There are many reasons why a person would need to investigate their heart and how it functions. It may be that the individual is suspected of suffering from an un-diagnosed cardiac condition, it is time to check on a known cardiac disease or there is a strong family history of cardiac disease/dysfunction. Another important category is on pre-operative patients who are scheduled for general anesthetic but have never had their cardiac function looked at and tested. Unknown cardiac conditions can be fatal once general anesthesia is involved.
Over the last 20 years there have been extraordinary breakthroughs in cardiac medical imaging. These breakthroughs were once seen as competitive between the different imaging modalities. At MMI we see them as complementary; each has strengths and weaknesses which are best served covering each other. Cardiac Nuclear Medicine, Cardiac MRI and Cardiac CT are found at MMI. Experienced clinicians understand the complexity of cases that present clinically and that each modality has its part in discovering the complete patient diagnosis and in the process creating the best outcomes. At MMI we use only research grade equipment and we are actively involved in cardiac research. This means we are constantly reviewing our imaging techniques and adjusting them in light of insights gained from research.
- MIBI Rest/Stress scan: Molecular imaging is still a sensitive and accurate way of imaging cardiac cells and the images give a detailed representation of the cells’ blood perfusion (ability to receive blood and absorb nutrients). There have been major improvements in SPECT/CT scanning technology especially in advanced computerised analyses programmes (Polar map quantification) and the use of CT in the procedure to compensate for the density of the patient’s body tissue. Myocardial perfusion depends on the state of the cardiac vessels supplying blood. If the vessel is partially or fully occluded the health of the cardiac cells are directly affected. By injecting intravenously a small amount of radiotracer called Tc99m-MIBI we can then scan the cardiac muscle of the left ventricle. Tc99m-MIBI is absorbed through passive transport into myocardial mitochondria in proportion to blood flow. By scanning the patient at rest and then again after physical exercise (or in some cases after a pharmacological agent is introduced to dilate the myocardial vessels) we are able to compare the health of the cardiac cells at rest and after stress. These 2 sets of scans are accompanied with ECG monitoring through both procedures. The cells could be infarcted (death of the cells); they could be ischemic (cells are stable at rest but during exercise, they are not receiving enough blood due to a partial blockage of a cardiac vessel) or they are in good health with plenty of blood supply during rest and exercise. This imaging is directly looking at the effects of blood perfusion to the cardiac cells and gives good indication on how these cardiac cells will react to restricted blood flow with the ability to compare them to ECG monitoring. Both rest and stress SPECT/CT imaging data sets are gated and also give an ejection fraction for the left ventricle. The scans are compared by fine slicing the cardiac image and by quantification using advanced cardiac programs.
- Cardiac Amyloid (PYP) scan: There is a rise in the number of cardiac patients experiencing heart failure form amyloidosis and this is due in part to an aging population. There are different types of amyloidosis that involve different types of protein chains (ATTRwt chain or AL chain). Additionally, symptoms of amyloidosis are virtually the same to many other types of cardiac conditions. Molecular imaging offers a safe and accurate way of diagnosing this condition. By injecting a radio-pharmaceutical agent known as Tc99m-PYP we are able to diagnose ATTRwt (V1221) protein infiltrated cardiac amyloidosis. Tc99m-PYP seems to differentiate between the different types of protein chains. The imaging involves several planar images that are used to quantify the amount of Tc99m-PYP absorbed into the myocardium. A gated SPECT/CT scan is then acquired to obtain fine slice images all the way through the myocardium and to obtain an ejection fraction.
- PET Cardiac Scanning: PET cardiac scanning is a valuable tool and underutilised in Australia to diagnose the extent of cardiac viability in patients experiencing cardiac failure. It uses glucose metabolism as the mechanism for F1-FDG absorption. Patients are first asked to undergo a resting gated Tc99m-MIBI scan and then to return a 2 days later for the PET cardiac scan. The PET scan is also gated and is displayed for comparison with the resting Tc99m-MIBI scan; both generate ejection fractions and are analysed using advanced cardiac programs including Polar-Bulls-Eye quantification.
Cardiac MRI: Using the power of large 3-Tesla magnets we are able to scan the heart as it beats; dynamic cardiac MRI scanning is a breakthrough in imaging technology. Cardiac MRI (CMR) is a non-invasive imaging technique that does not utilize ionizing radiation. CMR began to be utilizes in the clinical setting in the 1980s and is often considered a “one stop shop” imaging modality of the heart. MMI is involved in active CMRI research and has developed advanced cardiac imaging techniques with a highly specialized technical and reporting team. High definition anatomical images generated by advanced MRI cameras are integral to cardiac research and now available for clinical use. An indication for CMR includes:
- Congenital heart disease
- Valvular disease
- Cardiac tumour
- Pericardial disease
- Assessment of myocardial viability/ventricular function
- Assessment of myocardial perfusion
- Aortic disease
Cardiac CT: Coronary Angiogram or Computed tomography of the heart or Cardiac CT is routinely performed to gain knowledge about cardiac or coronary anatomy, to detect or diagnose coronary artery disease (CAD), to evaluate patency of coronary artery bypass grafts or implanted coronary stents or to evaluate volumetry and cardiac function (including ejection fraction). Cardiac CT is also used for pre-operative planning in cases such as AF Ablation, TAVI, AVR, MVR, as well as general health checks prior to non-cardiac related surgery (such as hip or knee replacements). Advanced processing programs enable each vessel to mapped and analysed for stenosis, plaque and calcium.
MMI recently acquired a new generation GE Revolution CT Smart Cardiac scanner. It can scan at amazing high speed using less radiation and diminishing the chance of movement blurring from the patient. The inventive and intuitive technology assists in quickly setting up complex cardiac procedures reliably and repeatedly. MMI is one of the busiest cardiac CT centres in Sydney giving our staff tremendous experience and abilities.
With Revolution high speed CT, you can capture the whole heart in a single beat, in high definition, with motion-free coronary images at any heart rate. One-beat acquisition for calcium scoring, coronary imaging or comprehensive cardiac assessment can be achieved with or without beta blockers. Advanced processing programs enable each vessel to mapped and analysed for stenosis, plaque and calcium.
Smart Cardiac Technologies include:
- Flexible scan modes to enable rapid and precise TAVR/TAVI planning, delivering low radiation and contrast dose.
- One-beat Auto Gating to intelligently identify the ideal time within the heart cycle to scan the whole heart in a single beat at any heart rate.
- Smart Phase to automatically select the best phase with the least coronary motion.
- The ability to freeze coronary motion even in higher heart rate coronary CT exams.