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Figure 10. List mode acquisition. The rhythm shown in (A) is sinus (beats a, b, c and e) with a single ventricular premature beat (d). The volume curve (B) demonstrates the effect of the premature beat on the ejection frame (EF). Because of a longer diastole and greater ventricular filling following a ventricular premature beat (d), the EF of the next sinus beat (e) is increased. The premature beat itself has a decreased EF while the interrupted sinus beat (c) has a normal EF. With a list mode acquisition, an R-R histogram is generated (C) and only those beats with a normal R-R interval (between the dotted lines) are used to produce the series of ERNA images. As can be appreciated, this is not a perfect solution since sinus beat 'e' (with an elevated EF) will be included while the interrupted sinus beat 'c' (with normal EF) will be excluded from the acquisition.

Figure 10. List mode acquisition. The rhythm shown in (A) is sinus (beats a, b, c and e) with a single ventricular premature beat (d). The volume curve (B) demonstrates the effect of the premature beat on the ejection frame (EF). Because of a longer diastole and greater ventricular filling following a ventricular premature beat (d), the EF of the next sinus beat (e) is increased. The premature beat itself has a decreased EF while the interrupted sinus beat (c) has a normal EF. With a list mode acquisition, an R-R histogram is generated (C) and only those beats with a normal R-R interval (between the dotted lines) are used to produce the series of ERNA images. As can be appreciated, this is not a perfect solution since sinus beat 'e' (with an elevated EF) will be included while the interrupted sinus beat 'c' (with normal EF) will be excluded from the acquisition.

Frequently Asked Questions (FAQ)s

What is meant by a "firstpass study"?

In the body of the Chapter we discussed ERNA in the assessment of left ventricular function. It is also possible to assess left or right ventricular function by injecting a technetium-99m tracer and analyzing the first transit of this tracer through the heart (hence the term first pass study). Since only the first pass portion of the study is

Normal Abnormal

RVEF75% LVEF 67% RVEF 25% LVEF 23%

Figure 11. Normal SPECT ERNA in left panel and abnormal in right panel. The end-diastolic contours are shown in a cage display while the end-systolic contours are represented as solids. The number of voxels at end-diastole and end-systole are determined for both the right and left ventricles and from these the right ventricular ejection frame (RVEF) and left ventricular ejection frame (LVEF) are calculated. Note that this differs from the count-based approach used for planar ERNA studies. (Cases provided by ADAC Laboratories)

analyzed, one is not limited to tracers that remain in the intravascular blood pool (beyond the first pass through the heart). A variety of techniques can be used. These will not be discussed in detail. However, some factors to be considered are:

• In a first pass study, separation of the right ventricle and left ventricle is achieved temporally (Fig. 9). While activity is in the right ventricle, right ventricular function can be assessed; after the activity leaves the right ventricle and reaches the left ventricle, left ventricular function is assessed.

• An anterior or RAO projection is usually chosen to allow separation of right atrium from right ventricle and left atrium from left ventricle,

• The study can be gated in the same way as an ERNA. Non-gated techniques are also available.

• After injection, the bolus of activity spreads. This can be tolerated for assessment of right ventricular function but is a more severe problem with the assessment of left ventricular function. To maintain a tight bolus, a jugular injection is often required.

Does irregularity of the cardiac rhythm cause difficulties in interpreting an ERNA?

The ERNA technique generates a composite cardiac cycle based on several hundred heart beats. The data is then used to generate a time activity curve from which the ejection fraction is determined. Conceptually, one can consider several hundred individual time activity curves superimposed to form the composite time-activity curve. Referring to Figure 10, it can be appreciated that if the data from ventricular premature beats is included, the evaluation of ventricular function during sinus rhythm will be distorted. Cardiac programs allow us to deal with this problem in two ways:

Many programs calculate the average R to R interval and reject data from beats with an R-R interval which are beyond a predetermined acceptance limit (e.g., beats with an R-R interval less than 80% or greater than 120% of the mean R-R interval).

Another approach is to collect the data serially in list mode. This data includes scintigraphic information, timing pulses and R wave pulse information. An R-R histogram is generated and the operator selects the appropriate R-R interval for reformatting the representative cardiac cycle (Fig. 10).

Gated SPECT studies are done for myocardial perfusion imaging. Can gated SPECT ERNA studies be performed as well?

Yes. Gated SPECT myocardial perfusion studies are now routine. The same technique can be applied to ERNA (Fig. 11). Indeed, any camera with the capability of acquiring gated SPECT myocardial perfusion images is also capable of acquiring gated SPECT ERNA. Potential advantages of this technique include: 1) absolute volumes can be calculated in addition to the EF, 2) no corrections is needed for background activity, 3) assessment of wall motion is not limited to those segments seen tangentially on the 3 routine views, 4) three-dimensional phase images can be generated. Once the software to generate volumes, ejection fractions and 3-D phase/ amplitude images is readily available, this technique will probably supplant planar ERNA studies.

Additional Reading

1. DePuey EG, Garcia EV. Updated imaging guidelines for nuclear cardiology procedures, Part 1. J Nucl Cardiol 2001; 8(1):G1-G58.

An expert consensus on how to perform nuclear cardiology studies. Pages G17-29 deal with first pass and ERNA studies.

2. Jain D. Cardiotoxicity of doxorubicin and other anthracycline derivatives. J Nucl Cardiol 2000; 7(1):53-62.

Nicely written article dealing with mechanisms, diagnosis and prevention of cardiotoxicity.

3. Lee K, Pryor DB, Pieper KS et al. Prognostic value of radionuclide angiography in medically treated patients with coronary artery disease: A comparison with clinical and catheterization variables. Circulation 1990; 82:1705-1717.

A valuable report on the extensive experience with exercise ERNA at Duke University in risk stratifying patients with chronic coronary artery disease.

4. Ritchie JL et al. ACC/AHA guidelines for clinical use of cardiac radionuclide imaging. J Am Coll Cardiol 1995; 25:521-547.

Guidelines on the use of nuclear cardiology procedures published by the American College of Cardiology and the American Heart Association

5. Ryan TJ et al. ACC/AHA guidelines for the management of patients with acute myocardial infarction. Circulation 1999; 100:1016-1030.

Guidelines published by the American College of Cardiology and the American Heart Association on the investigation and treatment of patients with an acute MI.

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