources, it can be an exciting and rewarding process.

Mayur Patel, MD, is board certified by the American Board of Radiology and the American Board of Nuclear Medicine. He is director of nuclear medicine at Union Memorial Hospital, Baltimore, and a nuclear radiologist with American Radiology Services.