Case-Based Pitfalls of SPECT and PET: Recognizing and Working with Artifacts

Transcription

1 2:20 PM Friday WORKSHOP V Case-Based Pitfalls of SPECT and PET: Recognizing and Working with Artifacts Sean W. Hayes, MD Associate Clinical Professor of Medicine UCLA School of Medicine Cedars-Sinai Heart Institute Cedars-Sinai Medical Center Los Angeles, CA Perfusion Artifacts 1

2 Motion Artifact Image Pattern: Noncircular cavity Tail Defects 180 deg opposed Noncoronary artery pattern Lateral hot spot Motion Artifact Recognize: Motion on cine images due to patient motion, bouncing heart, or upward creep Solution: Repeat images supine and/or prone Motion correction Make sure patient does not talk or fall asleep during acquisition 2

3 Patient motion Respiratory motion: Bouncing Heart Irregular breathing patterns Sleeping or snoring Talking Technologist telling joke UPWARD CREEP Dual Head detector Single head detector Dectector 2 Dectector

4 UPWARD CREEP Related to imaging too early after stress Associated with decreasing depth of respiration during SPECT acquisition Single detector, inferior wall defect Dual detector, variable defect Extracardiac Hot Spot Hot gut or liver overlapping or adjacent to heart Image pattern: Usually causes artifactual inferior wall defect Solution: Obtain delayed (1 hour later) after eating OR Drink 2 large glasses of water for gut or stomach activity 4

5 Importance of HR at time of Injection Exercise: Achieve 85% MPHR (prognostic data shows a clear change at 80%) Inject isotope at least one minute prior to end of exercise Do not slow treadmill before 1 min after injection CSMC preference: continue exercise 2 additional minutes at one stage lower Be aware of HR at time of injection when interpreting Diaphragmatic attenuation Image pattern: inferior wall defect usually nonreversible but can have reversible component due varying degrees of attenuation Nonreversible defect with normal motion on gated images. Nontransmural inferior MI can also have same pattern Review raw data to look for attenuating structure (stomach, diaphragm) Solution: Attenuation correction Prone imaging 5

6 Extracardiac Attenuation Breast attenuation Image pattern: Defects in anterior or lateral wall usually nonreversible but can be reversible due to shifting breast Solution: Review raw cine data and look for breast size, density and position Do attenuation correction (if available) Do Prone imaging Tape breast and position away from the heart LBBB and Paced Ventricular Rhythm Exercise stress often produces false-positive perfusion defects in the interventricular septum related to HR and prolonged septal systole Vasodilator stress preferred (adeno, regadenoson, dipy) Not exercise or dobutamine Patients referred for pharm. stress frequently entl have significant HR with even minimal exertion Therefore do not use low level treadmill exercise during vasodilator stress in these pts 6

7 Exercise Tl-201 SPECT in LBBB without CAD 84% have LAD territory defects 80% of abnormal segments reversible If apex required to call abnormal then 21% have LAD territory defects (specificity raises from 16% to 79%) Matzer et al JACC 1991;17:1309 Not helped by prone imaging!!! Regadenoson: Selected Populations LBBB and Pacemaker HR increases more with regadenoson than adenosine Thomas, JNM 2010; 51:1730 Advance MPI I and II LBBB (n=64) and Pacemaker (n=93) Regadenoson: no increase in septal or LAD ischemia 7

8 Prone Imaging Can cause artifactual anterior and/or anteroseptal defects, therefore do not do prone imaging only For the inferior wall to be called normal on prone imaging, the inferior wall must have uniform uptake equal to the rest of the LV Gating Artifacts 8

9 Time-Volume and Filling Curves Germano, J Nucl Cardiol 2007;14: Artifacts Gating error Gating errors may cause an artifactually low EF Causes: Arrhythmias causing irregular rhythm (PVCs, a fib) Technical, e.g. gating on T wave Clues: Flashing on raw rotating or gated function images Unusually flat or unusual peaks on time-volume or filling curves 9

10 Artifacts LVH and Small Hearts LVEF = (EDV ESV)/EDV LVH ESV can be overestimated LVEF underestimated Poor tracking of end-systolic contours (see counts inside of end-systolic contours) Small hearts (EDV < 50 ml) ESV can be underestimated LVEF overestimated partial volume effect PET Artifacts 10

11 PET - Misregistration PET images are always attenuation corrected Artifactual defects from misregistration occurs when attenuation and emission scans are misaligned Occurs in 21% of PET scans (JNM. 2004:45; ) Occurs in 40% if CTAC (JNM. 2007;48: ) Causes: breathing, patient motion during PET, or most commonly, patient motion between the attenuation scan and the emission scan. Solutions Software based realign attenuation and emission scans Repeat study PET Scatter Correction Scattered photons can degrade the image quality and introduce artifacts PET images are always attenuation and scatter corrected 11

12 Artifact - Case Examples Patient Motion Respiratory Motion Upward creep Extracardiac hot spot Submaximal heart rate Diaphragmatic attenuation Breast attenuation LBBB Prone artifact Gating artifact irregular rhythm Gating artifact LVH, small hearts No artifact! use optimal imaging technique tailored to patient PET misregistration PET scatter correction Thank you! 12