NMT Boards – Cardiac & Stress Testing

Other names for a gated blood pool study

MUGA, RVG, RNV, ERNA

Main use of MUGA today

Serial LVEF monitoring during cardiotoxic chemotherapy

Cardiotoxic chemo drugs monitored with MUGA

Anthracyclines (doxorubicin) and trastuzumab (Herceptin)

Why MUGA instead of echo for chemo monitoring?

More reproducible EF (low inter-observer variability)

MUGA radiopharmaceutical and dose

Tc-99m RBCs, 15–30 mCi IV

RBC labeling chemistry

Stannous ion reduces Tc-99m from +7 to +4 so it binds hemoglobin beta chain

RBC labeling: lowest and most variable efficiency

In vivo

RBC labeling: highest and most consistent efficiency

In vitro (UltraTag)

UltraTag step that removes extracellular stannous

Sodium hypochlorite oxidation

Free pertechnetate on MUGA appears in…

Thyroid, stomach, salivary glands, bladder

MUGA frames per cycle for systolic function

Minimum 16; preferred 24–32

MUGA frames per cycle for diastolic function

32–64

MUGA energy window

140 keV ±10%

MUGA total counts

3–7 million total; 200,000–400,000 per frame

Standard MUGA views

Anterior, best-septal LAO (~45°), left lateral

What triggers gated acquisition?

R wave on the ECG

Effect of arrhythmia on MUGA

Degrades gating; beat rejection underestimates EF

Acquisition mode recommended with arrhythmia

List mode

Count-based EF formula

(EDC − ESC) ÷ (EDC − background)

EDC 42,000, ESC 18,000, background 4,000 — LVEF?

63%

Normal LVEF

≥ 50%

Background ROI too close to the LV (over spleen/aorta) effect

Falsely raises EF

Background ROI outside the body effect

Falsely lowers EF

Where is the MUGA background ROI placed?

Lateral to the LV at end-systole

LVEF >50% during chemo

Periodic monitoring — continue

LVEF 30–50% during chemo

More frequent monitoring

LVEF <30% during chemo

Contraindication to continuing cardiotoxic therapy

Stroke volume definition

Volume ejected per contraction (EDV − ESV)

Cardiac output formula

Stroke volume × heart rate

Phase analysis shows…

WHEN each LV region contracts (timing/dyssynchrony)

Amplitude analysis shows…

HOW MUCH each region contracts (strength)

Regurgitation index

LV stroke counts ÷ RV stroke counts (near 1 = normal)

Time per frame formula

(60,000 ÷ HR) ÷ frames per cycle

Stress MUGA exercise equipment

Supine/semi-upright bicycle ergometer (not treadmill)

Normal stress MUGA response

LVEF rises ≥5 percentage points; ESV decreases

Abnormal stress MUGA response

EF flat or falls; new wall-motion abnormality

Pharmacologic agent for a stress blood-pool study

Dobutamine (not vasodilators)

Tl-201 mechanism

Potassium analog — Na+/K+-ATPase active transport

Does Tl-201 redistribute?

Yes — significantly, over 3–4 h

Tc-99m sestamibi/tetrofosmin mechanism

Passive diffusion + mitochondrial trapping (membrane potential)

Do Tc-99m perfusion agents redistribute?

No — fixed; need separate rest and stress injections

1-day Tc-99m MPI order

Rest first (8–12 mCi), then stress ~3× higher (24–36 mCi)

Why must rest come before stress in a 1-day protocol?

Residual rest activity would mask reversible stress defects

2-day Tc-99m MPI dose

25–30 mCi each day

Dual-isotope MPI

Rest Tl-201 (~3–4 mCi) + stress Tc-99m agent

Dual-isotope MPI drawback

Higher total radiation dose

Tl-201 MPI dose

2–4 mCi (reinjection ~1.5 mCi)

Tl-201 stress imaging time

About 10 min post-stress

Tl-201 redistribution imaging time

3–4 hours

Tc-99m MPI imaging time after stress

15–60 min

Tc-99m MPI imaging time after rest injection

60–90 min

Why give a fatty meal or water before Tc-99m MPI imaging?

Clear hepatobiliary activity near the inferior wall

Tl-201 physical half-life

About 73 hours

Breastfeeding interruption after Tl-201

2 weeks

Reversible perfusion defect means…

Ischemia

Fixed perfusion defect means…

Scar/infarct (or attenuation)

Breast attenuation affects which wall?

Anterior

Diaphragmatic attenuation affects which wall?

Inferior

Prone imaging advantage

Reduces inferior-wall diaphragmatic attenuation

Prone imaging disadvantage

Can create anterior/septal (sternal) attenuation

CTAC misregistration signature

False ↑ inferior wall + false ↓ anteroseptal/apex

Fix for CTAC misregistration

Re-register CT to SPECT so LV borders align

Standard cardiac SPECT orbit

180° (45° RAO to 45° LPO)

Cardiac SPECT matrix and pixel size

64 × 64; 6.4 ± 0.2 mm

Common low-pass filter for cardiac SPECT

Butterworth

Reconstruction required for attenuation correction

Iterative reconstruction

8-frame vs 16-frame gated SPECT

8-frame underestimates LVEF by ~3 points; 16 preferred if counts allow

Three standard cardiac reorientation planes

Short axis, vertical long axis, horizontal long axis

Short axis slices look like…

Donuts/rings from apex to base

Vertical long axis shows…

Anterior and inferior walls

Horizontal long axis shows…

Septal and lateral walls

LAD supplies…

Anterior wall, anteroseptum, apex

LCX supplies…

Lateral wall (± posterior)

RCA supplies…

Inferior wall, RV (± posterior in right-dominant)

AHA segment model

17 segments

What is TID?

LV cavity larger on stress than rest images

TID ratio abnormal above about…

1.2

TID suggests…

Severe multivessel / left main CAD

Increased lung uptake on stress Tl-201 indicates…

LV dysfunction / severe CAD (lung:heart >~0.5)

Other high-risk MPI signs

Transient RV visualization, post-stress EF drop, multiple reversible defects

"Balanced ischemia" problem in SPECT

Equal 3-vessel disease can look normal (relative imaging)

Rb-82 half-life

75 seconds

Rb-82 source

Sr-82/Rb-82 generator

Rb-82 dose

20–40 mCi per image set (3D ~20, 2D ~40)

Rb-82 extraction fraction

About 65% (rolls off at high flow)

N-13 ammonia half-life

About 10 minutes

N-13 ammonia source and dose

Cyclotron; 10–20 mCi

N-13 ammonia extraction fraction

About 80%

Rb-82 generator daily QC

Sr-82/Sr-85 breakthrough

Coronary flow reserve formula

Stress MBF ÷ rest MBF

Abnormal coronary flow reserve

< 2.0

Rest MBF 1.0, stress MBF 1.8 — CFR?

1.8 (abnormal)

PET advantage over SPECT for perfusion

Absolute blood flow quantification (catches balanced disease)

Flyrcado radiopharmaceutical

F-18 flurpiridaz (FDA 2024)

Flyrcado mechanism

Binds mitochondrial complex I

Flyrcado advantage

F-18 half-life allows shipping and treadmill exercise stress

Cardiac sarcoid FDG prep

High-fat, very-low-carb diet day before + prolonged fast (± heparin)

Cardiac sarcoid diet numbers

35 g fat, <3 g carbohydrate meals

Diffuse myocardial FDG uptake on sarcoid scan means…

Failed suppression (not disease)

Sarcoid: perfusion defect + focal FDG uptake

Active inflammation (mismatch)