CT, MR and the Current State of Technology for Cardiac ImagingPosted on: 08.08.19
Technology and the modalities that drive diagnostic cardiology continue to see innovation and development. New technologies and advancements in cardiac imaging will have a direct effect on both cardiologists and patients as they move mainstream. In this post, we’ll look at what is happening with cardiac imaging technology:
CT technology for Cardiac Imaging
One of the significant developments with CT Technology is CT with FRR. Fractional Flow Reserve (FRR) is traditionally an invasive, guide wire-based procedure allowing clinicians to accurately measure blood pressure and flow through a specific part of the artery. With CT, it is non-invasive.
A potential advantage of using FRR is that when combined with the CT, the images are powerful enough to identify whether a vessel needs medical intervention. Joel Sauer, Executive Vice President of Consulting at MedAxiom, has spoken with cardiologists who describe this technology as a “game-changer.”
Up until now, a decision to stent or not was generally based on the vessel being blocked above a certain percentage, however, this did not guarantee the procedure was the best course of action. For example, perhaps a vessel is clogged but isn’t the source of the issue for the patient, or a vessel might have build-up but is not worth stenting because muscle around it is already dead. FRR with CT can identify these situations and allow for a more effective treatment plan.
Recent conference sessions on CT-FRR have discussed how the technology might now be mature enough to routinely use with patients. The Centers for Medicare and Medicaid Services (CMS) as well as private insurers have been approving reimbursements, driven by clinical evidence showing the technology can reduce the need for diagnostic angiograms or allow early discharge of patients who present in the emergency department (ED) where FFR-CT can definitively rule out severe ischemic heart disease.
The technology is not only useful for interventional planning, but for detecting and tracking disease early. This can mean that patients have the opportunity to reverse plaque formation and avoid surgery. The challenge will then be to keep them compliant for the years to come, another area in which CT has a role to play. Physicians can track patient condition using CT and use it to show where improvements have been made as a result of lifestyle changes, or where improvements could be made.
Challenges with Cardiac CT
Consequently, the technology has been slow to be adopted by medical practices. Part of this may be that the datasets have to be sent to a single provider, HeartFlow, via the internet. This is because they host the super-computing power required to run the powerful algorithms behind FFR-CT technology.
Another potentially limiting issue is that the scans are often read in the radiology department rather than a cardiologist. This requires extra training for radiologists for whom heart imaging may be a new field of study.
One thing that might spur further adoption is that use of FFR-CT can reduce the need for further testing. For example, where a patient has undergone stress testing and still has chest pain, a diagnostic cath would usually be ordered. FFR-CT can reduce the need for a cath where it won’t make any difference for the patient if it is used as the next step.
MRI technology for Cardiac Imaging
An MRI cardiac stress test is showing promising results, both for determining heart function and for predicting which cases are potentially fatal.
Cardiac magnetic resonance (CMR) has potential as a non-invasive alternative to tests such as catheterizations or nuclear imaging. In a study appearing in JAMA Cardiology, senior author Robert Judd, Ph.D., co-director of the Duke Cardiovascular Magnetic Resonance Center says:
“We’ve known for some time that CMR is effective at diagnosing coronary artery disease, but it’s still not commonly used and represents less than one percent of stress tests used in this country.
One of the impediments to broader use has been a lack of data on its predictive value — something competing technologies have,” Judd said. “Our study provides some clarity, although direct comparisons between CMR and other technologies would be definitive.”
Some barriers to further adoption of stress CMR include the availability of good-quality laboratories, a lack of data on outcomes and the necessity to exclude patients who cannot undergo magnetization. There’s also a similar issue to CT in that not everyone who can read nuclear imaging can read a CMR.
It is likely that many technologists will need special training to be able to produce the quality images that are needed. The study mentioned here provides a good starting point for head to head studies with other modalities, particularly to determine whether it is worth hospitals investing more in technology and training.
Cardiac SPECT and PET
A clear advantage of nuclear SPECT is the availability of imagers and the overall cost of the procedure. When you compare SPECT to CT, it is more cost-effective and takes a lot less time. The fastest CT procedures (on top-of-the-line machines) generally take 45 minutes, whereas SPECT takes 30 minutes or less. Gamma technology has reduced imaging times for SPECT from 15-20 minutes to 2-4 minutes.
SPECT is utilized significantly more often than PET, particularly due to the high cost of the generator-based PET MPI agent and PET imaging systems..
There are a few noteworthy trends with SPECT and PET. In particular, there has been a marked decrease in numbers since the mid-2000s, despite most risk factors for cardiac events still being present. Secondly, there has been a decrease in abnormal test results over time.
There are a myriad of reasons indicated for these trends, such as the emergence of Appropriate Use Criteria in 2005 and more patients who can tolerate exercise undergoing stress testing without nuclear imaging as a first option.
In other developments, nonperfusion cardiac imaging is gaining ground. Here is an extract from a Journal of Nuclear Cardiology article, written by George A. Bellar:
The acceptance and growth of nonperfusion cardiac imaging applications are vital in widening the offerings of nuclear cardiology going forward. Already, much activity has been ongoing in validating the worth of F-18-flurodeoxyglucose (FDG) imaging for detecting and quantitating focal inflammatory lesions in patients with sarcoidosis.13,14
From 8 published studies, the pooled sensitivity and specificity values for detecting cardiac involvement with sarcoid were 89% and 78%, respectively. Combining MPI with FDG imaging could even enhance the accuracy of detection of sarcoid granulomas in the heart. Even combining PET with MRI for showing areas of delayed hyperenhancement in areas of decreased perfusion without inflammation could be an early manifestation of cardiac sarcoid.
Bottom line – we’re seeing vast advances in the quality of imaging from all technologies and with that, the ability to accurately diagnose. However, each technology has strengths and weaknesses.
There’s the amount of time taken and, therefore, limitations placed on patient throughput. Then there are the relative costs and whether approval can be gained from CMS or insurance companies. In some cases pre-authorization is required.
Most of the time, it comes down to training and availability. Some of the more recent cardiac imaging technologies are not yet widely available or require additional training of technologists. Overall, it will be helpful to see more direct comparisons between the different modalities and their diagnostic qualities.
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.
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.