Assessment of Left Ventricular Myocardial Diseases with Cardiac Computed Tomography

Rapid advances in cardiac computed tomography (CT) have enabled the characterization of left ventricular (LV) myocardial diseases based on LV anatomical morphology, function, density, and enhancement pattern. Global LV function and regional wall motion can be evaluated using multi-phasic cine CT images. CT myocardial perfusion imaging facilitates the identification of hemodynamically significant coronary artery disease. CT delayed-enhancement imaging is used to detect myocardial scar in myocardial infarction and to measure the extracellular volume fraction in non-ischemic cardiomyopathy. Multi-energy cardiac CT allows the mapping of iodine distribution in the myocardium. This review summarizes the current techniques of cardiac CT for LV myocardial assessment, highlights the key findings in various myocardial diseases, and presents future applications to complement echocardiography and cardiovascular magnetic resonance.ope

A Non-Rigid Registration Method for Analyzing Myocardial Wall Motion for Cardiac CT Images

Cardiac resynchronization therapy (CRT) has a high percentage of non-responders. Successfully locating the optimal location for CRT lead placement on a priori images can increase efficiency in procedural preparation and execution and could potentially increase the rate of CRT responders. Registration has been used in the past to assess the motion of medical images. Specifically, one method of non-rigid registration has been utilized to assess the motion of left ventricular MR cardiac images. As CT imaging is often performed as part of resynchronization treatment planning and is a fast and accessible means of imaging, extending this registration method to assessing left ventricular motion of CT images could provide another means of reproducible contractility assessment. This thesis investigates the use of non-rigid registration to evaluate the myocardium motion in multi-phase multi-slice computed tomography (MSCT) cardiac imaging for the evaluation of mechanical contraction of the left ventricle

Advanced imaging techniques for cardiovascular research

According to the World Health Organization, cardiovascular diseases (CVDs) are the first cause of death globally. CVDs are a cluster of disorders that involve heart and blood vessels. Among them, coronary artery disease (CAD) is the most important disease in terms of mortality, causing more than 50% of the annual deaths. Over the last decades, many recognized international organisms, such as the World Health Organization and the American College of Cardiology have done great efforts to reduce the mortality and morbidity of CAD. In this line, accurate diagnosis and cost-effective management of CAD have revealed to be of utmost importance. Several imaging techniques are currently used in the clinical practice to provide a diagnosis and clinical assessment of the disease. Among them, Positron Emission Tomography (PET) is considered to be the “gold standard” for non invasive assessment of myocardial perfusion and viability, the two most relevant physiological parameters used to diagnose and manage patients with known or suspected CAD..

Clinical quantitative cardiac imaging for the assessment of myocardial ischaemia

Cardiac imaging has a pivotal role in the prevention, diagnosis and treatment of ischaemic heart disease. SPECT is most commonly used for clinical myocardial perfusion imaging, whereas PET is the clinical reference standard for the quantification of myocardial perfusion. MRI does not involve exposure to ionizing radiation, similar to echocardiography, which can be performed at the bedside. CT perfusion imaging is not frequently used but CT offers coronary angiography data, and invasive catheter-based methods can measure coronary flow and pressure. Technical improvements to the quantification of pathophysiological parameters of myocardial ischaemia can be achieved. Clinical consensus recommendations on the appropriateness of each technique were derived following a European quantitative cardiac imaging meeting and using a real-time Delphi process. SPECT using new detectors allows the quantification of myocardial blood flow and is now also suited to patients with a high BMI. PET is well suited to patients with multivessel disease to confirm or exclude balanced ischaemia. MRI allows the evaluation of patients with complex disease who would benefit from imaging of function and fibrosis in addition to perfusion. Echocardiography remains the preferred technique for assessing ischaemia in bedside situations, whereas CT has the greatest value for combined quantification of stenosis and characterization of atherosclerosis in relation to myocardial ischaemia. In patients with a high probability of needing invasive treatment, invasive coronary flow and pressure measurement is well suited to guide treatment decisions. In this Consensus Statement, we summarize the strengths and weaknesses as well as the future technological potential of each imaging modality

Advanced Imaging Techniques for Cardiovascular Research

Objectives: In this thesis we addressed some of those difficulties by exploring new applications of a 68Galabeled radiotracer (68Ga-DOTA). 68Ga can be obtained from a 68Ge/68Ga generator and has a half-life of 68 minutes, which makes it a convenient candidate for its widespread clinical use. We proposed and validated the use of 68Ga-DOTA as a radiotracer for assessment of myocardial blood flow (MBF), myocardial viability and pulmonary blood flow (PBF). Additionally, we introduced a new methodology to perform a PET scan in which this tracer could be coinjected simultaneously with some other radiotracers such as 18FDG (multi-tracer PET). Lastly, we developed an automatic detector able to perform blood spectroscopy analysis, which offered the possibility to perform multi-tracer PET with minimal human intervention. Methods To test the capability of 68Ga-DOTA to measure MBF, viability and PBF, different groups of Large White pigs underwent PET/CT scans using 68Ga-DOTA as the injected radiotracer. For PBF studies, a group of healthy pigs (n = 4) were scanned under rest conditions. For MBF studies, a group of 8 pigs were scanned under rest and pharmacologically-induced stress in order to perform rest/stress tests, as it is done for humans in clinical routine. Additionally, a group of 5 pigs were scanned 7 days after the induction of a myocardial infarction (MI) to assess viability and MBF in a MI model. MBF, extracellular volume fraction (ECV, for viability assessment) and PBF maps were obtained after fitting the dynamic PET images to the corresponding pharmacokinetic model followed by 68Ga-DOTA in each tissue under study. Global and regional perfusion maps for the myocardial tissue (MBF) and lungs (PBF) were obtained. For validation purposes, the “goldstandard” technique used in tissue perfusion quantification (fluorescent-labeled microspheres (MS)) was simultaneosly performed along with the PET/CT scans. The blood sampling spectroscopic methodology was evaluated and calibrated in vitro using different 68Ga/18F mixtures. Then, it was tested in pigs (n = 3) injected with 68Ga-DOTA and 18FDG in the same acquisition. The activity concentration of each radiotracer in myocardial tissue was subsequently measured ex vivo. The automatic blood sampling detector was built from scratch and characterized using a catheter filled with different 68Ga/18F mixtures. Finally, it was additionally evaluated in vivo in n = 3 pigs under conditions resembling to those encountered in clinical routine. Results Regarding MBF quantification and validation with 68Ga-DOTA-PET, a strong correlation (r = 0.91) between MBF measured with PET and MS was obtained (slope = 0.96 ± 0.10, y-intercept = 0.11 ± 0.19 ml·min−1·g−1). For the myocardial infarction model, MBF values obtained with 68Ga-DOTA-PET in the infarcted area (LAD, left anterior descendant) were significantly reduced in comparison to remote ones LCX (left circumflex artery, p < 0.0001) and RCA (right coronary artery, p < 0.0001). In addition, 68Ga-DOTA-PET detected a significant ECV increase in the infarcted area (p < 0.0001). The correlation evaluation between 68Ga-DOTA-PET and MS as a PBF radiotracer also showed a good and significant correlation (r = 0.74, p < 0.0001). The gamma spectroscopic analysis on blood samples proposed for multi-tracer PET imaging was also succesfully validated, showing a correlation of r = 0.95 (p < 0.0001) for 18FDG concentration in myocardium measured with multi-tracer PET and by ex vivo validation. The blood sampling detector was able to measure the arterial input function in pigs in an experimental setup under realistic conditions. Discussion and conclusions 68Ga-DOTA-PET allowed accurate non-invasive assessment of MBF and ECV in pigs with myocardial infarction and under rest-stress conditions. This technique could provide wide access to quantitative measurement of both MBF and ECV with PET imaging. 68Ga-DOTA-PET was also demonstrated to be a potential inexpensive method for measuring PBF in clinical settings. As for multi-tracer PET imaging, the proposed methodology allowed explicit measurement of separate arterial input functions, offering very similar results to those obtained as a reference from the ex vivo analysis of the tissue under evaluation. Finally, a novel blood sampling device was developed and characterized, showing performance parameters similar to other devices in the literature. Noteworthy, this detector has the additional and unique feature of allowing us to perform multi-tracer PET by means of a gamma spectroscopic analysis of the blood flowing between its detection blocks. All the results summarized in this abstract may contribute to spread the use of PET in clinical routine, either by the clinical use of 68Ga-DOTA as an inexpensive but accurate radiotracer for MBF, PBF or viability assessment, or by the implementation of multi-tracer PET, which could lead to cost reduction of PET examinations by shortening the scanning time and eliminating misalignment inaccuracies. This multi-tracer PET methodology could also be safely implemented using our proposed automated device that permits to perform the gamma spectroscopic analysis on blood samples with minimal human intervention