Overcoming technical challenges in cardiac CT

He outlined several issues that can result in suboptimal CT exams. Issues include patients who have an arrhythmias, in particular atrial fibrillation. Patients who have a high calcium burden or those who had prior revascularization when stenting can face issues with calcium and metal blooming artifact obscuring the coronary arteries or hiding soft plaques. He said patients also come in various sizes and body habitus, which presents specific issues when trying to image very obese patients. Then there are technical considerations with the use of CT contrast and what to do when a patient has impaired renal function. 

All of these issues require a technologists, radiologists and cardiac imagers to understand how to adjust their specific CT systems to overcome these technical problems. As more centers adopt or expand their cardiac CT programs, these technical issues become more important to understand.

Iodine contrast injection considerations in cardiac CT

Proper contrast injection is vital for obtaining accurate cardiac CT images. Hur recommends using larger-bore intravenous (IV) lines and positioning them in a distal vessel, preferably in the arm or forearm, with a large gauge needle. This minimizes the risk of infiltration or extravasation. Safety features on modern contrast injectors can provide warnings and allow for adjustments, reducing the chance of complications.

Extraversion occurs when the IV line comes out of a vessel, or is misplaced, and the contrast is injected under the patients skin, which can lead to compartment syndrome. 

“I always recommend is the larger the bore IV and a more distal placement from the hand and wrist if you can get it into a larger vessel in the arm or the forearm with a large gauge needle, 18 or higher preferably. The reason we recommend that is when we do vascular angiography, we like to inject at a very high rate, usually 5 to 6 ccs per second,” Hur explained.

Adapting CT protocols for patient size, especially in obese patients

Cardiac CT protocols are based on standardized phantoms sizes, but patients come in many shapes and sizes, so the level of radiation dose needs to be adjusted to fit the patient because scanned. Advances in scanner technology, including faster scan times and dose modulation, have improved the ability to adapt to different patient sizes. Properly adjusting voltage and current can help balance diagnostic quality with minimizing radiation exposure, Hur said.

“Being able to dose modulate and add padding I think has improved the ability to potentially scan a larger subset of patients that may have been historically not ideal. So it’s a balance in terms of choosing an appropriate voltage and sometimes we can adjust the current taking into account the patient’s body size and height. And current scanners give you some flexibility,” he said.

Heart rate control for cardiac CT

Maintaining control over a patient’s heart rate is still considered essential in many centers. Beta-blockers are administered to achieve a steady heart rate and minimize arrhythmias, ensuring high-quality images. However, some argue that the higher temporal resolution of modern CT scanners can capture the heart accurately even with arrhythmias, reducing the necessity for strict heart rate control.

Hur said the usage of beta blockers or other anti-arrhythmics are used to keep the heart rate not only at a certain heart rate speed, but also to minimize any ectopy beats, AFib or PVCs to reduce any chance of an arrhythmia impacting the image quality. But with that being said, he said there are now techniques to edit your scan and adjust the rhythm.

“There are still many labs where using 64-slice step and shoot CT. So I think from an education standpoint, it’s really important that we still teach and convey these fundamental concepts of heart rate control. The newer scanners with wide detectors and single heartbeat imaging have definitely been a real advancement and it has given much more flexibility with the heart rate limits,” Hur said.

How to overcome metal artifact in cardiac CT

Metal artifacts from stents, replacement heart valves, endovascular grafts and left atrial appendage occluders have historically been a challenge in CT, especially with older scanners. Heavy calcified plaques also cause a similar streaking or blooming artifact on CT. These artifacts obscure underlaying anatomy and the subtle difference in soft plaques that may be important to understanding a patient’s condition. Newer techniques like iterative reconstruction, sharper kernels and photon counting CT have significantly reduced the impact of metallic artifacts, making it easier to obtain diagnostic images, Hur explained. 

Spectral CT imaging and photon counting CT can help overcome some issues

Dual-energy CT capable scanners and the advent of photon counting CT scanners, which inherently incorporates spectral imaging in all scans, are a promising developments. Hur said photon counting CT allows the differentiation of calcium and certain metals, allowing the imager to dial down or remove these elements from the image to potentially improving diagnostic accuracy and reducing the need for invasive angiography.

Many experts in CT have said photon counting CT systems may become the way of the future, similar to how 64-slice CT systems became a new standard very quickly 10-15 years ago.

CT to better characterize plaque and catch disease much earlier

A new frontier in cardiac CT that will require better technologist training is soft coronary plaque imaging and artificial intelligence (AI) automated analysis. Hur said the future of cardiac CT lies in its ability to characterize plaque composition, differentiate between calcified and noncalcified plaques, and assess perivascular adipose tissue as markers for vulnerable plaque detection and better risk assessments. Hur said this detailed information can play a significant role in preventive cardiology, identifying patients with early coronary artery disease and guiding personalized prevention strategies to reduce the risk of heart attacks and other cardiovascular conditions years before patients become symptomatic.

“So I think the next frontier, if you look over the last 15 or 20 years, we are just scratching the surface with the ability to characterize coronary artery disease, plaques and arteries. Looking for simple stenosis, which in the grand scheme of things I think is a somewhat blunt tool, to now being able to characterize the plaque and describe the perivascular adipose tissue and the composition of very low attenuation plaque. I think it will play an important role in the preventive cardiology sphere in terms of identifying patients early on who may have early forms of CAD, and then from a preventive standpoint, adjusting lifestyle medical therapies to have them prevent the first heart attack,” Hur said.