Nuclear - Diagnostic tests/Procedures/Protocols/Artifacts Flashcards
What is the most sensitive and specific tests for prediction of recovery of regional function after revascularization?
PET - Most sensistive
Echo - Most specific
MRI - varies by technique
What are indications for performing pharmacologic stress testing in lieu of a treadmill test for single photon emission computed tomography myocardial perfusion imaging (SPECT MPI)?
- Severe, symptomatic PAD
- Chronotropic incompetence
- LBBB
- Neurologic and muscular disorders
- Paced-rhythm
What is the problem with LBBB or paced rhythms and exercise nuclear stress testing?
- may develop a septal perfusion abnormality in the absence of septal branch or LAD disease
- due to decreased septal blood flow at rapid heart rates
***pharmacologic stress testing –> HR not increased –> specificity improves
What is an abnormality that may be seen with permanent pacing on SPECT MPI?
- asynchronous contraction of the myocardium
- Perfusion defects in the absence of disease:
- septum
- inferior wall
- apex
What are the agents of choice for pharmacologic stress testing in patients with LBBB and v-paced rhythms?
- Adenosine
- Dipyridamole
- Regadenoson
What is the mechanism of action of adenosine?
Why is this medication used?
- nonselective agonist that causes coronary vasodilation when it activates the A2A receptor
- Least amount of binding to the other receptors (A1, A2B, A3) which produce most of the side effects when activated
- chest pain
- bronchiolar constriction
- mast cell degranulation (flushing)
- negative chronotropic, inotropic, dromotropic effects
What are contraindications to pharmacologic stress testing with adenosine?
- Medications:
- caffeine and aminophylline
- comptetive adenosine receptor antagonist (binds without stimulating) –> prevent vasodilation –> lower sensitivity for detection of CAD
- dipyridamole
- induces vasodilation
- resting study will have a high baseline blood flow –> flow reserve during stress will be decreased
- if used in addition to adenosine or regadenoson –> half-lives are markedly prolonged due to inhibition
- caffeine and aminophylline
- Severe obstructive lung disease (with active wheezing)
- adenosine or dipyridamole –> could stimulate A2B/A3 receptors that produce bronchial constriction
- 2nd / 3rd degree AV block or SSS without a PPM
- A1 receptor activation (located in the SA, AV, atrial and ventricular myocytes) –> negative chronotropic, inotropic, dromotropic effects
How long should these agents be held prior to stress testing?
- Caffeine
- Aminophylline-containing compounds
- Dipyridamole
- Caffeine: 12-24 hours
- Aminophylline: 24-48 hours
- Dipyridamole: 24-48 hours
What is the prognostic value of ischemic EKG changes with normal perfusion images on:
- exercise stress testing
- vasodilator stress testing
- Exercise
- low risk of cadiac death or MI ( < 1% per year, if no DM)
-
Vasodilator
- Varies widely - some with normal coronaries and others with prognostically important CAD
- Angiography recommended to resolve prognostic uncertainty raised by these discordant findings
Describe the findings and next step
- 60 year old male with DM and exertional chest pain
- GXT:
- 3:30 minutes on Bruce protocol
- EKG: 2mm horizontal ST depression
- Symptoms: mild angina at peak
TID (transient ischemic dilation) + LHC
- high risk finding
- important finding if ischemic symptoms present
Describe the findings
MVCAD (multiple high-risk features)
- LAD perfusion defect
- marked TID
- Increased RV uptake of tracer at stress
- high risk finding
Describe the findings
- 64 yo male with prior MI presents with refractory pulmonary edema
- LVEF 28% with wall motion abnormalities
- LHC: chronic subtotal occlusion of large dominant CFx
Revascularization has a high probability of improving global and regional LV function
- Resting PET images (Rubidum-82 and F-18 FDG)
- Rubidium –> perfusion tracer
- FDG –> metabolism tracer
-
Hibernating myocardium
- Lateral wall demonstrates resting perfusion defect with robust metabolism (FDG)
Describe the findings:
- 56 year old female with hyperlipidemia and aypical chest pain
Anterior attenuation artifact (likely breast)
- Improvement in perfrusion from rest –> stress
- most likely attenuation artifact
- SPECT: anterior attenuation artifact, most likely breast
- Angiogram: normal
Describe the findings and next step:
- 54 year old female with intermittent chest pain x 24 hours
- EKG with nonspecific ST-T wave abnormaltiies
- Resting Tc-99m myocardial perfusion scan following injection (during chest pain) is obtained
- Findings: Large territory of inferior and lateral resting ischemia
- Next step: cardiac cath
- Angiography 90% lesion with ruptured plaque in large dominant LCX
Describe the findings and outcomes
- 63 year old male preesents with stable exertional chest pain x 1 year.
- Exercise Tc-99m myocardial perfusion scan:
- Exercise: 9:20 minutes on Bruce
- Symptoms: angina at peak stress c/w presenting symptoms
- ECG: 1.5mm horizontal ST depression at peak stress
- Recovery: ST depression/angina resolve 2 minutes into recovery
Aggressive medical therapy would be similar to PCI in this patient for reduction of cardiac death and myocardial infarction
- COURAGE trial - SIHD
- PCI relieves symptoms over the 1st year but doesn’t improve mortality or outcomes
- SPECT findings:
- inferior perfusion defect suggestive of one vessel CAD
Describe the anatomical orientation
Describe the findings:
- 37 year old male with palpitations and SOB x 3 years, slightly worse over the last few days
- Pharmacologic myocardial perfusion scan is performed
Diaphragmatic attenuation is present, with evidence for a chronic cardio-pulmonary process
- Increased RV uptake at stress and rest
- marked RV hypertrophy and massive RV dilation
- Dx: Ostium Secundum ASD
*** mild inferior wall ischemia
Describe the findings
Describe the findings
What do findings of RV uptake on nuclear mean?
LV becomes ischemic –> RV becomes a greater contributor to the LV
When is SPECT MPI appropriate following STEMI?
Stable patients prior to discharge who are not scheduled to undergo cardiac catheterization
- Class I - LOE B
- MPI (dipyridamole, adenosine, or regadenoson) prior or early after discharge to look for inducible ischemia is indicated since the results can further risk stratify the patient and help the clinician select the most appropriate treatment strategy
What are limitations to SPECT MPI in women?
What is an alternative test that can improve accuracy?
- Small LV chamber size
- Breast attenuation
- Obesity
- PET
- higher diagnostic accuracy
- addressess all problems
What is the problem with chamber size and SPECT MPI in women?
- women have smaller hearts than men –> diminishes accuracy
- adversely affects (especially if thallium-201 used)
- image quality
- diagnostic accuracy
What can be done to improve the diagnostic accuracy of SPECT MPI in women with breast attenuation artifact?
- breast attenuation artifact can be improved (70% –> 90%) with integration of
- rotating projection images
- wall motion
- attenuation correction
When performing reorientation on a myocardial perusion study, it is important the orientation line should be _________ to the long axis of the heart.
Parallel
*
When performing myocardial perfusion image, the most important post acquisition quality control procedure that should be performed is to review this:
Raw projection data
*
What are common sources of artifact:
- Acquisition set-up
- Collimation
- Radius
- Positioning
- # of Projections
What are common sources of artifact:
- Patient related
- Soft tissue attenuation
- Extra-cardiac activity
- Motion
- Irregular R-R interval with Gated SPECT
What are the advantages to gated SPECT imaging and why should it be performed?
- Myocardial function
- wall motion and thickening
- Functional Data for Prognosis
- EF calculation
- Myocardial viability
- Increased Test Specificity (Diagnostic Accuracy)
What is a collimator?
- lead shields with multiple holes used to cause “selective interference” of gamma rays not traveling in a selected direction
- device used to produce a parallel beam of rays or radiation
Give examples of collimators and what studies are performed with these collimators?
- High resolution
- Most Tc-99m perfusion studies
- General All Purpose
- TI-201
- MUGA
- Fan-Beam
- AC on triple-head systems
- no longer in use
Explain differences between Hi-resolution and General Purpose collimators?
- Longer bore
- Smaller hole diameter
- Thicker septa
****All lead to increased resolution and decreased sensitivty
Describe resolution effects on collimation
- Resolution too high
- images become noisy
- leads to decreased clinical specificity
Describe the image
- Comparison of High Resolution to All Purpose collimator
- High Resolution –>
- clearer defect in septal area due to higher counts
What is one situation in which the positioning of the patient would be depdent on the body rather than the heart being in the center of the field of view?
Attenuation Correction acquisition
How do under/over sampling (angular sampling or projections) affect image quality?
- Under-sampling –> loss in resolution
- Over-sampling –> loss in count density
- 64 Projections / FWHM = 7 Pixels
- difference in resolution
- more pronounced defect
- 32 Projections / FWHM = 8.2 Pixels
What is Full Width at Half Maximum (FWHM)?
- important measurement to assess the efficiency of the scintillation couting equipment
- should typically be < 10%
- characteristic of a function or a graph curve and describes how wide the data distribution is
What occurs as a result of large radius?
- Contrast loss
- Resolution loss
- Spatial distortion
****Smaller Radius / closer to patient –> better resolution and image quality
What is the result when reconstruction limits (volume) are improperly selected?
- Partial volume effects
- Difficulties in display scaling
- Truncation
Describe the finding
Mismatched volume
Describe the findings
Truncation
What is the function of filters in SPECT image acquisition and processing?
- Optimize signal to noise ratio in tomographic reconstructions
- Remove inherent reconstruction artifacts
- Provide image enhancement
What are the types of filters in perfusion imaging?
- Ramp
- before applying filter = no filter
- images are usually noisy
- Butterworth
- Hanning
- Hamming
- Metz
- Parzen
What are the results of reorientation artifacts?
- Create or mask lesions
- Geometric distortion of the heart
- Prevent accurate slice matching
Describe the findings
Reorientation artifact
A 56-year-old man with hypertension, hyperlipidemia, and active tobacco use presents to your office in consultation for an abnormal stress test. He has epigastric burning both with eating meals and inconsistently with climbing stairs for the past month. The patient is limited in his ambulation due to plantar fasciitis, therefore a vasodilator myocardial perfusion study was performed. Electrocardiographic and hemodynamic data were unremarkable. Perfusion imaging shown below:
Proceed with coronary angiography
- High-risk features such as severe defects or abnormal LVEF, portend an increased adverse cardiac event rate, including cardiac death
- SDS = 5 (percent ischemic myocardium of 8%)
- SSS (summed stress score) = 22
- considered a severely abnormal defect
A 55-year-old man with hypertension, diabetes mellitus on insulin, stage-III chronic kidney disease, obstructive sleep apnea on CPAP, history of transient ischemic attack, and obesity (body mass index = 34 kg/m2) is being considered for non-urgent femoral popliteal bypass. He is largely sedentary due to multiple orthopedic issues and because of claudication at low levels of exertion. He denies angina or dyspnea. His blood pressure is 160/80 mmHg and heart rate is 78 BPM. His baseline electrocardiogram shows a normal sinus rhythm with non-specific ST and T wave abnormalities.
A regadenoson myocardial perfusion imaging study is performed.
Proceed to surgery
- small area of mild ischemia in the distribution of the LCx, confirmed by quantitative analysis
- defects of this magnitude do not significantly alter the risk of perioperative cardiac complications
*
A 65-year-old woman with diabetes mellitus on insulin (hemoglobin A1c of 8.1%), hypertension, and hyperlipidemia presents to your office with a two-week history of epigastric “burning” when climbing two flights of stairs. Her vital signs are blood pressure of 138/70, heart rate 75, and body mass index of 30 kg/m2. Physical examination is unremarkable. Baseline electrocardiogram is normal. A treadmill exercise stress MPI study is performed. The patient completes 3 minutes of exercise on the Bruce protocol limited by epigastric discomfort and knee pain. She achieves 70% of maximum predicted heart rate with a blunted blood pressure response to exercise. The stress electrocardiogram shows 1 mm of down-sloping ST depression at peak exercise that returns to baseline at two minutes into recovery.
Her myocardial perfusion imaging results are as follows:
Proceed with coronary angiography
- large area of ischemia in a multi-vessel distribution (LAD, LCx)
- TID present
- may be due to extensive subendocardial ischemia, stress-induced LV stunning, LV cavity dilation, or a combination of all of these mechanisms, and is an independent predictor of cardiac events
Describe the process of TID?
- may be due to:
- extensive subendocardial ischemia
- stress-induced LV stunning
- LV cavity dilation
- or a combination of all of these mechanisms
- independent predictor of cardiac events
How can TID be quantified?
TID ratio
- stress LV volume / rest LV volume
- upper limit of normal = 2 SD above the mean
- 1.1 - 1.35 depending on the imaging and stress protocol
You are asked to see a 52-year-old man with diabetes mellitus, hypertension, paroxysmal atrial fibrillation, and obesity for an abnormal stress test. The stress test was ordered for a cardiac ischemia evaluation prior to initiation of flecainide for atrial fibrillation. His vital signs at baseline are: heart rate of 85 and blood pressure 140/72 with a body mass index of 40 kg/m2. The patient completed 6 minutes of exercise on the Bruce protocol, achieving 104% of maximum predicted heart rate. The patient demonstrated a normal hemodynamic response to exercise and reported dyspnea without chest pain. The electrocardiogram portion of the study was negative for ischemia. The myocardial perfusion images were as follows:
Coronary angiogram
- Decline in LVEF between rest and post-exercise stress of 9%
- drop in LVEF ≥ 5% post stress is associated with increased risk of subsequent cardiac events in diabetic patients
- abnormal post-stress LVEF < 50% –> predictor of cardiac death
- SPECT: small area of ischemia involving the distal anterior wall of the LV
What is the significance of post-stress drop in LVEF by gated myocardial perfusion SPECT?
- Drop in LVEF ≥ 5% post stress
- associated with increased risk of subsequent cardiac events in diabetic patients
- may indicate MVCAD
- Post-stress LVEF < 50% –> predictor of cardiac death
- Post stress LVEF 30-50%
- intermediate risk despite having only mild-moderate ischemia on MPI
What tracers can be utilized for myocardial viability testing?
- F-18 fluorodeoxyglycose (FDG) PET imaging
- Thallium-201 with a 4-hour rest/reditribution protocol
- not proven to provide benefit in a sub-study of the STICH trial
What evidence supports the use of FDG PET imaging for myocardial viability testing?
- PARR-2
- F-18-FDG PET imaging-assisted management of patients with severe LV dysfunction and suspected CAD
- Ottawa-Five sub-study
- observed those who underwent FDG PET and adhered to PET results directed recommendations for revascularization –> trend toward better 1 year outcomes
A 66-year-old patient underwent exercise SPECT stress testing for evaluation of chest pain. The patient exercised for 10 minutes on a Bruce protocol and reached target heart rate. The electrocardiogram revealed 1 mm ST segment depressions in the inferolateral leads which began 8 minutes into the exercise period and resolved at 2 minutes into the recovery period. The patient had no chest pain. The perfusion images are shown in the image
< 1% annual CV mortality (if no DM)
- Duke Treadmill Score = 5
- 10 minutes of exercise
- 1mm maximum ST depressions
- no angina
- > 10 METS –> very low prevalence of significant myocardial ischemia
What are causes of RAD (axis between 100-270 degrees)?
- RVH
- LPFB
- MI (Lateral or Posterior wall)
- Vertically positioned heart
- COPD
- PE
- Dextrocardia
- Lead Reversal
- ASD (ostium secundum)
What are signs of severe Hyperkalemia on EKG?
- Tall, peaked, narrow T waves
- Shortened QT interval and ST-T segment depression
- QRS widening and/or bundle branch block
- Bradycardia and sinus arrest
- VT and VF
What are signs of severe hypokalemia on EKG?
- Promenent U waves
- Prolonged QT interval (occassionally)
- ST-T segment depression and flattened T waves
- Various degrees of AV block
- VT/VF
What are causes of U waves on EKG?
What defines a promenent U wave?
- Hypokalemia
- Hypothermia
- LVH
- Drugs (digoxin, quinidine, amiodarone)
- U wave amplitude > 1.5mm
Transmission line-source based attenuation correction utilizes?
Dual energy window simultaneous acquisition
- most commonly accomplished using line sources containing Gadolinium-153
Describe transmission line-source based attenuation correction
- utilizes dual energy window simulatenous acquisition
- utilizes collimated line sources that scan mechanically cross the field of view at each angle and project onto the opposing detector, where an electronic window moves opposite the source to accept transmission photons
Exercise ECG-only stress test
- Based on the Diamon and Forrester pre-test probability of CAD by age, sex, and symptoms, the patient has a low pre-test probability
What is the effect of administration of nitrates (“nitrate-enhanced”) prior to resting injection images in Tc99m SPECT MPI?
improes reader’s ability to detect viable myocardium in severely hypoperfused segments
- similar results with Tl201
- greater ability to predict improvement of regional function after revascularization and to provide important prognostic information
- demonstration of “defect reversibility” on nitrate-enhanced compared to resting images may have better accuracy than either technique alone
Compare sensitivity and specificity for detection of CAD:
- SPECT MPI
- Stress Echo
SPECT has higher sensitivty and lower specificity
Compare sensitivity and specificity for detection of CAD:
- SPECT MPI
- Stress ECG
SPECT has higher sensitivity and specificity
B - 72 yo male with atypical CP, DM, HTN, LVH and able to exercise
- intermediate pre-test probability of CAD and LVH on ECG
What is the problem with failing to achieve 85% of maximal age-predicted heart rate during SPECT imaging?
reducing the size and severity of the perfusion defects
- may not cause enough of an increase in coronary blood flow to create sufficient flow heterogeneity between areas of the myocardium supplied by an artery with a critical stenosis and those with nonstenosed arteries when the radiotracer is injected
- results in a lower sensitivity (as a result of absence / smaller degree of inducible ischemia)
What are clinical endpoints which can prompt injection of the radiotracer at submaximal heart rates?
- typical anginal symptoms
- profound ECG changes of ischemia
What are advantages of Tc99m single-isotope imaging strategy over a dual-isotope strategy?
- flexibility of performing 1-day stress/rest, rest/stress, or 2-day sequence
- existence of validated attenuation correction algorithms for Tc99m but not Tl201
- easier interpretation of artifacts
- lower radiation exposure (25-30 mSv vs. 8-15 mSv)
What are advantages of Tl201 dual-isotope imaging strategy over a Tc99m single-isotope strategy?
improved efficiency in the nuclear cardiology laboratory
- can be completed in shorter time period
- no waiting for liver clearance (as required for Tc99m)
What are the components of the Duke Treadmill score?
- Anginal chest pain
- Magnitude of ST-segment changes
- Exercise time
****chronotropic incompetence not included
What is the strongest prognostic exercise test variable in exercise stress testing?
exercise duration
Describe the Duke Treadmill Score
Exercise capacity (time, Bruce protocol) - 5x magnitude of ST-segment deflection (mm) - 4x angina index (0 = none, 1 = nonlimiting, 2 = limiting)
- Annual mortality
- Low ( >5) - 0.3%
- Intermediate (-10 to +4) - 1.3%
- High ( < -10) - 5%
What are absolute contraindications to exercise stress testing?
- Hypotension
- ACS within 24 hours
- if stable, can be considered
- AS (critical)
- Allergy/sensitivity (to stress agent)
- CAD (severe LM disease)
- LVOTO (severe)
- LV failure (severe)
What are relative contraindications to exercise stress testing?
- Large AAA
- LBBB
- RV pacemaker
Relative to treadmill exercise ECG testing in women, SPECT MPI does which of the following?
Improves the specificity
- does not compromise the sensitivity in detection of CAD
What is the effect of LVH on count statistics?
- it may improve count statistics
- which results in better-quality images with the risk of hiding small areas of ischemia
What are causes of artifact in male patients on SPECT MPI?
- abdominal protuberance (obesity or ascites)
- anterior chest attenuation related to obesity
- elevated diaphragm
- causes inferior wall attenuation
***shifting breast artifact typically not a problem in males
Breast attenuation is likely to create SPECT artifacts resulting in which of the following?
Decreased specificity in the LAD territory
- attenuation –> lower specificty to correctly diagnose CAD in this territory
How often is breast attenuation artifact seen in MPI in women?
40%
Describe how each effects attenuation in SPECT MPI:
- utilizing higher-energy pharmaceutical
- reviewing rotating projection images
- performing quantitative analysis
- using pharmacologic in place of exercise
- utilizing higher-energy pharmaceutical
- use of Tc99m results in less attenuation and scatter –> gives higher quality images than Tl201
- reviewing rotating projection images
- identification of the position of the diaphragm and breasts
- estimation of the movement of the heart in the vertical and horizontal planes
- performing quantitative analysis
- using gender-matched normal files for QA helps to eliminate attenuation artifact
-
using pharmacologic in place of exercise
- does not limit or reduce attenuation artifacts
- higher background usually seen with pharmacologic stress –> poor image quality
What is quantitative analysis used for?
Comparison of a given patient to which of the following normal databases gives the best specificity?
- help differentiate attenuation artifacts from true perfusion defects
-
Gender matched
- normal databases are usually matched for type of protocol, form of stress, and type of agent
- improve specificity most by accounting for differences in the amount of breast attenuation
What are factors that will improve pre-test probability of disease but not help with artifact recognition on SPECT MPI QA?
- Age matched
- Weight matched
- Risk factor matched
What does prone imaging allow for recongition of (and improves accuracy) in SPECT MPI?
diaphgragmatic attenuation
- provides greater separation between the heart and the diaphragm –>
- less inferior wall attenuation in comparison to a supine image
- usually imaged both prone and supine –> comparison made
Compare the spatial and temporal resolution:
- Gated SPECT MPI
- strees Echo
Gated SPECT has lower spatial and temporal resolution
- spatial resolution = 14-16 mm
- temporal resolution = 8-16 time frames / RR interval
- further limited by resulting low counts in each time interval
What is one of the major benefits of gated SPECT MPI?
improves specificity and reader confidence
- gating obtained from all cardiac cycles
- help differentiate perfusion defects due to scar, which do not move or thicken, and attenuation defects that move and thicken
What are maneuvers that can facilitate liver clearance of Tc99m radiotracers and improve image quality?
waiting > 30 minutes before imaging following pharmacologic stress
- both Tc99m sestamibi and tetrofosmin are cleared in a time-dependent manner
- adding exercise to the stress tests can also facilitate clearance –> lower liver and GI counts
What will these maneuvers following Tc99m radiotracers cause?
- drinking carbonated drinks and water
helps to release gas
When is dobutamine the most appropriate stress agent for testing?
active airway disease - or being treated with theophylline
What is the reason dipyridamole, regadenoson, adenosine are effective pharmacologic SPECT stress agents?
increase coronary blood flow 2.4-4.5 times above baseline
- act as direct or indirect vasodilators of the resistance arterioles
Why do obstructed vessels demonstrate perfusion defects with stress imaging?
- arterioles are maximally dilated at baseline
- no significant vasodilation can be induced with these agents
Which adenosine receptor induces coronary vasodilation when activated?
A2A
- A1 –> AV conduction delay or AV block
- A2B and A3 –> bronchospasm by facilitating mast cell degranulation
What are the cardiovascular effects of adenosine?
- Potent vasodilator
- Vagal inhibition at low doses leading to increase in HR
- Bradycardia and AV block at high doses
- Reduced adrenergic activity
What is one contraindication with use of dipyridamole?
hepatic dysfunction
- half life = 30-45 minutes
What is are benefits of Regadenoson over Adenosine in pharmocologic stress testing?
- selective activation of A2A receptors
- rapid onset (30 seconds)
- longer duration of action (2-5 minutes)
- allows for more efficient simplified protocols
Relative to adenosine, patients receiving regadenoson are more likely to have which of the following?
headaches
- ADVANCE MPI 1 and 2 randomized trials
- demonstrated noninferiority for regadenoson relative to adenosine for detection of ischemia
- perfusion defects similar with both groups
- decreased symptoms of dyspnea, flushing, chest pain
Describe coronary steal phenomenon
- phenomenon where an alteration of circulation patterns leads to a reduction in the blood flow directed to the coronary circulation
- happens as a result of narrowed (diseased) coronary arteries being always maximally dilated to compensate for decreased upstream blood supply
- dilating resistance vessels in the coronary circulation –> causes blood to be shunted away from the coronary vessels supplying the ischemic zones
What is one finding that occurs with coronary steal phenomenon in those undergoing vasodilator pharmacologic SPECT and PET stress tests?
ST changes and/or symptoms
- cause coronary steal by dilating vessels with noncritical stenoses that are supplying collaterals to areas with high-grade stenosis
- this may result in an intracoronary steal due to inadequate flow through the collaterals –> endocardial to subepicardial steal
What is the main advantage of low-level, simultaneous exercise during vasodilator SPECT pharmocologic stress testing?
- reduce side effects (of vasodilators)
- facilitate clearance of tracer from liver and gut
- leads to better image quality
****do not need to achieve target heart rate in order to get benefit described above
What causes a greater increase in coronary blood flow?
- Exercise
- Pharmcologic
vasodilators can produce up to a four-fold increase in coronary blood flow in normal coronaries
- vasodilator > exercise
What is the effect of chronic kidney disease (CKD) on:
- pharmacologic SPECT stress testing
- annual death rate
- annual event rate
- normal SPECT scan
- CKD –> 2.7% annual death rate
- no CKD –> 0.8% annual death rate
- SPECT scan with scar + CKD
- 5.7% annual event rate
- SPECT scan with ischemia + CKD
- 11% annual event rate
What is the most appropriate indication for performing SPECT MPI?
Intermediate pretest probability of CAD
In the evaluation of chest pain syndrome:
- When is it appropriate to have SPECT MPI?
- When is it inappropriate?
- When is it uncertain?
aggressive risk factors modificaiton + stress SPECT MPI for risk assessment
- intermediate-risk score and high-risk occupation
- able to exercise but has potentially nondiagnostic baseline ECG
- stress testing with imaging modality is recommended
What is the next step?
- 63 year old female with FH of CAD, prior tobacco abuse, HTN, DM
- normal SPECT MPI study 1.5 years earlier
- Asymptomatic
- participates in walking club with yoga 5 days/wk after work
No stress test is needed now. Continue aggressive risk factor modificaiton
- asymptomatic patient
- normal stress test within 2 years
What patient population is at the highest risk for serious hypotension in patients receiving regadenoson for SPECT MPI?
patients with autonomic dysfunction
What are factors that may lead to serious hypotension in patients undergoing regadenoson SPECT MPI?
- hypovolemia
- autonomic dysfunction
- Pericarditis / Pericardial effusions
- LM CAD
- Stenotic valvular disease (severe)
- Stenotic CvD with cerbrovascular insufficiency
What side effect persists the longest in patients undergoing regadenoson SPECT MPI?
Headache
- can last up to 30 minutes
How often are side effects seen in regadenoson SPECT MPI studies?
What are the most common side effects?
How long do these effects last?
- ≥ 5%
- Side effects:
- HA
- dizziness
- dysgeusia
- flushing
- feeling hot
- chest discomfort / pain / angina
- ST depression
- dyspnea
- nausea
- abdominal discomfort
- < 15 minutes (usually resolve by this time)
In patients who received an initial adenosine study and were then randomized to receive either a repeat adenosine or a regadenoson, what was the interobserver agreement rate between adenosine vs. adenosine and adenosine vs. regadenoson?
60-65%
- interobserver agreement rate was very similar for three independent blinded readers
What is the best next step?
- 79 year old physically active patient presents for regular follow up with
- PMH: HTN, Dyslipidemia
- Meds: ASA, Atorvastatin, HCTZ
- complaints of epigastric and substernal chest pain which last 15-20 minutes in duration with asociated nause and diaphoresis that have occured at rest
Regadenoson MPI without rest imaging
- repeat vasodilator SPECT MPI –> normal perfusion pattern
What exercise related reasons is pharmacologic stress testing preferred over exercise stress testing?
- unable to achieve
- 85% of age-predicted MPHR and
- 5 METS
What form of stress testing is preferred in patients with LBBB or V-paced rhythm?
Why?
- vasodilator (pharmacologic) stress testing
- high rate of false positive findings on exercise and dobutamine stress tests in these patients
- thought to be HR-related –> much milder increase in HR
What abnormality is often seen in patients undergoing exercise stress testing in setting of LBBB or V-paced rhythm?
- abnormal perfusion in the absence of CAD
- septal wall
- anterior wall (less often)
What is the recommendation if a patient developes rate-dependent LBBB during exercise stress testing?
convert to vasodilator stress test
Describe the methodology a nuclear laboratory might employ to identify attenuation artifacts from true perfusion defects in an obese patient?
change in imaging position
- utilize iterative reconstruction techniques but these do not change attenuation artifacts
How does newer technology - CZT crystal cameras (high-speed cameras) adjust for attenuation?
repeat images of patients in different positions
- open gantry design system does not have the capability of emission or transmission attenuation correction
What is the recommended follow up stress-testing interval for patients with:
- stable symptoms
- intermediate-high global CAD risk
- normal prior stress test 6 months ago
> 2 years
What is the risk of cardiac death and non-fatal MI in:
- < 80 year old male
- negative exercise MPI SPECT
< 1% at 1 year
What are the major benefits of stress-first or stress-only imaging?
50% reduction in radiation exposure
provides similar prognostic information
What should be incorporated into stress-first / stress-only imaging protocols in order to avoid unnecessary rest-imaging?
protocols for addressing potential attenuation artifacts
- Attenuation correction
- SPECT-CT
- Prone Imaging
- for diaphragmatic attenuation
- Breast repositioning
- for breast attenuation
What is the defect shown?
What is the best way to correct this?
breast shadow over the anterior myocardium
- relatively greater perfusion in the inferior wall
- and consequently the perfusion images were suspicious for breast attenuation artifact
Breast taping
- perfusion defect in anterolateral wall resolves after taping
What is the most appropriate next step?
perform dipyridamole stress MPI SPECT
- IV dipyridamole may be administered safely and efficaciously in patients taking oral dipryidamole
How long should dipyridamole be held in the setting of adenosine or regadenoson MPI?
Why?
- > 48 hours
- potential to augment hypotensive effect of adenosine/regadenson
- inhibits cellular reuptake
What is the next step recommendation:
- asymptomatic
- CAC < 100
risk factor modification without further testing
What determines the appropriateness of stress testing after CAC scanning in asymptomatic patients?
incidence of abnormal stress tests, directly related to CAC score:
- < 100 = 1.3%
- 100-400 = 11.3%
- > 400 = 35.2%
What are artifacts during CT-based attenuation correction primarily caused by?
Misregistration
- due to sequential acquisition of CT and SPECT/PET imaging, this can be a significant issue resulting in false-positive perfusion studies
- CT acquision should be in free breating or end-expiration
- CT and PET image overlay should be examined before reconstruction
Describe the findings on post-stress perfusion imaging and next step
Ramp Filter Artifact (may represent) -
repeat imaging after allowing for clearance of subdiaphragmatic activity
Describe a ramp filter
- when filtered backprojection is used to reconstruct images with SPECT
- a ramp filter is applied to decrease the spoke-like artifact and blurring associated with simple backprojection
- ramp filter is applied in frequency space using Fourier transfomration
- In essence, the filter amplifies each spatial frequency in proportion to the frequency
- Leads to reduced blurring and restores fine details to the image by improving contrast
- It also decreases counts in the spatial distribution close to intense activity
- Therefore when there is intense extracardiac activity in the subdiaphragmatic space in close proximity to the heart, the ramp filter can result in a perfusion defect in the inferior wall
What trial demonstrated the effectiveness of regadenoson administration during recovery from inadequate exercise?
the EXERRT trial
- non-inferiority of Reg-recovery vs. Reg-rest (1 hour after)
- sub-diaphragmatic activity significantly lower in Reg-recovery group
- Reg-recovery requires careful monitoring
What can be employed to reduce artifactual defects in this patient?
Pharmacologic stress testing with low level exercise
- adjunctive low level exercise with pharmacologic uptake is an effective way to minimize gut uptake seen on resting images
- drinking a few cups of water can clear up the highgut uptake also
Describe the differences between source-based and CT based attenuation correction:
- Low-noise attenuation maps
- Misregistration
- Simultaneous acquisition of attenuation and emission data
- Radiation exposure
-
Low-noise attenuation maps
- CT-based AC provides low-noise attenuation maps
- Misregistration
- common as a result of patient respiratory or cardiac motion
- Simultaneous acquisition of attenuation and emission data
- performed sequentially, not simultaneously
- Radiation exposure
- radiation dose similar between the two ( < 1-2mSv)
What advantages do AC MPI confer vs. non-AC corrected images?
-
Increased ability to perform stress only imaging
- lower radiation exposure
- improves laboratory throughput
- maintain diagnostic image quality
- Improved Specificity and Normalcy rates
When is it appropriate to perform risk stratification with stress testing in asymptomatic patients after revascularization without residual disease?
- PCI = > 2 years
- repeat revascularization ( < 2 years - 0% and < 4 years - 2%)
- CABG = > 5 years
Describe the findings and next step
Misregistration artifact - correct artifact
- classic example of misregsitration with overlap of the myocardial counts over teh left lung resulting in a lateral wall perfusion defect on stress images
What is the most common cause of CT-PET misregistration artifacts?
rispiratory motion
- due to a temporal resolution of < 1 second for CT as opposed to 1 full respiratory cycle for PET
- result in false positive studies in about 40-60% of all studies
What is the best pre-test protocol (meal, loading condition) that will result in the best image quality?
high-fat/protein, low-carbohydrate diet followed by an overnight fast
- in evaluation of sarcoid –> the interest is in shifting myocardial metabolism towards fatty acid to suppress myocardial uptake of FDG –> FDG signal from the heart would indicate active inflammation
- prolonged fast –> shifts metaboism towards free fatty acid metabolism
How can you induce fatty acid metabolism/utilization in the myocardium?
- high fat/protein, low carbohydrate diet followed by overnight fast
- heparin
- some protocols administer 15 minutes piror to FDG administration
- induces lipoprotein lipase –> promote lipolysis –> shift myocardial metabolism to fatty acids (instead of glucose)
What is the best next step in management?
refer for coronary angiogram
- CT findings:
- multiple calcific plaques in all three coronary territories
- LAD - subtotal occlusion of proximal LAD at origin of D1
What are high risk features on coronary CTA?
- spotty calcification
- “napkin ring” sign
- positive vessel remodeling
- low attenuation plaque
What is the best protocol to evaluate ischemia and myocardial viability in this patient considering redo CABG?
- 75 year old with multiple recent hospitalizations for CHF exacerbation
- PMH: CABG x3 (15 years ago), DM2, HTN, CKD, Dyslipidemia
- Echo: LVEF 30% with diffuse hypokinesis and inferior/inferolateral wall akinesis
- LHC: occluded SVG grafts to RCA and CFx. Patent LIMA-LAD with 70% distal LAD disease and collaterals from LAD to RCA and CFx
Tl201 (2.5-4 mCi) at rest and Tc99m (24-36 mCi) at stress, followed by 4 or 24 hours late thallium redistribution acquisition if needed
What are the advantages of “nitroglycerin-enhanced” Tc99m protocol for viability assessment over Tl201 viability protocols?
- rapid assessment of viability (no requirement for 24-hour redistribution images)
- additional information on LV function and regional wall motion
- lower radiation exposure
What is an absolute contraindication of dobutamine stress echo?
Relative contraindications?
- Absolute
- SBP > 200 mmHg or DBP > 110 mmHg
- Relative
- large AAA
- LBBB
- Paced-rhythm
- ventricular pre-excitation
