Multiple Gated Acquisition (MUGA) Scanning

What is the primary purpose of a MUGA scan?

Quantify ventricular ejection fractions

Which RBC labeling method provides the highest efficiency?

In vitro

What is the best imaging view for measuring LVEF in planar MUGA?

LAO 45°

What is the normal difference between stress and rest LVEF?

Stress EF should be 5–10% higher

Which factor contributes most to inaccurate EF measurement?

Improper ROI placement

The R-wave on the ECG is used to:

Trigger each frame of acquisition

The R–R interval is divided into equal time segments called:

Frames

What happens if the ECG gating signal is poor?

The cardiac cycle frames misalign, causing motion artifacts

Which acquisition mode is used in most MUGA studies?

Frame mode

What is the typical number of frames per cardiac cycle in a MUGA scan?

16 or 32

The best projection for assessing RVEF is:

RAO 30°

The Time–Activity Curve is used to determine:

Ventricular ejection fraction

During a first-pass study, tracer should be injected:

As a rapid bolus

What is the typical dose range for 99mTc-labeled RBCs in a rest MUGA?

20–30 mCi

Which gating acceptance window is recommended for arrhythmia filtering?

90%

The method with the lowest RBC labeling efficiency is:

In vivo

MUGA scans are commonly used to monitor patients receiving:

Chemotherapy (e.g., doxorubicin)

The most reproducible quantitative measurement provided by MUGA is:

Left ventricular ejection fraction

Compared to echocardiography, MUGA scans are:

More accurate and reproducible for EF

Which of the following can cause false low ejection fraction readings?

Motion artifacts

What is the normal LVEF range for adults?

>50%

What is the purpose of acquiring both rest and stress MUGA scans?

To assess LV performance and CAD severity

What is the main disadvantage of planar MUGA compared to SPECT?

Limited 2D information

A stress LVEF that decreases instead of increasing may indicate:

Ischemic left ventricular dysfunction

Which imaging plane best visualizes the septum for EF calculation?

LAO 45°

Poor labeling efficiency may result in:

Increased stomach, thyroid, or salivary gland uptake

What is the average acquisition time for a rest equilibrium MUGA?

5–10 minutes

The advantage of SPECT MUGA over planar MUGA is:

3D quantitative data

Which of the following is not a direct limitation of MUGA scans?

Geometric assumptions

The correct equation for calculating Ejection Fraction is:

(EDV – ESV) / EDV

Why does equilibrium imaging divide the cardiac cycle into many segments?

To create smoother motion and better temporal detail

In equilibrium imaging, increasing counts per segment improves:

Statistical reliability of the curve and EF measurement

The ROI for LVEF must be drawn at end-diastole because:

It gives the cleanest boundary for LV cavity volume

If background is placed too close to the lung, your EF will appear:

Lower

A very noisy time-activity curve most likely results from:

Inadequate counts per segment

What would artificially elevate an LVEF calculation?

Underestimating background (ROI too “cold”) so max-bg becomes smaller → EF rises artificially

In EF calculation, the minimum counts frame corresponds to:

End-systole

If counts never reach a stable plateau during imaging, it suggests

Poor labeling or infiltration of tracer into tissues outside bloodstream

First-pass imaging relies heavily on:

High temporal resolution during rapid bolus transit

If the bolus is not compact in first-pass imaging, the main problem is:

Smearing of time–activity curves making EF unreliable

Why is max-counts always taken from the end-diastolic frame?

LV cavity is largest, giving highest counts before contraction removes blood volume

Why is the EF formula normalized to background?

To subtract out electronic noise and soft tissue scatter so counts reflect true LV blood pool activity

If end-systole is mis-identified one frame early, EF will:

Increase (because min-counts would be higher if chosen too early)

n first-pass imaging, the best view for RV evaluation is:

RAO orientation to separate RA → RV → PA filling sequence clearly

What makes first-pass imaging fundamentally different from equilibrium imaging?

It captures tracer during a single circulation through the heart

The ideal projection for RVEF in a first-pass study is:

30° RAO

Why is a compact bolus essential for first-pass imaging?

To keep the peaks and valleys of ventricular filling distinct in the time-activity curve

The main advantage of list mode in first-pass imaging is:

Captures all events for flexible rebinning later (best temporal detail)

In rest equilibrium imaging, why are anterior and left lateral views obtained?

To evaluate LV size and shape qualitatively from different angles

What is the purpose of using 42–45° LAO in rest equilibrium imaging?

To best separate LV from RV along the septum for EF measurement

Which injection method yields the lowest labeling efficiency?

In vivo (~75%)

Why does stress MUGA allow up to 120% R-R variance?

Heart rate becomes more variable during exercise, so the window must be widened to keep counts high enough

Stress LVEF is most useful for identifying:

Ischemia-related reductions in systolic performance under workload

When performing stress equilibrium imaging, the patient is most commonly:

Using a supine bicycle ergometer

Why is planar imaging still considered the gold standard for EF?

It has decades of validation with highly reproducible results from a standardized single projection angle

SPECT ventriculography improves assessment of:

RV ejection fraction and multi-view wall motion visualization

Why does rest equilibrium imaging require 2–6 million counts?

To smooth out the cine frames and derive accurate time–activity curves across all cycles

A widened arrhythmia acceptance window does what to the dataset?

Allows more irregular beats into the gated average during stress imaging to maintain count statistics

If equilibrium RBC labeling efficiency is low, what happens?

Blood pool contrast decreases, reducing image quality and statistical confidence in EF measurement

What does the rest equilibrium study primarily measure that first-pass does not?

Wall motion at multiple frames per beat across MANY cardiac cycles (steady-state imaging)

Why does stress imaging use fewer required counts (0.5–1.5 million)?

Lower counts still give adequate information when EF is the main metric during stress, and patients cannot exercise long enough for 6 million counts

What does a failure of EF to rise during stress indicate?

Possible ischemia or impaired contractile reserve

Why is planar MUGA strictly 2D?

It acquires data from only one fixed projection angle, not multiple rotational angles like SPECT

Why do many cardiologists prefer NOT to order MUGA scans?

Requires radiation + blood handling + time + higher cost

Which of the following is a DIRECT limitation of MUGA?

Requires blood manipulation outside the body

What makes MUGA results user-dependent?

ROI placement and labeling efficiency technique variations

Which imaging method is the FASTEST for evaluating cardiac function?

Echocardiography

What major advantage does echocardiography have over MUGA?

No radiation + no IV injection required

Echocardiography struggles in which situation?

Obese patients — acoustic window loss reduces accuracy

Echocardiography is LESS accurate than MUGA because:

It requires geometric assumptions that may not match abnormal hearts

Which cardiac structures are often difficult to see on echo due to positioning?

Back of the heart / posterior structures

Which modality is MOST reproducible for LVEF?

MUGA (Planar)

A major advantage of CMR (Cardiac MRI) is:

No geometric assumptions + highly reproducible EF and wall motion data

Why is CMR not a first-line cardiac function test?

Expensive + limited availability + requires specialized staff/equipment

How long does a typical CMR take?

20 min

What appears WHITE in a spin-echo CMR sequence?

Blood

What appears BLACK in the alternate spin-echo sequence?

Blood

What is the main indication for Cardiac CT?

High radiation exposure + expensive + not first-line for EF measurements

Why is Cardiac CT NOT used as a first-line test for cardiac function?

Involves radiation and is expensive; EF accuracy inferior to echo/MUGA/CMR

Which modality provides the MOST accurate 3D visualization of heart structure and function?

CMR

Which modality requires no radiation AND no IV injection?

Echocardiography

What is the major reason MUGA competes with other modalities?

It provides superior quantitative LVEF measurement (gold standard

Why must nuclear medicine departments remain “dynamic” according to the conclusion slide?

To adapt to echo, CMR, and SPECT competition with evidence-based improvements and better pricing/service

Why is MUGA less convenient than echo?

Must handle blood samples + longer acquisition times + radiation exposure

What unique problem occurs with echo that MUGA avoids?

Geometric assumptions that distort EF in abnormal hearts

Which modality is LEAST available in community hospitals?

CMR

Which modality is highlighted as needing “specific equipment + highly trained readers + not a good starting test”?

CMR