MSRS 6473 Vascular Noninvasive Imaging Procedures

Transcription

1 MSRS 6473 Vascular Noninvasive Imaging Procedures Rex T. Christensen MHA RT (R) (MR) (CT) (ARRT) CIIP Basic Physics Equipment Cardiac Positioning Perfusion Pathology MRI 1

2 Animal Magnetism MRI Basic Physics 2

3 Hydrogen Atom Has the simplest atomic structure. Contains one proton and one electron. The nucleus of a hydrogen atom contains only a proton. Therefore, hydrogen atoms are often referred as protons Abundant in the body. Water Molecule H 2 O Hydrogen in the body is found predominately in three forms: 1. Free water in body fluids (CSF) 2. Water bound to large molecules (proteins) 3. Hydrogen atoms within fat. 3

4 MR Active Nuclei (Hydrogen) Angular momentum or spin. Posses an electrical charge (+) If two of these characteristics are present it induces the third magnetism Called a magnetic moment Precession Precession is the wobble of a top Precessional Frequency is the speed it wobbles. (Mhz) 4

5 Larmor Frequency: The Larmor frequency is also called the Precessional frequency. Precession is a wobble of the hydrogen atom. Hydrogen Atoms before being placed in the MRI: 5

6 Hydrogen Atoms after being placed in the MRI: Hydrogen and Field Strength As field strength increases the number of Hydrogen atoms becomes more visible. 6

7 Resonance: When an RF pulse is turned on and its frequency matches that of the frequency of the hydrogen atom energy is transferred. This tips the hydrogen atoms down into the transverse plane (90 degrees). Resonance Precessional frequency of hydrogen is MHz/T Precessional frequency of hydrogen: 1.0T = MHz 1.5T = MHz 3.0T = MHz 7

8 T1 Relaxation: T2 Relaxation: 8

9 Longitudinal (T1) and Transverse (T2) Magnetization (relaxation) Relaxation times for different tissues: 9

10 MRI Equipment 10

11 Coils 11

12 Slice selecting gradients. Spatial Localization A combination of these gradients form an oblique slice Axial Sagittal Coronal Imaging Planes 12

13 Magnet Safety As you approach the magnet, the fringe magnetic field gets STRONGER 25 Room Safety MR Safe MR Conditional MR Unsafe 13

14 MRI Safety Bad Day! MRI Safety Ouch! EKG patch burn Pulse Oximeter wire burn 14

15 MRI Cardiac Positioning Two-Chamber View Center parallel to long axis of left ventricle Always center from breathhold (BH) transverse The resultant image will demonstrate the left ventricle, left atrium, left atrial appendage (LAA) and mitral valve (MV) Also called vertical long axis view LA MV LAA LV 15

16 Two-Chamber View Aliased Two-Chamber View The field of view (FOV) that was selected was too small for body habitus; therefore fold over or wrap has degraded this image Wrap 16

17 Four-Chamber View Center parallel to the twochamber view Center in between the papillary muscles on short axis (SA) image The resultant image will demonstrate the right and left atrium, the right and left ventricle, and MV and tricuspid valve Also known as horizontal long axis RA LA TV MV RV LV Four Chamber View 17

18 Malpositioned Four-Chamber View This image was positioned too superior on the twochamber view The resultant image has the aortic valve (AV) in the view making it a fivechamber image Aortic root Malpositioned Four-Chamber View 18

19 Short Axis Center perpendicular to the septum on the four-chamber view The resultant image demonstrates the left and right ventricle in a nice round shape (donuts) RV LV Short Axis with Motion Artifact Impaired image quality because patient had difficulty holding their breath Motion artifact 19

20 Left Ventricular Outflow Tract of Aorta Center perpendicular to the aorta The resultant image demonstrates the left ventricle, AV and outflow tract Also known as coronal view RA LVOT & AV RV LV PA Left Ventricular Outflow Tract of Aorta 20

21 Flow Artifact Turbulent flow in the aorta causing a flow artifact on left ventricular outflow tract (LVOT) image Flow artifact Flow Artifact 21

22 Para-Axial Aorta Center parallel to the AV using the LVOT image The resultant image demonstrates the cusps of the AV Para-Axial Aorta 22

23 Three-Chamber View Center parallel to the long axis of the left ventricle and aorta This image RV demonstrates the AV, AV MV, and right and left ventricle LA MV LV Parasagittal Aorta Center parallel to the ascending and descending aorta The resultant image shows the aorta in a candy cane view Descending aorta RPA Ascending aorta Descending aorta Ascending aorta 23

24 Parasagittal Aorta MRI Challenges Claustrophobia Motion Cardiac Triggering (arrhythmias) Coil selection Pacemakers Gradient strength (faster imaging) Coronary Arteries/Stents 24

25 MRI Perfusion Heart 25

26 Why MRI Perfusion? Resolution < 2mm No radionuclide Visualize subendocardial defects Morphology and of the heart Comparisons Nuclear(including PET) MRI Spatial Resolution cm mm Voxel resolution 3 5 cm 8 10 mm SNR 6 20 CNR 8 >100 Difference in resolution PET, position emission tomography CNR, Contrast to noise ratio SNR, signal to noise ratio 26

27 Magnetic Resonance Imaging Hyperenhancement Images Post Percutaneous Transluminal Coronary Angiography (PTCA) (2D) Post (6 weeks) 41 YO M with 1-mm ST Elevation Myocardinal Infarction 1 Week Ago and Negative Nuclear Scan Yesterday A very thin lateral wall subendocardial infarction below the limits for detection by standard nuclear imaging well visualized by the high spatial resolution afforded by cardiovascular magnetic resonance (CMR). Note, the high CMR resolution to demonstrate the dual supply of the posterior lateral papillary muscle suggested by variable scar (middle arrow). 27

28 MRI Pathology Hypertrophic Cardiomyopathy 28

29 Right Ventricle Perforation: 85 YO Un Life threatening rupture on CMR CT 29

30 Multi Detector CT (MDCT) Pitch Pitch combines the table distance traveled per 360- degree rotation with the slice thickness. Pitch (P) = Distance the table travels per rotation (d)/total collimation (W) 30

31 Protocols Coronary Angiography Factors to Consider Timing of the contrast bolus Number of beats per slice IV Metropolol (beta blocker) lowers heart rate Cardiac Gating Contrast Contraindications 31

32 Cardiac Gating CT Contraindications for Iodine 32

33 Contrast Protocols Iodine Concentration (300 to 400 mg iodine/ml) Volume and Rate of contrast injection (80 ml 140 ml) (3 6 ml per second) Timing of the delivery (bolus tracking HU) Coronary Artery Nomenclature LMCA Left Main Coronary Artery (10 15mm) Bifurcates LAD and CX Trifurcates LAD, CX, and IR LAD Left Anterior Descending. Anterior 2/3 of septum, lateral edge of lt. ventricular wall CX Circumflex Artery. Lateral and Posterior walls of the lt. ventricle IR Intermediate Ramus 33

34 Coronary Artery Nomenclature RCA Right Coronary Artery. Lateral wall of rt. Ventricle AM Acute Marginal Branch PD Posterior Descending Artery PV Posterior Left ventricular Artery DG Diagonal Branch. A branch off one of the main arteries. Normal Coronary Anatomy Aortic or Valsalva Sinus. Located just above the Aortic Valve. RCS Right Coronary Sinus LCS Left Coronary Sinus NCS Non-Coronary Sinus PA Pulmonary Artery 34

35 Aortic Valve Right Coronary Artery Anomalies 35

36 Right Coronary Artery Anomaly RCA originates off the LMCA Left Main Coronary Artery Anomalies 36

37 Left Main Coronary Anomaly Absence of Left Main Coronary Artery LCMA absent in 0.41% of patients Left Main Coronary Anomaly LMCA originates off the Right Coronary Sinus 37

38 LAD Coronary Artery Anomalies Left Circumflex Coronary Artery Anomalies 38

39 Left CX Anomaly CX originating off the RCA Normal LAD 39

40 Normal RCA Myocardial Perfusion Normal Myocardium enhances homogeneously in both rest and stress scans 40

41 Myocardial Perfusion Myocardial Perfusion Defect Ischemia myocardial defect presents at stress, disappears at rest. Necrosis myocardial defect presents at stress and at rest. Myocardial Perfusion Intramural perfusion defect is placed in the inner layers of myocardium Transmural perfusion defect is located in the entire myocardial wall Subendocardial perfusion defect is placed in the subendocardial myocardium. Usually this is not well identified by SPECT studies 41

42 Myocardial Perfusion Myocardial Viability Negative viability the contrast material accumulates in nonviable tissue, showing a typical hyperenhancement Positive viability The density on the hypoattenuated myocardial segment is homogeneous in comparison with normal segments CT Perfusion Normal Stress Rest and Stress 42

43 Cardiac Scoring Cardiac Scoring 43

44 Agatston Score Based on Hounsfield Units (HU) 1 = HU 2 = HU 3 = HU 4 = 400 or greater HU Agatston Score Summaries all the HU s from all of the slices 1 10 = Minimal = Mild = Moderate 400 or more = Severe 44

45 CCTA and IVUS method IVUS miniaturized transducer is introduced during coronary catheterization 45

46 Attributes Cross-platform for Myocardial Infarction Imaging SPECT, single photon emission computed tomography; ECHO, echocardiography; MRI, magnetic resonance imaging Characteristic SPECT ECHO MRI Spatial resolution Sensitivity Specificity Quantitation Speed Cost Cost-effectiveness Platform availability Claustrophobia Proven in MI User-independent Reproducibility Subendocardial imaging Variability Viability References: Westbrook, Catherine and Kaut, Carolyn (1998). MRI In Practice, 3rd ed., Blackwell Science, Inc. Malden, Ma. Biederman, Robert et al. (2008). Cardiovascular MRI Tutorial: Lectures and Learning. Lippincott Williams & Wilkins. Philadelphia, Pa. Haaga, John et al. (2009). CT and MRI of the Whole Body. Mosby Elsevier. Philadelphia, Pa. 46