MUGA (Multigated) study is a procedure in which patients RBCs are radiolabeled, ECG gated and then ECG gated scintigraphy is obtained. Single or multiple studies of the left or right ventricle are done. Alternative names for the study are RNV (Radio Nuclide Ventriculography) and RNA (Radio Nuclide Angiography). 

Data are collected from several hundred cardiac cycles to generate images of the beating heart that is presented as single or composite cardiac cycle.

This study is used to assess the following: 

1. Regional and global wall motions

2. LEFT or RIGHT ventricular ejection fractions

3. Cardiac chamber size and morphology

4. Ventricular systolic and diastolic function  

MUGA may be done in a resting state, during exercise or during pharmacological interventions. Some centers perform a post NTG / sorbitrate MUGA immediately after the exercise MUGA. 

Procedure:

1.     Patient preparation:

REST:

No special preparations are required at rest.  Fasting is preferred. No need to withhold any medications. ECG electrodes must be secured firmly to the skin to ensure optimal ECG tracings. 

EXERCISE:
Patient should be fasting at least for 2-4 hours and hemodynamically & clinically stable. Exercise in the form of supine or upright ergometry is generally preferred. Patients who cannot exercise can undergo a pharmacological stress test with dobutamine. Any medication that may interfere pharmacological stress test should be stopped in consultation with treating physician for 24-48 hours prior to the test.   All emergency resuscitation measures should be available when conducting such a test. A trained physician for any resuscitation must be available in case of emergency. 

INFORMATION PERTINENT TO PERFORMING THE STUDY:

Adequate history should be taken regarding arrhythmias, drugs, cardiac risk factors etc. Evaluation for physical capability should be done. Standard 12 lead ECG should be viewed before the study. 

PRECAUTIONS:

1.  You should know the safe handling of blood products.
2.  When in-vitro labeling is done you should be absolutely certain about administering the blood to the same patient.
3. Patients with unstable heart rhythms or implanted devices should be very closely monitored because heart rate response to exercise is unpredictable in such patients. 

RADIOPHARMACUETICALS:

Administered adult dose is usually 15-30mci 99mTc using in-vivo, invitro or modified in vivo methods.
Child dose: 0.2-0.4mci/ Kg body weight.  Minimum dose 2- 4 mCi
Largest radiation absorbed dose is to the heart.  0.02mSv / Mbq.
Approximately 25% of the administered dose is excreted by urine within 24 hours.
Stannous pyrophosphate is typically used in most centers.
Stannous DTPA may also be used.
Labeling is least consistent with in-vivo method, intermediate with modified in vivo and best in in-vitro method.
Most of centers prefer in vivo labeling as it is simple & there is no risk of handling blood products. 

IMAGE ACQUISITION:

FOR REST STUDY:

A. Instrumentation :

Use LEAP or LEHR collimator.
Check the ECG gating working or not.
Use appropriate RR interval beat acceptance window to account for beat variability and ectopy. 
Systolic function determinations are less susceptible to beat variations than the diastolic functions.
LIST mode acquisition is useful in patients with heterogenous beats & retrograde gating for diastolic parameters. 

1.     Acquisition parameters. 

Conventionally a 64 X 64 matrix is used. A minimum of 16 frames per cycle is required for accurate assessment of cardiac function parameters.  Higher frame rate of 32-64 is required for detailed measurement of diastolic filling parameters and is required for absolute volume measurements. Acceptable diastolic parameters are possible with 16 frames if Fourier curve fitting is employed. 

Image should be acquired so that heart will occupy 50% of useful field of view.  Typically 3-7 million counts should be acquired per view.  Usually 3 views are acquired in supine position.  

1. Anterior view

2. LAO – best septal view

3. Left lateral view.  

FOR STRESS STUDY:

Acquisition parameters same as above except that frame rate may be reduced to 8-16 cycles per cycle. 16 frames per cycle are ideal.  

Bicycle ergo meter is done in supine or semi supine position. Adjust the detector suitably to get best septal view. 2-4 minute images may be acquired at each different workload.  However workload should not be decreased during the exercise.  

Patients who cannot exercise: dobutamine infusion can be done.  

After exercise study is finished one more study should be acquired to assess post exercise recovery. 

SOURCES OF ERROR WHILE DOING MUGA STUDY.

1. RBC labeling: Certain medications and illnesses like renal failure can cause poor RBC labeling and hence reduced target to background ratio. 

Patient positioning: The ejection fraction may be inadequately calculated if the best septal view is not possible.  [i.e. inability to separate left ventricle from other cardiac structures.]

2. Gating errors: Poor ECG signal or complexes in which other than the QRS complexes are dominant will result in spurious gating and data will not be interpretable. Care should be taken to ensure that proper QRS complex is the true gating /triggering signal.  Some times you may have to change the leads in the ECG gating device so as to select the proper QRS complexes.  

3. Heart rate variability: Significant variations in the heart rate during the study will compromise estimations of diastolic filling indices.  

4. Image statistics:  Inadequate count density usually less than 3 million counts may result in poor images and compromise image interpretations  

5. Processing errors:  Inclusion of non-ventricular activity or exclusion of ventricular activity from ventricular ROI may result in under or over estimation of the LVEF. Inclusion of left atrium in ROI will alter the LVEF. Inclusion of aorta or spleen in background ROI will alter the LVEF values.