Imaging
Figure 1: Tc-99m Tetrofosmin Single-photon-emission Computed Tomography Myocardial Perfusion Imaging
dipyridamole are coronary vasodilators, whereas dobutamine is a beta-agonist that increases heart rate and myocardial contractility, with similar effects to physiological exercise. Vasodilators with adenosine and dipyridamole account for 44% of stress perfusion studies performed annually in the US.36
However, both adenosine and
dipyridamole can have minor and major side effects due to non-selective stimulation of all four subtypes of adenosine receptor:
A1 leads to renal vasoconstriction and atrioventricular (AV) nodal conduction block, A2A leads to sympathetic surge and coronary vasodilation and A2B and A3 lead to bronchoconstriction.37
The
selective A2A receptor agonist regadenoson has been demonstrated to rapidly increase coronary blood flow, yet selectively does not cause
AV nodal block and bronchospasm.38,39 Regadenoson has also been
shown to have a better side-effect profile, to be safely administered and to be sensitive in the detection of myocardial ischaemia regardless of age, gender, body habitus or diabetes.40,41
Currently, regadenoson is commercially available and used in many nuclear
cardiology laboratories. Binodenoson, another A2A receptor agonist, has been shown to have similar extent and severity of reversible perfusion defects on SPECT imaging, with fewer side effects.42
One
other agent within the same class, apadenoson, is in phase III trials and may become available in the near future.
A: Stress (top) and rest (bottom). Shown in paired rows. Images were obtained with the cadmium zinc telluride (CZT) detector and iterative reconstruction, shown in the short axis (apex to base from upper left to mid-right), vertical long axis (septum on the left) and horizontal long axis (inferior on the left). These images were obtained in six minutes at rest and four minutes with stress. A mild septal ischaemia is demonstrated.
New Hardware
Dedicated hardware camera systems have been introduced to optimise acquisition geometry and tomographic sampling. The Cardius XPO camera by Digirad, Inc. uses a two- or three-detector configuration and a CsI (Tl) detector to create a more compact system than used in conventional cameras.43 38% reduction in acquisition time.44
This has resulted in a reported D-SPECT by Spectrum Dynamics
uses nine collimated and pixelated CZT detector arrays that are placed in 90º geometry to acquire data focusing on a cardiac region of interest. This system is able to achieve an acquisition time as short as two minutes, with higher sensitivity and better energy resolution than conventional SPECT (see Figure 1).45
Combining SPECT and CT suggests that the use of hybrid imaging provides added diagnostic value; however, the clinical impact on treatment strategy and patient outcome remains to be determined in prospective studies.
B: Stress (top) and rest (bottom). These images demonstrate a large severe minimally reversible (predominantly fixed) anterior defect with minimal reversible ischaemia in the septal and anterolateral segments.
device, sodium-activated cesium iodide and thallium-activated cesium iodide CsI(Tl). However, further research is needed to validate these detectors.
Vasodilator Agents
The commonly used pharmacological radionuclide stress perfusion agents are adenosine, dipyridamole and dobutamine. Adenosine and
34
Other Imaging Modalities
Computer-generated valve planes in MPS can be misaligned with the true valve plane, leading to inaccurate analysis of myocardial perfusion. In a retrospective study, Slomka et al. demonstrated improved quantitative MPS analysis by software co-registration of both CT angiography (CTA) and MPS, thus allowing for CTA-guided contour and vascular territory adjustments. This technique results in a success rate of 96% as assessed visually and improved area under the receiver operating characteristic (ROC) curve for detection of CAD.46
Positron-emission Tomography
PET has long been the gold standard of MPI and quantitation. The most commonly used perfusion tracers for PET are nitrogen-13 (N-13), ammonia, rubidium-82 (Rb-82) and oxygen-15 (O-15) water, with Rb-82 being the most common in the US as it is non-cyclotron- generated and is available to most laboratories.47
Compared with
other perfusion imaging techniques, PET offers many advantages, including higher spatial and contrast resolution, improved image quality, accurate attenuation correction, higher diagnostic accuracy and excellent risk stratification.47
A meta-analysis of studies
EUROPEAN CARDIOLOGY
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92