Dr. Marcus Chen, Prof. Mickaël Ohana, Dr. Fuminari Tatsugami

Cardiovascular disease is the leading cause of death worldwide¹. Early diagnosis of cardiovascular disease is important for improved life expectancy and effective treatment planning. Cardiac CT Angiography (CCTA) is a non-invasive test to diagnose coronary artery disease (CAD). A multi-center international study has shown that cardiac CTA accurately identifies the presence and severity of obstructive coronary artery disease and subsequent revascularization in symptomatic patients².

Recently both the US and European guidelines for the diagnosis of patients with chest pain have been updated. In the European guidelines cardiac CTA is recommended to exclude acute coronary syndrome in patients with low to intermediate likelihood of CAD³.

CAD-RADS categories

Score	Stenosis	Interpretation	Further investigation
0	0%	Absence of CAD	None
1	1-24%	Minimal non-obstructive CAD	None
2	25-49%	Mild non-obstructive CAD	None
3	50-69%	Moderate stenosis	Consider functional assessment
4A	70-99% single or 2-vessel	Severe stenosis	Consider ICA or functional assessment
4B	Left main >50% or 3-vessel >70%		ICA
5	100%	Total coronary occlusion	Consider ICA and viability assessment
CadRadsN	Non-diagnostic study	Obstructive CAD cannot be excluded	Additional evaluation needed

In the US guidelines cardiac CTA is recommended as a frontline test for the evaluation of patients with stable and acute chest pain who have no history of CAD⁴. In both guidelines cardiac CTA has a Class 1 Level A designation which is the strongest recommendation indicating high quality evidence from clinical trials that CTA is beneficial, useful and safe^3,4.

The Coronary Artery Disease Reporting and Data System (CAD-RADS) provides a standardized reporting framework for coronary CT angiography and was updated in 2022. The classification system provides an assessment of stenosis and plaque burden and a guide to possible next steps in patient management⁵ (Figure 1).

Precise IQ Engine (PIQE) is a Super Resolution Deep Learning Reconstruction* that brings together extraordinary spatial resolution and reduced noise, within a single-rotation scan for confident diagnosis of small coronary vessels, plaques, stents and fine cardiac structures.

The PIQE Deep Learning Reconstruction algorithm is trained using Ultra-High Resolution data with twice the resolution of conventional CT acquired on the commercially available Aquilion Precision CT system, which features UHR 0.25 mm detectors in routine clinical practice. Datasets reconstructed with PIQE empower the clinician with twice the high contrast signal definition, as well as reduced noise, in all three dimensions, relative to conventional hybrid iterative reconstruction. These benefits maintain low contrast detectability, without additional radiation dose to the patient⁶.

The extraordinary spatial resolution of PIQE images reconstructed with 1024 matrix is also beneficial in other cardiac applications including Transaortic Valve replacement (TAVR) planning and follow up examinations where the valve leaflets are seen in excellent detail. In cases with mechanical valves, PIQE provides superior detail of the valve compared to other reconstructions.

PIQE 1024 Matrix training principles
The PIQE reconstruction algorithm features a next generation, three-dimensional neural network trained to identify and preserve signal features, both in-plane and longitudinally, throughout the cardiac volume dataset. Trained on high quality cardiac cases acquired on clinically operating Aquilion Precision systems, PIQE optimizes spatial resolution for clinically relevant tasks and realistic field-of-views. PIQE’s three-dimensional learning also helps ensure continuity of small, longitudinally running vessels, which are often obscured by conventional reconstruction algorithms⁶.

The training cases are acquired with the Aquilion Precision’s Super High Resolution (SHR) mode that yields 0.15 mm anatomical detail. The SHR data is reconstructed with AiCE DLR which implicitly contains all the advanced models of MBIR. In addition to UHR mode, the Aquilion Precision also has Normal Resolution (NR) mode that combines detector channels to generate conventional resolution images in-plane and 0.5 mm nominal slice width equivalent to Aquilion ONE / PRISM Edition and Aquilion ONE / INSIGHT Edition. Raw data acquired in UHR mode can be reconstructed through a down-sampling algorithm to yield simulated Normal Resolution images, that have been demonstrated to be equivalent to true Normal Resolution images¹.

With this approach, both UHR and NR images can be produced from a single acquisition. As a result, pairs of UHR and simulated NR images have perfect spatial alignment, ideal for training a neural network. Simulated NR images are input to the neutral network and the corresponding UHR images are used as the gold standard target images. The neural network learns to maximize the inherent resolution possible with NR images and even enhance resolution further, while decreasing noise⁶ (Figure 2).

The neural network behind PIQE does not learn features solely in the axial plane but rather in three dimensions, meaning signal features are identified and preserved in all three planes. This makes PIQE well-suited for cardiac exams, which are usually reviewed in MPR and curved planes⁶.

PIQE reconstructions are available in both 512 and 1024 matrix, with 1024 matrix providing superior resolution with no loss of reconstruction speed.

The authors were all involved in the initial evaluation and optimization of PIQE 1024 in close collaboration with the engineers at Canon Medical and they have shared a selection of cases that highlight the clinical benefits of PIQE 1024 in cardiac CT.

Dr. Chen, National Institutes of Health, USA

Patient History
This 60-year-old man with BMI 31.3 was asymptomatic. A cardiac CTA was requested for screening for coronary artery disease.

Results

In the LAD, non-calcified plaque is seen concentrically around the vessel with significant positive remodeling resulting in minimal luminal narrowing. The plaque has an overall length of approximately 27 mm. The mid LAD has a calcified plaque causing mild (25-49%) stenosis followed by a second predominately non-calcified plaque region with positive remodeling resulting in minimal (<25%) luminal narrowing.

Clinical Benefit
The positive remodeling is an important plaque feature for the identification of vulnerable plaque. In this case, PIQE 1024 is a reliable technique to assess the extent of the positive remodeling.

Acquisition
Scan Parameters:    One beat volume scan, exposure window 70-80%, 120 kV, ^SURE Exposure
CTDI vol:                     14.5 mGy
DLP:                             173.8 mGy·cm
Effective Dose:        2.43 mSv

Dr. Tatsugami, Hiroshima University, Japan

Patient History
This 73-year-old woman presented with a history of myocardial infarction and a heart rate of 59 bpm. This patient had a chest lead V2-6 negative T wave appearance. The Calcium Score scan showed severe coronary artery calcification with an Agatston score of 954. A cardiac CTA was requested to evaluate the coronary arteries.

Results

With the normal resolution DLR and PIQE 512 images, this stenosis was graded as moderate with a CAD-RADs 3 score (50- 69% stenosis). The visualization of the contours of the non-calcified plaque and the residual lumen were clearly improved with the PIQE 1024 image. In addition, the calcified component of this mixed plaque has sharper boundaries and better delineation in the PIQE 1024 cross-sectional images compared to other reconstructions. This stenosis grading was reduced in the PIQE 1024 reconstruction to a mild stenosis with a CAD-RADs 2 score (25-49% stenosis).

Clinical Benefit
In this case, the increased resolution of PIQE 1024 improves the accuracy of CAD-RADs scorings.

Acquisition
Scan Parameters:    Full beat volume scan, 120 kV, ^SURE Exposure
CTDI vol:                     12.2 mGy
DLP:                             195.5 mGy·cm
Effective Dose:        2.7 mSv

Prof. Ohana, Strasbourg University Hospital, France

Patient History
This 82-year-old patient with a prior diagnosis of COVID-19 underwent a chest CT scan which demonstrated severe coronary calcifications. The patient was referred to the cardiologist who requested a calcium score and a coronary CTA scan due to non-specific ECG changes. The patient's heart rate was 70 bpm at the time of scan.

Results

The calcium score scan showed extensive coronary artery disease (CAD) with an Agatston score of 2118. In the CCTA scan, the Left Main coronary artery (LM) and the proximal and mid-segments of the Left Anterior Descending artery (LAD) show significant wall calcifications with 25-49% stenosis in all these segments.

Clinical Benefit
PIQE 1024 provides better depiction of the vessel lumen which is sharper and less noisy compared to other reconstructions. In this patient, the increased spatial resolution resulted in less blooming artifacts, allowing a more confident assessment of the lumen patency even in the presence of circumferential calcified plaques.

Acquisition
Scan Parameters:    One beat volume scan, exposure window 30-80%, 100 kV, ^SURE Exposure
CTDI vol:                     11.1 mGy
DLP:                             177.2 mGy·cm
Effective Dose:        2.48 mSv

Prof. Ohana, Strasbourg University Hospital , France

Patient History
This 64-year-old man with a heart rate of 51 bpm and a history of cardiac disease, smoking, family history and an ascending aortic aneurysm, underwent screening for ischemic heart disease. A cardiac CTA was requested to evaluate coronary arteries and for the assessment of the ascending aortic aneurysm. The aortic valve was also evaluated.

Results

The clear delineation and sharpness of the aortic valve leaflets with PIQE 1024 outperforms the hybrid IR reconstruction. The opening and closing of the aortic valve leaflets can be clearly confirmed with the PIQE 1024 multiphase images. This tricuspid aortic valve shows calcification on the left cusp but without severe aortic stenosis.

Clinical Benefit
With its high spatial resolution, PIQE 1024 provides excellent delineation of the aortic valve leaflets. This can help to improve diagnostic accuracy for the aortic valve evaluation, which can be very beneficial in the planning of transcatheter aortic valve replacement (TAVR).

Acquisition
Scan Parameters:    Full beat volume scan, 100 kV, ^SUREExposure
CTDI vol:                     22 mGy
DLP:                             351.7 mGy·cm
Effective Dose:        4.9 mSv

Conclusion
PIQE brings excellent spatial resolution and reduced noise within a single rotation cardiac scan while maintaining low contrast detectability and with no additional radiation dose to the patient. PIQE enables more accurate CADRADs scoring, improved visualization of non-calcified plaque, reduced blooming artifact from calcium and stents, improved evaluation of stent patency, excellent valve leaflet definition and accurate TAVR planning.

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