After remaining relatively stagnant for more than 50 years, the basic design of SPECT cameras has taken a quantum leap: Innovative developers have brought hardware and software improvements to the technology to reduce scan time and allow users to better control the amount of radiotracers given to patients.

Patient images taken with CardiArc HD-SPECT scanner. Images courtesy of CardiArc and Emory University School of Medicine.

In the February issue of the Journal of Nuclear Medicine, Ernest Garcia, PhD, and colleagues from Emory University School of Medicine cite improvements in hardware and software that have spurred dramatic changes within the modality (J Nucl Med, Vol. 52:2, pp. 210-217).

     "The beauty is that you get much higher energy resolution and you can use that to reduce scatter and improve contrast," said Garcia. "The amazing thing is that we are not only getting more efficient machines, but the images are significantly better."

     For cardiac SPECT to compete and succeed in the imaging market, several issues had to be addressed, such as the time to image the heart per study to achieve both optimum patient outcomes and throughput.

Scan time versus dose

     "How do we make a cardiac SPECT study be more on the order of 30 minutes in and out the door as opposed to a couple of hours, which is the case now?" asked Sanjiv Gambhir, MD, PhD, from the departments of radiology and bioengineering at Stanford University Medical Center. "This is an important issue because otherwise echocardiography, cardiac CT, and other technologies -- PET included -- make the future of cardiac SPECT questionable."

     At the same time, cardiac SPECT developers and researchers for years have been trying to build a scanner that can image faster and do so at acceptable levels of radiotracer. "If you can have a very rapid scan with the same amount of radiation injected with a tracer, you can choose to make the scan longer with lower dose," Gambhir said.

     The technology also needed to be easily deployed so it could be located in a cardiologist's office, radiology department, and nuclear medicine practice. The footprint of a cardiac SPECT system had to be compact and not require remodeling of a room to house a complex machine.

System designs

     Among the advancing SPECT technologies is Spectrum Dynamics' D-SPECT, which uses cadmium zinc telluride (CZT) solid-state detectors mounted on nine vertical columns and placed using 90° geometry. The patient is imaged while sitting in a reclining position, similar to a dentist's chair, with his or her left arm placed on top of the detector housing.

     A Stanford University study published in 2009 confirmed the capabilities of the SPECT technology to reduce imaging time for gated SPECT to as much as one-tenth the time of conventional SPECT.

     "You do not compromise on image quality, because at the heart of [D-SPECT] are the solid-state detectors that are very efficient at capturing the counts coming out of the chest and a fundamental redesign from standard gamma-camera technology with multiple pivoting solid-state detectors that surround the chest," said Gambhir, who co-authored the 2009 study and helped develop D-SPECT. "This new design has proved to enhance spatial resolution, while still achieving a decrease in scan time."

     A second SPECT system to offer a new system design was developed by GE Healthcare. The Discovery NM 530c features Alcyone technology, which consists of 19 pinhole collimators, each with four solid-state CZT pixilated detectors.

Simultaneous imaging

     The ability of the 19 collimators to image the heart simultaneously with no moving parts during data acquisition is designed to improve overall sensitivity, and give complete angular data for both dynamic studies and for the reduction of motion artifacts. "It gives you all sorts of advantages for flow, dynamics, and reducing artifacts, if the patient moves," Garcia said.

Images of a 50-year-old man acquired in six minutes at rest and four minutes of stress by Spectrum Dynamic's D-SPECT. The images reveal a large ischemic abnormality involving the apex, anterior, septal, and apical inferior walls indicative of proximal left anterior descending stenosis. Images are courtesy of Spectrum Dynamics and Oregon Heart & Vascular Institute Sacred Heart Medical Center in Springfield, OR.

     CardiArc is developing a cardiac SPECT device with three detectors that include a curved sodium iodide crystal and are set side-by-side to cover a 180° angle. The configuration is designed to help eliminate overlap in acquisitions from adjacent images, and it can reduce the time for a stress scan to as few as three minutes.

     "We can reduce the time for a stress scan to approximately three minutes or can do the scan slower with less tracer," said Jack Juni, MD, CardiArc chairman and CTO and a physician at William Beaumont Hospital. "In initial tests, we have been able to reduce the radiation dose from the tracers by a factor of four."

Small footprint

     With a small footprint of 1 x 1.5 m, the CardiArc system is currently being validated at Emory University, with approximately 40 patients enrolled in the trial so far. Early results indicate that CardiArc detects the same lesions and the images "look at least as good and usually better than regular imaging," Juni said.  Also helping to transform cardiac SPECT, according to the study, is Digirad. The company was one of the first developers to use solid-state electronics and more than two detectors to simultaneously image the heart with its Cardius 3 XPO.

     The system uses 768 pixilated, thallium-activated cesium iodide crystals coupled to individual silicon photodiodes and digital Anger electronics to create the planar projection images used for reconstruction.

     Three detectors are fixed using a 67.5° angular separation, while patients are rotated through an arc of 202.5° sitting on a chair with their arms resting above the detectors. The typical acquisition time for a study is 7.5 minutes.

Enhanced sensitivity

     Siemens Healthcare is offering its IQ-SPECT technology, which features two collimators mounted on the company's conventional dual-detector SPECT cameras, separated by 90°, and rotated around a patient to obtain a 180° reconstruction arc.

     For increased sensitivity and resolution, the fields-of-view of these collimators are most convergent at their center, whereas the convergence is relaxed toward the edge of the field-of-view. The advantage of this approach is that it can be used by Siemens' existing dual-detector systems. Typical myocardial perfusion imaging acquisition times range from four to five minutes.

     Philips Healthcare, meanwhile, offers BrightView XCT, a scalable SPECT/CT system designed for nuclear medicine and nuclear cardiology. The system combines BrightView SPECT and Philips' flat-detector x-ray CT for low patient dose levels and attenuation correction to reduce artifacts and exam times.

Future developments

     Now that much of newer cardiac SPECT technology has been validated, Emory's Garcia said the next step is to develop appropriate imaging protocols to balance scan time and radiotracer dose. "It is becoming more patient-centric imaging," he added. "Instead of having one protocol in one lab, you probably have a few protocols that are geared to reducing radiation and improving images for the patient."

     In recent years, the market has been rocky for cardiac SPECT, as uncertainty over reimbursement and the poor economy have led to less capital spending and delays in equipment purchases.

     "This last year, with the combination of the economy and uncertainty about healthcare at the national level, sales of machines for everybody dropped to almost nothing," reflected CardiArc's Juni. "We are still in that [trend] right now. Physicians are trying to decide whether or not things are stable enough to invest."

Market rebound

     Still, Juni is hopeful that the market might rebound in the next six to twelve months, if there is more word on reimbursement levels for the next three to five years. "Right now, reimbursement is only known with any certainty for 2011," he said. "For 2012, there were some scary numbers floated and no one really knows. That uncertainty is causing a lot of hesitation in the market."

     If SPECT has a future in nuclear cardiology and there is a good return on investment, Garcia believes the technology can also be beneficial in imaging cancer and for other metabolic imaging applications. "We tend to think of molecular imaging more in terms of PET than SPECT, but there are many single photon agents that are very useful for molecular imaging," he added.

     Stanford's Gambhir concurred, saying SPECT, like all of nuclear medicine, isn't all about the hardware; it's also about the tracer. "There are relatively good tracers for cardiac perfusion, like sestamibi and thallium," he said. "What's needed are better ways to do more than just perfusion assessment -- that is, viability assessment and, ideally, a 'one-stop shop' for SPECT where you can get both the coronary and cardiac anatomy, perfusion and viability, all in one shot."

Heart/Lung Ratio Coding

Revised: February 8, 2011

Question:  Is it appropriate to bill for a lung scan, CPT 78580 Pulmonary perfusion imaging, particulate with or without any modifier, for the calculation of the heart-lung ratio during the processing of a SPECT myocardial perfusion procedure, CPT78452?

Answer:  The answer to your question is "no". The CPT code description 78452 is Myocardial perfusion imaging, tomographic (SPECT)(including attenuation correction, qualitative or quantitative wall motion, ejection fraction by first pass or gated technique, additional quantification, when performed); multiple studies, at rest and/or stress (exercise or pharmacologic) and/or redistribution and/or rest reinjection. We call your attention to the "additional quantification" which would include calculations of the heart-lung ratio if obtained.

Myocardial Perfusion Imaging (MPI) Single Day Protocol Versus Multiple Day Protocol

Revised: February 8, 2011

Question

We are performing technetium agent gated SPECT stresses on inpatients and outpatients. Radiologists are interpreting and then reporting out whether or not a rest study is needed. If so, we perform a resting study later on that day or if they are outpatient the next day. Can we charge separately a gated SPECT stress and later in the day, if needed, charge a single study SPECT resting procedure?

Answer

The description of CPT code 78452 is, Myocardial perfusion imaging, tomographic (SPECT)(including attenuation correction, qualitative or quantitative wall motion, ejection fraction by first pass or gated technique, additional quantification, when performed); multiple studies, at rest and/or stress (exercise or pharmacologic) and/or redistribution and/or rest reinjection. Additionally, CPT 78451 is Myocardial perfusion imaging, tomographic (SPECT)(including attenuation correction, qualitative or quantitative wall motion, ejection fraction by first pass or gated technique, additional quantification, when performed): single study, at rest or stress (exercise or pharmacologic).

     We call your attention to the words "Multiple Studies" and "Single Study". There is no distinction regarding performing MPI using a one or two day protocol; nor is there any distinction made for in-patients versus out-patients. Therefore, it is NOT appropriate to code CPT 78451 twice when multiple studies are performed. The appropriate code to use when performing multiple MPI studies (rest/stress, stress/rest, single or two days) is CPT® 78452. When performing a stress study only, then it would be appropriate to code and bill CPT® 78451 once.

A Joint Statement from the American Association of Clinical Endocrinologists, the American Thyroid Association, The Endocrine Society, and the Society of Nuclear Medicine

March 18, 2011

See SNM Press Release 

In an article appearing on December 7 in the online journal PLoS One (2010;5:e15269), Volkow, from the National Institute on Drug Abuse (Bethesda, MD), and colleagues from the Brookhaven National

Laboratory (Upton, NY), reported on a study using PET to measure methamphetamine's organ distribution and pharmacokinetics in the human body. The study included 19 healthy participants (9 Caucasians, 10 African Americans) who underwent 11C-D-methamphetamine PET imaging to measure whole-body distribution and bioavailability as assessed by peak uptake (% dose/cc), rate of clearance (time to reach 50% peak clearance), and accumulation (area under the curve). Methamphetamine was found to distribute through most organs, with the highest uptake (whole organ) in the lungs (22% dose; weight ;1246 g) and liver (23% dose; weight ;1677 g). Uptake was intermediate in the brain (10% dose; weight ;1600 g). High uptake on a per cubic centimeter basis was also found in the kidneys (7% dose; weight 305 g). Clearance was fastest in heart and lungs (6-7 min); slowest in brain, liver, and stomach (75 min); and intermediate in kidneys, spleen, and pancreas (22-50 min). Of note was that fact that lung accumulation of the radiolabeled methamphetamine was 30% higher for African Americans than Caucasians but did not differ in other organs. The authors co cluded that "the high accumultion of methamphetamine, a potent stimulant drug, in most body organs, is likely to co tribute to the medical complications associated with methamphetamine abuse." They spec lated that methamphetamine's high pulmonary uptake could render this organ vulnerable to infections (tuberculosis) and pathology (pulmonary hypertension). They noted that the preliminary findings of higher lung accumulations of methamphetamine in African Americans merit further investigation and question whether this differential could contribute to the less frequent use of methamphetamine among African Americans.

PET brain scans of a methamphetamine user and a control subject.  Courtesy of Jane Koropsak, Brookhaven National Lab.   

----PLoS One

February 18, 2011 - The U.S. Nuclear Regulatory Commission (NRC) is advising healthcare facilities that treat thyroid outpatients with iodine-131 (I-131) to recommend that those patients not stay at hotels immediately after treatment.

      The agency's directive is in response to concerns that thyroid patients typically remain radioactive for a few days following treatment with I-131 and may unknowingly expose other people to radiation.

     The NRC is also asking physicians to provide instructions on how to limit potential radiation exposures to the public following treatment.

      NRC regulations allow I-131 patients to be released following treatment when the radiation dose to third parties is not likely to exceed 500 mrem. The guidelines assume the dose would apply primarily to a patient's family or other caregivers during the first few days the patient is at home after treatment.

See NRC Press Release 

JNMT: Technologist Radiation Exposure

A lead barrier can reduce radiation dose to technologists by about two times during nuclear medicine procedures, lowering external radiation doses to technologists within permissible levels, according to a study published in this month's Journal of Nuclear Medicine Technology.

     The study, led by Bircan Sonmez, MD, from the department of nuclear medicine, Karadeniz Technical University, Trabzon, Turkey, used a Geiger-Müller detector to measure dose rates to technologists at various distances from patients behind a lead shield and determined the average time spent by technologists at these distances. Deep-dose equivalents to technologists were obtained.

     The nuclear medicine procedures considered by the researchers were thyroid scintigraphy performed using 99mTc pertechnetate, whole-body bone scanning performed using 99mTc-methylene diphosphonate (MDP), myocardial perfusion scanning performed using 99mTc-methoxyisobutyl isonitrile (MIBI), 201Tl (thallous chloride) and renal scanning performed using 99mTc-dimercaptosuccinic acid (DMSA).

     The measured deep-dose equivalent to technologists per procedure was within the range of 0.13 to 0.43 uSv using a lead shield and 0.21 to 1.01 uSv without a lead shield. For a total of 95 clinical cases, effective external radiation doses to technologists were found to be within the permissible levels, according to Sonmez and colleagues.

     Doses to technologists varied significantly for different diagnostic applications, the researchers found. 99mTc-MIBI myocardial perfusion scans imparted higher doses (1.01 mSv without a lead shield and 0.43 mSv with a lead shield) to technologists than did the other types of scans. Although 201Tl myocardial perfusion scans were applied in the same manner as 99mTc-MIBI, 201Tl yielded lower doses to technologists (0.23 mSv without a lead shield and 0.16 mSv with a lead shield).

     The contributions of the patient positioning dose to total dose (without a lead shield) were approximately 18 percent, 31 percent, 14 percent, 13 percent and 9 percent for 99mTc-MDP whole-body bone scans, 99mTc-pertechnetate thyroid scans, 99mTc-DMSA renal scans, 99mTc-MIBI myocardial perfusion scans and 201Tl myocardial perfusion scans, respectively.

     The authors noted that even without a rotation of the work force, and even with a major increase in the number of patients, the annual dose to individual technologists would not reach the annual limit (20 mSv) specified by the International Commission on Radiological Protection.

FIGURE 1. Doses to Technologists per Nuclear Medicine Procedure.

---- HealthImaging.com

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