CTA coronary angiogram

The new technologies emerging in the clinical setting include fractional flow reserve (FFR)-CT, CT perfusion imaging and coronary plaque assessment.


Beyond Computed Tomography

Since introducing the standard 64-slice CT scanners, today’s cardiac computed tomography imaging can examine a patient using a very low radiation dose to obtain a cardiac scan not exceeding 3 mSv.  This is only possible through the technological advancements of more sensitive detectors and faster gantry speed rotation.  Also, image reconstruction software enables low radiation dose scans to produce in-depth resolution diagnostic quality images compared to using high x-ray doses in older cardiac CT scanners.

The new technologies emerging in the clinical setting include fractional flow reserve (FFR)-CT, CT perfusion imaging and coronary plaque assessment.  These breakthroughs will bring CT beyond the anatomical evaluation to allow physiological evaluation without the patient undergoing nuclear perfusion scans or invasive diagnostic angiography. Especially the more advanced automated visualisation software used in an invasive examination in the cath lab where an FFR is performed and intravascular ultrasound imaging is used to evaluate the lesions.  However, CT offers a non-invasive way to achieve these same assessments.

FFR-CT has been approved by the US Food and Drug Administration (FDA) for the non-invasive hemodynamic assessment of the entire coronary tree.  This imaging modality can create a 3-D model of the coronary arteries using colour-codes based on computational fluid dynamics.  These colour codes will show low flow areas which are correlated to the coronary lesions.  The aim is to identify lesions that may lead to ischemic chest pain or a heart attack.  However, the FFR-CT technology can take several hours to return a result.  In the future, the processing time will be reduced and FFR-CT will be broadly used in the clinical setting.

CT used in Prevention and Risk Assessment

Today, modern CT machines have the potential for serial imaging due to very low-dose radiation dose not exceeding one mSv during the scanning of the patient.  Therefore, the older 64-slice CT systems need to be upgraded with more sensitive detectors, including the advanced image reconstruction software.

CTCA will be the leading imaging modality to identify early coronary disease

These new coronary-CT scanners aim to identify early plaque before it leads to advanced coronary disease. The stress testing does not show early plaque until you have a reasonable amount of coronary disease compared to CT scanning.  CT scanning will allow the patient to personalise the treatment plan to prevent a heart attack.  Furthermore, cardiac-CT as a risk assessment tool already sees growth is with calcium scoring.  Numerous clinical trials have shown a correlation between the amount of calcified plaque in coronary vessels and a patient’s risk for a heart attack. CT calcium scoring can also be used to convince patients to go on statin therapy and calcium scoring to be performed at least every five years.

New Areas of Cardiac CT Usage

The latest CT cardiac scanners can determine structural heart evaluation and procedural planning.  In addition, these scanners are also able to do precise imaging based on advanced visualisation software.  These new technologies will bring state-of-the-art of cardiac imaging in transcatheter aortic valve replacement (TAVR). In addition to left atrial appendage (LAA) occlusion and transcatheter mitral repair.

Modern CT Scanner Technology

The most significant advances in CT scanners over the past decade have been delivering low dose radiation to the patient.  This can be achieved by upgrading the older CT scanners to high-slice systems, including faster gantry speeds to freeze cardiac motion.  Furthermore, modern CT scanners can perform a complete anatomical coverage in one rotation.  The problem with the 64-slice scanners was that it usually took two rotations to image the heart.  New scanner technology will lower CT cardiac exams to 3 mSv or below.  However, some centres are already performing routine cardiac CT exams one mSv or below using the newest scanners and image reconstruction software.

Also, the advancements in the detector resolution will increase the image sharpness and resolution by 0.2 mm. This will enable defining the smaller structures of the plaque composition and stents inside coronary vessels.  In addition, to the volume spectral CT technology to improve tissue characterisation, small lesion detection and metal artefact reduction.

Another improvement to CT scanners is the Whisper Drive technology to allow high-speed scans to produce diagnostic imaging of the heart in one heartbeat. This is possible by using a high-speed x-ray tube that circles the patient up to five times per second.  Also, a 30-degree bidirectional gantry tilt capability enables angled scanning to avoid dosing radiosensitive organs.

Furthermore, the 80-detector row (160-slice) system is designed to perform whole-body imaging and volumetric scanning.  These improvements are found in the high-end CT scanners to enable a superior patient experience.  They can provide faster reconstruction speeds of up to 50 images per second at full resolution.  In addition, to optimises workflow and patient comfort with thin slices at 0.5 mm and a 78-cm bore.  Moreover, these CT scanners use SURESubtraction and Single Energy Metal Artifact Reduction (SEMAR) and can be installed on the 40 to 80 to 160 slices.  These technological advances in CT machines enable faster scanning speeds that allow to perform sedation-free pediatric exams and freeze cardiac motion.

PET/CT Heart Scans

Positron emission tomography (PET) scanning combined with Computed Tomography Coronary Angiogram CTCA is on the horizon to detect cardiovascular diseases.

A PET scan uses a small dose of a radiopharmaceutical imaging agent injected into the patient before PET scanning. As with CTCA, PET imaging involves a scanning machine to obtain the images.  The cardiologist and radiologist then interpret the images to evaluate biological functions, such as blood flow and glucose metabolism of the heart.

Conclusion

Fractional flow reserve (FFR) derived from data obtained during the computed tomography coronary angiogram provides critical information to the cardiology medical team without exposing the patient to unnecessary risk. Previously, FFR data was acquired by subjecting the patient to an invasive cardiac catheterisation.  During this procedure, a reduction in contrast agent was used and gave improved diagnostic imaging.  However, there are several problems in the routine use of FFR in the cardiac catheterisation lab. First, fractional flow reserve CT values can be acquired using resting 3-D coronary CTA images from computational fluid dynamics.  This technology has been demonstrated from several clinical trials that Fractional flow reserve CT is a more superior diagnostic imaging modality than the traditional coronary CTA in detecting coronary artery disease. Therefore, the future of Fractional flow reserve CT will depend on the interpretation of data from artificial intelligence and its evaluation of ischemic heart disease.  Furthermore, non-invasive diagnostic imaging identifies the significant lesions to distinguish between patients who can safely avoid invasive coronary angiography and patients who require revascularization. Artificial Intelligence (AI), fused with big data, will potentially solve many key clinical trial challenges.

By Open Medscience

Open Medscience is a platform to discuss a range of imaging modalities including radiology, ultrasound, computed tomography, MRI, nuclear medicine (PET & SPECT) and radiation therapy.