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Inside the ASNC SPECT Imaging Guidelines

Posted on: 10.18.19

The field of nuclear cardiology has expanded greatly over the last few years, prompting an update of the ASNC SPECT Myocardial Perfusion Guidelines.

Updated guidelines were published in May 2018 and include newer generation cameras, processing techniques, and key topics such as radiation reduction. These guidelines have also been endorsed by SNMMI. A core tenet of the guidelines is giving clinicians a review of the available imaging tools in nuclear myocardial perfusion imaging and focusing attention on choosing the right test for the right patient at the right time.

We caught up with Karthik Ananthasubramaniam, MD, one of the section lead authors of the guidelines to discuss their process and what the new guidelines mean for physicians. He is part of a team lead by Dr. Sharmila Dorbala that includes clinicians, physicists, and individuals who use SPECT on a daily basis.

Dr. Ananthasubramanium says that, while the essential principles of the original 2010 guidelines remain intact, this update was about providing a detailed update on the modern equipment and techniques that physicians and technologists use today. SPECT remains the dominant modality for stress testing, with over 8.5 million studies performed annually.

ASNC SPECT Imaging Guidelines

With physicians all across the world using SPECT as a frontline testing option, it’s essential that it is done the right way. Here are some of the key updates in the new guidelines:

The guidelines are easier to read

As Dr. Ananthasubramaniam describes, one of the key goals of the committee was to make the guidelines more visually appealing to read. This is one way that they can be made more accessible and useful to those who need them.

While the 2010 version had some visual aids, this new 2018 update contains around 25 to 30 visual aids, most of them in color. In this way, the new documentation seeks to reduce reader fatigue and make information more easily digestible.

For example, quality control is a vital aspect of the role of technologists. The team behind the updates wanted to clearly highlight how quality control works, so they included images to demonstrate this visually. Numerous illustrations of clinical cases and illustrations and pictures to demonstrate artifacts in SPECT convey difficult concepts in a visually appealing way to enable the reader to understand the concepts easily

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Focus on new camera technology

Nuclear imaging has principally used the same technology for over 50 years. However, the last decade has seen the release of brand new camera designs and imaging technologies.

Significant camera hardware advances from Anger-based camera technology to solid-state nuclear imaging have been highlighted in detail in these new guidelines. Solid-state camera systems provide more advanced technology and benefits over Anger cameras such as being cardiac focused with higher resolution, sensitivity, and higher quality images.

The guidelines have been updated to show the physical principles of these cameras and explain what they can do. The guidelines for how to read images from these newer cameras are a vital part of this explanation.

A complete review of suggested protocols and radioisotope dosings to use for cardiac SPECT imaging is available in the new guidelines. The newer solid-state cameras are capable of acquiring high-quality diagnostic images at much faster speed and lower isotope doses – cutting back radiation and speeding up the test for the patient.

Newer aspects of image interpretation

Attenuation correction to correct for decreased counts is yet to be widely adopted for SPECT image interpretation. This is the mechanism through which soft tissue artifacts are removed from SPECT imaging. The new guidelines have a focussed section on how clinicians should use attenuation correction for interpretation of SPECT scans.

The new guidelines highlight how attenuation correction should be performed, what artifacts should be avoided, and how they can be recognized and corrected. Ultimately, the goal is to reduce the impact of attenuation in order to provide images that are more uniform and allow for higher reading confidence.

Patient-centered imaging

There is an entirely new section in the updated guidelines that covers patient-centered imaging. ASNC has strongly advocated for tailoring of imaging for the individual patient and reducing radiation. While a one-test-fits-all approach may simplify clinical decision-making, it is suboptimal for patient care. From their guidelines:

“The key principles of the desirable individualized imaging approach include justification, that is, appropriate testing, and optimization, i.e., performing the test in an ideal manner.”

The focus should be on the patient rather than the protocol and performing the test in a way that will be best for the individual. This section of the guidelines includes strategies for reducing the use of radiation and guidelines for choosing the correct protocol. It all ties back to the “right test for the right patient” message that was central to the update.

Development and use of guidelines

The guidelines were developed over a period of time and underwent updates as they went through rounds of peer reviews and the committee. In this way, the process to develop the guidelines was rigorous.

Dr. Ananthasubramaniam was excited to see the results of this team work of experts go live. The ASNC SPECT guidelines form the backbone of guidance to physicians and technologists and serves as an updated reference for many questions. He trains many cardiology fellows per year and uses these guidelines as the main document from which to train them. It is his belief that the new guidelines are an important document that will help clinicians to perform better SPECT imaging and ultimately, help patients too.

Get the bonus content: Patient-Centered MPI Guidelines

Today’s SPECT technology effectively allows for exceedingly low radiation dose imaging and personalized imaging protocols. The updated SPECT guidelines look into the future by discussing the promise of myocardial blood flow quantitation with the advent of the newer camera systems. By leveraging the new advancements, the revised guidelines promote a more patient-centric and personalized approach that contributes to higher-quality imaging and more meaningful results.

The medical community considers the update a significant move toward the standardization of SPECT MPI and one that will ultimately allow them to provide patients with the highest level of customized care.

The role and future of SPECT

Dr. Ananthasubramaniam believes the role of SPECT is expanding. While PET is making some inroads, SPECT is the predominant technology driving cardiology imaging today worldwide.

For example, in the past, SPECT was only for coronary artery disease, but it is now making its way into other pathologies. Now you are seeing SPECT used for Cardiac Amyloidosis imaging too.

Overall, there continues to be new technology and new protocols being developed in the SPECT space. Suggestions for how to improve image quality by incorporating specific software such as resolution recovery even with existing Anger cameras are discussed in detail.

The updated guidelines are expected to be valid for quite some time to come as they also include insights into where SPECT is heading. For example, new technology that is not yet fully developed is discussed, such as blood flow quantification.

All in all, the future of SPECT looks bright with much more to come.

How is patient obesity affecting cardiac imaging?

Posted on: 05.16.19

Obesity rates in the United States are the highest in the world and a growing health concern. In fact, according to data published by the Centers for Disease Control, 67% of men and 62% of women are overweight. Thirty-four percent of women and 28% of men could be further classified as obese. It’s a contributing factor in numerous diseases like Type 2 diabetes, cancer, stroke, and coronary artery disease.

Because obesity puts patients at greater risk for a host of other medical conditions, they’ll ultimately require more tests and scans during their lifetime in comparison to leaner patients. When it comes to nuclear imaging, obese patients and the unique challenges their weight presents can further hinder an accurate diagnosis and an optimal treatment plan.

How to perform cardiac imaging on obese patients

Imaging and obesity-related challenges

Consider something as simple as diagnostic testing. Most nuclear cameras are designed to accommodate the standard, ideal-weighted patient. With obesity rates climbing at an alarming rate, physicians need to think about whether their equipment can adequately serve this growing population.

Many of today’s SPECT cameras still have a maximum weight capacity of 250-300 pounds. This standard feature can make imaging impossible for larger patients and can put both the patient and the technologist at risk.

For example, an obese patient will have difficulty getting up on, positioning and balancing themselves, and remaining still as they lay on a standard imaging table. They’ll also have to turn over or step down from the table, which could be equally as dangerous. Obese patients have a different center of gravity, which is a significant safety concern that needs to be addressed.

Some SPECT cameras, like the Digirad X-ACT+, utilize the more patient-friendly, seated position, which all but eliminates the patient’s risk of injury from climbing up on, balancing, turning, and stepping down from a supine-positioned table. It also has a maximum weight allowance of 500 pounds, a larger gantry for ingress and egress, and handrails for support.

Orbital space, girth, and field of view

Another issue is reduced orbital space. If the distance between the patient and the detectors is not sufficient, the detectors may not be able to rotate properly. Especially when imaging larger patients, the risk of truncation occurs if the detectors are not able to clear the distance, or cover the girth.

Many of today’s SPECT cameras also have a fixed detector design, which challenges the ability to position the heart of an obese patient in the “sweet spot.” A leaner patient’s heart is more likely to be ideally positioned because today’s cameras are designed for their average body type.

With any size patient, a technician should be able to center the heart in the field of view with relative ease, like with the Digirad X-ACT+ camera. Once the patient is seated, the chair can be moved forward and backward and from left to right in order to optimally position the heart inside the field of view and with enough distance from the detectors.

Attenuation, radiation, and scan time

Images with excessive attenuation and scatter are also more prevalent with obese patients. Dense breast tissue, for example, in both male and female patients, makes it more difficult to acquire accurate quantitative information. Attenuation correction has significant diagnostic value for all patients, but especially obese patients. With it, image clarity and quality are improved, which can result in fewer false positives and fewer unnecessary cardiac catheterizations.

Radiation dosage and scan times for obese patients can be an issue too. While there are standard imaging protocols, they were created for an average weighted patient. Dosage calculations are higher and scan times are longer for obese patients, but those estimated amounts can miss the mark. A low estimate compromises the quality of the images and a high estimate unnecessarily increases the radiation burden to the patient.

The Digirad X-ACT+ camera not only performs attenuation correction with a radiation dose of less than five microsieverts, it also uses TruACQ Count Based Imaging™ software to calculate dosing and scan times. Without the guesswork, technologists can proceed with confidence and ultimately work to deliver higher quality images.

Many of the imaging problems that accompany obese patients can be overcome with the right equipment and software. In reality, though, technicians and cardiologists will simply work with the equipment they have to do the best job they can. At Digirad, we believe that every patient deserves the highest quality of care, regardless of their weight.

Digirad can help

The fact that an imaging system can easily accommodate obese patients may not be the sole reason you choose a camera. However, when that benefit is paired with state-of-the-art technology that can help deliver a higher level of quality of care for a broader group of patients, it’s hard to ignore.

Are all SPECT MPI cameras the same?

Posted on: 05.13.19

It’s safe to say that SPECT is a well-established and widely used modality in diagnostic cardiac imaging. While some cameras may be younger than others or have more bells and whistles, is it also safe to say that they’re generally the same?

With rapidly advancing technology, the real question comes down to how; How much more convenience and comfort does a particular model provide? How much higher is the image clarity and quality? How much faster is the scan time and how does that affect the radiation exposure to the patient? Overall, how much difference do these answers make in the quality care you provide?

Anger vs. solid-state technology

The biggest distinction between a SPECT camera is its base technology, which can be either Anger or solid-state. Anger technology gamma cameras use vacuum tube photomultipliers (PMTs) and hygroscopic sodium iodide (NaI) crystals. These cameras were designed by Hal Anger more than 50 years ago. Although the technology is antiquated, there are a surprising number of Anger-based imaging systems still in operation today.

Solid state, on the other hand, is the more advanced technology that uses a pixilated detector. It provides benefits over Anger-based systems including, its compact and lightweight design, higher quality images, enhanced patient experience, and the ability to be employed in both fixed and mobile configurations.

For example, one of the most noticeable differences between solid-state and Anger is the size of the detector heads. Anger’s PMTs and NaL crystals require a significant amount of space. The solid-state detectors, however, are a fraction of Anger’s size and contribute to its more ideal, compact feature. The weight of a solid-state detector is also over 600% lighter than that of an Anger head too.

Solid-state technology

There are two types of solid-state nuclear imaging technology, direct and indirect conversion. Direct conversion uses cadmium zinc telluride (CZT). When the crystal absorbs a photon, it creates an electric charge directly, hence the term direct conversion. Direct conversion is effective but the manufacturing cost of CZT can be expensive.

Indirect conversion uses cesium iodide (CsI) with a photodiode. When a photon comes in contact with the crystal it produces light, which is converted to an electronic signal. This process is faster and the manufacturing cost of CsI detectors is significantly less than that of CZT.

With Digirad’s technology, each solid-state gamma detector is comprised of thousands of individual detector elements, or pixels. Each pixel is isolated from the other. When a scintillation event occurs on a particular crystal, its exact location can be quickly and accurately identified, making the detector substantially faster and more accurate.

Solid-state technology allows for lower levels of radiation to be used in imaging. And, attenuation correction can be performed using the same detectors for both the transmission and emission in a single sitting, thereby reducing scan time.

Attenuation correction

On the surface, many solid-state SPECT camera systems may look similar. But, if you compare their individual design, functionality, and features more closely, you’ll see that they can differ significantly.

For example, the Digirad X-Act+ camera uses CsI photodiode and employs triple head cardio-centric imaging. The Spectrum Dynamics D-SPECT camera uses CZT and relies on high efficiency moving column detectors. Both CsI and CZT crystals are effective, and both acquisition methods are fast imaging.

The distinguishing features are those that are absent. Although both types of detector geometries mentioned are efficient, moving columns have a higher potential for truncation.

Consider the fully integrated micro-low dose fluorescence attenuation correction feature of the X-ACT+. The D-SPECT imaging system does not offer any built-in process that identifies and corrects for soft tissue artifacts in their SPECT images. Given the fact that attenuation correction results in higher reading confidence, improved diagnostic accuracy, and a lower incidence of false positive studies, Digirad’s methodology is able to offer a significant improvement from a reliability, exposure, and cost standpoint.

In the end

All SPECT cameras are not the same. Whether it’s the number of detectors, technology, maximum weight supported, or the additional features provided – your best decision will be made by weighing the advantages and disadvantages of each model and manufacturer.

What is SPECT imaging and how does it work?

Posted on: 03.07.19

SPECT stands for single-photon emission computerized tomography. In layman’s terms, it’s a type of non-invasive nuclear imaging test that allows your doctor to see how well your internal organs are functioning. It uses a radioactive substance and a special gamma camera to create 3-D pictures of your organs at different angles.

Gamma cameras like the Digirad Cardius® 3 XPO and the X-ACT+ employ advanced solid-state technology that uses a silicon-based photodiode, coupled with cesium iodide (CsI). The technology not only offers better sensitivity and high energy resolution, but it also makes the camera smaller in size than a traditional MRI machine. And, with their open and upright design, they’re much more ergonomic and patient-friendly.

While an x-ray takes a picture of what your organs look like at a given point in time, a SPECT image shows blood flowing to and from the heart or blood flow restrictions due to narrow or blocked arteries. It can also be used to evaluate brain and neurological conditions and bone disorders.

In what cases is SPECT imaging ordered?

Not only can SPECT imaging capture how well your heart is performing, but it can also help diagnose disease processes that may be underway, including narrowing of the arteries, clogged arteries, identifying scar tissue due to heart attacks, or evaluating the success of surgeries like bypass surgery.

How does SPECT imaging work?

SPECT scans use a radioactive material called a tracer. The tracer is injected intravenously and mixes with your blood. As your blood moves through your body, it’s “taken up” or absorbed by your living heart muscle.

The Digirad Cardius® 3 XPO and the X-ACT+ allow for patients to be imaged in a comfortable seated position but other gamma cameras require you to lie down on a table. During the scan, the SPECT camera rotates around you. It picks up signals from the radioactive tracer, which are then converted to 3-D images by a computer.

When you undergo a nuclear stress test, a SPECT scan will be taken while you’re exercising and again when you’re at rest. The comparison of the images will allow your physician to evaluate blood flow under different levels of exertion.

Your images may show different shades of color that will indicate which areas of your heart absorbed more of the radioactive tracer and which areas absorbed less. A normal test result indicates there is sufficient and unrestricted blood flow to your heart, while an abnormal result means your heart’s blood flow is insufficient. Once your physician reviews your images, you’ll meet to discuss the results and any necessary treatment plan.

Example of SPECT imaging heart scan

What are the risks of SPECT imaging?

SPECT imaging is generally safe and most patients can go back to their normal activity right away. The amount of radioactive material injected into your bloodstream is small and your body will expel it through your kidneys in 24 to 72 hours. Be sure to drink plenty of water for a few days following the procedure.

If you are pregnant, think you may be pregnant, or are a nursing mother, be sure to notify your doctor prior to the scan. The test uses a low-dose of radiation, which is contraindicated for pregnant women. Nursing mothers may be advised to wait additional time before nursing again so that your body can excrete the tracer.

Patients may also have an allergic reaction to the radioactive tracer, although it’s uncommon.

SPECT imaging is a popular, cost-effective, and safe method of evaluating your heart and diagnosing disease. While you may be a little anxious, be assured that the scan is painless and it provides important clinical value to your physician.

What’s next for SPECT with Kathy Flood

Posted on: 02.14.19

After several years of reduced reimbursements and decreasing volumes, SPECT imaging has stabilized and is primed for growth. Digirad recently spoke with Kathy Flood, CEO of the American Society of Nuclear Cardiology, to get her viewpoint on SPECT imaging and where the modality is headed.

“Volumes are not dropping as dramatically as they were in the past,” she said, “one factor in this is that people are recognizing the value of nuclear cardiology, and secondly we’re seeing increases due to the implementation of appropriate use criteria.” ASNC has supported their members with increased education on appropriate use, which is helping. But, looking down the road, the applications for SPECT nuclear are beginning to grow.

SPECT Applications for Cardiac Amyloidosis

One of those new applications involves cardiac amyloidosis. In the past, a cardiac amyloidosis diagnosis could only be confirmed with a cardiac biopsy. And still, there was no available treatment. Now, a nuclear scan using technetium-99m pyrophosphate (Tc 99m PYP) is almost as effective as a cardiac biopsy.

With treatment drugs in the pipeline, there’s an exciting opportunity for nuclear imaging to play a significant role in both the diagnosis and management of the disease.

The availability of new treatments has heightened the importance of awareness, early diagnosis, and accurate typing of cardiac amyloidosis. In response, ASNC is working on an educational campaign that focuses on PYP imaging for patients with suspected cardiac amyloidosis.

New Educational Initiatives

ASNC’s annual Nuclear Cardiology Today Event, scheduled for April 12-14, 2019, will include a practical workshop on cardiac amyloidosis where not only nuclear cardiologists, but also referring physicians can learn about the disease.

The half-day, case-based program will address the diagnosis and management, tackle the challenges of disease presentation, discuss the role of various imaging modalities in the diagnosis, and give an overview of current and emerging treatments.

Cardiac amyloidosis is considered a rare and potentially under-diagnosed disease. One of the contributing factors is that its symptoms closely resemble heart failure. As statistics say that about 30% of heart failure patients have been misdiagnosed and that heart failure is the number one disease state where Medicare spends money, that equates to a lot of patients.

“Our goal is to make our members and referring physicians aware of cardiac amyloidosis, about the role of nuclear cardiology, and how to provide high-quality imaging around that for decision making and treatment,” said Flood.

ASNC also plans to offer more hands-on simulation opportunities at their meetings so that members can network with experts in their field, better understand how they’re performing nuclear cardiology, and learn how they can improve. Taking those experiences back to their labs will help them provide the best images for their patients.

Investing in the Next Generation

Looking ahead, ASNC is intent on making sure their members have what they need, but they’re also making investments in the new generation. “We’re working to put together programs specifically for the cardiology fellowship training programs. We want to be able to either help supplement some of the nuclear education they receive, or if they don’t receive any, be able to direct them to ASNC,” said Flood.

SPECT remains the most common procedure in nuclear cardiology, but the younger generation tends to focus on the newer modalities, like Cardiac CT. Once they graduate, they’re often unable to use this knowledge in practice because the new modalities are not as widespread in the field. That’s when they look back and wish they would have spent more time on SPECT imaging.

“We’re trying to fill that void as we move forward over the next couple of years so we have more programs and touch points with fellows in training so they can get just as excited about nuclear, too,” said Flood.

2018 ASNC SPECT MPI Imaging Guidelines Issued

Posted on: 07.19.18

Recent advancements in SPECT Myocardial Perfusion Imaging prompted ASNC to issue updated SPECT guidelines, which were published on May 25, 2018.

The highly anticipated new guidelines, ASNC Imaging Guidelines: Single Photon Emission Computed Tomography (SPECT) Myocardial Perfusion Imaging—Instrumentation, Acquisition, Processing, and Interpretation, incorporate the most up-to-date information and advancements in SPECT technology since the previous 2010 ASNC SPECT guidelines were published.

Today’s SPECT technology effectively allows for exceedingly low radiation dose imaging, myocardial blood flow quantitation, and personalized imaging protocols. By leveraging the new advancements, the revised guidelines promote a more patient-centric and personalized approach that contributes to higher-quality imaging and more meaningful results.

The medical community considers the update a significant move toward the standardization of SPECT MPI and one that will ultimately allow them to provide patients with the highest level of customized care.

The new guideline features updates on novel hardware, collimators, and CZT scanners, as well as newly added sections on reduced count density reconstruction techniques, SPECT myocardial blood flow quantification, stress-first/stress-only imaging, and patient-centered myocardial perfusion imaging.

The guidelines were endorsed by the Society of Nuclear Medicine and Molecular Imaging and published in the Journal of Nuclear Cardiology. You can view and download the new guidelines from ASNC’s website and read the official press release here.

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