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Figure 2. Normal ERNA. Typically, three projections are obtained: anterior (A), best-septal (B) and steep LAO or lateral (C). The left ventricle is seen in all three projections (arrow). When describing wall motion, the same segmental nomenclature is used as that for planar 201Tl or 99mTc-sestamibi studies (AL-anterolateral; Ap-Apex; IS-inferoseptal; PL-posterolateral; IA-inferoapical; Sep-Septum; Ant-Anterior; Inf-Inferior; Post-Posterior). The spleen (arrowhead) is often seen.

Figure 2. Normal ERNA. Typically, three projections are obtained: anterior (A), best-septal (B) and steep LAO or lateral (C). The left ventricle is seen in all three projections (arrow). When describing wall motion, the same segmental nomenclature is used as that for planar 201Tl or 99mTc-sestamibi studies (AL-anterolateral; Ap-Apex; IS-inferoseptal; PL-posterolateral; IA-inferoapical; Sep-Septum; Ant-Anterior; Inf-Inferior; Post-Posterior). The spleen (arrowhead) is often seen.

fied LAO projection, termed the "best septal" view, separates the left ventricle from other structures and is used for determination of the ejection fraction. In our center, the best-septal view is acquired first. The "anterior" view is obtained by rotating the camera head 40┬░ counter-clockwise from the best septal view while the "steep LAO"

Figure 3. Radiochemistry of 99mTc-RBC labeling. 99mTc-pertechnetate diffuses both in and out of the red blood cell. A reducing agent, such as stannous ion, reduces the 99mTc allowing it to label hemoglobin.

projection is obtained by rotating the camera 30┬░ clockwise from the best septal view.

Intravascular Agents

A tracer is needed that remains in the blood pool for sufficient time to allow for acquisition of the gated blood pool images. There are two approaches to achieve this: labeling of the patient's own red blood cells (RBCs) with technetium-99m or administering a technetium-99m labeled macromolecule such as 99mTc-HSA (human serum albumin). The latter technique is not commonly used since the residence time of 99mTc-HSA in the blood pool is less than that for 99mTc-RBCs. While we are not aware of any case in which hepatitis or HIV has been transmitted through the use of 99mTc-HSA, the use of autologous RBC labeling obviates this concern.

There are three methods available for labeling red blood cells:

(a) In Vivo: In this technique 10-20 ^g/kg of stannous (Sn2+) ions is injected. After 20-30 minutes, 99mTc-pertechnetate is administered. This sequence produces hemoglobin labeling with technetium-99m (Fig. 3). Labeling efficiency (ie. RBC/ Whole blood activity x 100%) with this technique ranges from 80-90%.

In Vitro: In this technique, several ml of blood are withdrawn from the patient labeled in a test tube (using Sn2+ and 99mTc-pertechnetate) and then reinjected. Labeling is reliable with typical labeling efficiencies in excess of 95%.

Modified in vivo (or in "vivitro"): In this technique, Sn2+ is injected in the same manner as for the in vivo technique. After 30 minutes, several ml of blood are withdrawn into a syringe containing 99mTc-pertechnetate. Several minutes are allowed for RBC labeling within the syringe after which the labeled RBCs are re-injected. Labeling efficiency is typically in the 90% range.

The in vitro technique provides the most reliable and highest quality labeling. However, the commercial kit used for in vitro labeling (Ultratag®) is not inexpensive. Moreover RBC labeling is performed on the "bench" removed from the patient. If multiple patients are being imaged, it is crucial that procedures are in place to pre-

vent the inadvertent mixing of blood samples. In our laboratory, we use the in vitro technique in patients in whom we have experienced (or anticipate) poor RBC labeling.

Ejection Fraction

The ejection fraction (EF) as the name implies is the percentage of blood in the left (or right) ventricle that is ejected during contraction of the heart. In echocardiography (and contrast ventriculography) the technologist traces the outline of the left ventricle at end-diastole and end-systole. On the assumption that the left ventricle has an ellipsoidal shape, end-diastolic and end-systolic volumes are calculated from which the ejection fraction is determined. If all ventricular walls contract equally this geometric assumption is accurate. It is less reliable if regional wall motion abnormalities are present. In ERNA, the left ventricular ejection fraction is determined without assumptions as to the shape of the heart; rather it is based on the principle that counts in the left ventricle are proportional to volume (Fig. 4). Using the best-septal view, outlines of the left ventricle at ED and ES are manually drawn or generated by an edge detection program (Fig. 5). Counts in the left ventricle can assumed to be proportional to volume. To correct for background activity in front and behind the heart and scatter from adjacent structures, a background region of interest is drawn adjacent to the heart and the EF calculated. Note that no geometric assumptions are made as to the shape of the heart. Normally the left ventricular EF is >50% while the right ventricular EF is >40-45%.

Parametric Images

In addition to analyzing the images in cine-mode for assessment of regional wall motion, it is possible to generate valuable information from parametric images. (A parametric image can be thought of as an image that condenses information from a series of images). Phase and amplitude images are two commonly generated parametric images. The phase image provides information as to the timing of contraction in various portions of the heart and the amplitude image on the degree of contraction

Clinical Applications

Various modalities are available to assess left ventricular function including ERNA, echocardiography, gated myocardial perfusion imaging (see Chapter 3) and contrast venticulography. The relative strengths and weaknesses of these procedures are listed in Table 1. The technique employed to evaluate ventricular function will depend on local expertise, test availability and the clinical scenario. For instance, in a patient with valvular disease, echocardiography can assess valve structure and function as well as ventricular function. On the other hand ERNA has proven to be an accurate and reproducible method of serially following the EF of patients being treated patients with cardiotoxic drugs such as doxorubicin.

Congestive Heart Failure

Congestive heart failure may be due to left ventricular systolic and/or diastolic dysfunction (Fig. 7). Systolic dysfunction is due to impaired contractility or afterload mismatch (increased wall tension due to an increase in intraventricular pressure or

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