Scintigraphy is a technique whereby the transit of a dosage form through its intended site of delivery can be non-invasively imaged in vivo via the judicious introduction of an appropriate short lived gamma emitting radioisotope. The observed transit of the dosage form can then be correlated with the rate and extent of drug absorption. Information such as the site of disintegration or dispersion can also be obtained. Assistance in product development as well as testing of finished products for corporate sponsors are commonly performed.
Procedures
Stress Test: Treadmill
The procedure for nuclear myocardial scanning almost always involves a stress test, stress SPECT, and a resting SPECT (Fig. 7.3). Patient preparation involves fasting for 4 hours prior to imaging. Prior to the stress test, assessment of the patient’s cardiovascular history and physical examination should be performed; baseline vital signs should be evaluated and a 12-lead ECG
performed.
Protocols
Several imaging procedures are available. A common protocol is the same-day single-radiopharmaceutical protocol performed by using 8 mCi (370 MBq) of 99mTc-sestamibi for the stress study. This is followed by the rest study with 24 mCi of 99mTc-sestamibi. SPECT imaging is performed for both studies by using a 180° collection. A 64 X 64 matrix with 32 stops is used.One common approach is to gate the stress study. Because sestamibi or tetrofosmin shows minimal redistribution, the perfusion pattern reflects the myocardial distribution of the tracer at the time of injection (peak stress), whereas function represents the LV function at the time of acquisition. The tracer is injected at rest and gated acquisition is repeated.
Gated SPECT (GSPECT): Principle of ECG Gating
The fundamental principle of ECG gating is illustrated in Fig. 7.4. During a SPECT imaging,camera records multiple projections around the chest along a 180° or 360° arc. Dynamic images are acquired at equal intervals during an ECG-gated acquisition. Acquisition starts with the R-wave on the ECG, which corresponds to the end-diastole. One cardiac cycle, represented by the R–R interval, is divided into multiple frames of equal duration. Image data for each of the frames are acquired repeatedly over many cardiac cycles and stored separately in the computer. During processing, all data of a particular frame are added together to construct a specific phase of the cardiac cycle.
Procedures
Stress Test: Treadmill
The procedure for nuclear myocardial scanning almost always involves a stress test, stress SPECT, and a resting SPECT (Fig. 7.3). Patient preparation involves fasting for 4 hours prior to imaging. Prior to the stress test, assessment of the patient’s cardiovascular history and physical examination should be performed; baseline vital signs should be evaluated and a 12-lead ECG
performed.
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| Protocol for 201Tl |
Image Acquisition and Analysis
Several imaging procedures are available. A common protocol is the same-day single-radiopharmaceutical protocol performed by using 8 mCi (370 MBq) of 99mTc-sestamibi for the stress study. This is followed by the rest study with 24 mCi of 99mTc-sestamibi. SPECT imaging is performed for both studies by using a 180° collection. A 64 X 64 matrix with 32 stops is used.One common approach is to gate the stress study. Because sestamibi or tetrofosmin shows minimal redistribution, the perfusion pattern reflects the myocardial distribution of the tracer at the time of injection (peak stress), whereas function represents the LV function at the time of acquisition. The tracer is injected at rest and gated acquisition is repeated.
Gated SPECT (GSPECT): Principle of ECG Gating
The fundamental principle of ECG gating is illustrated in Fig. 7.4. During a SPECT imaging,camera records multiple projections around the chest along a 180° or 360° arc. Dynamic images are acquired at equal intervals during an ECG-gated acquisition. Acquisition starts with the R-wave on the ECG, which corresponds to the end-diastole. One cardiac cycle, represented by the R–R interval, is divided into multiple frames of equal duration. Image data for each of the frames are acquired repeatedly over many cardiac cycles and stored separately in the computer. During processing, all data of a particular frame are added together to construct a specific phase of the cardiac cycle.
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| Principle of gating |
Principle of gating
Reconstruction of Images
Before reconstruction, it is important to check the raw projection data for potential sources of errors and artifacts. Any error during image acquisition (instruments, patient motion, or soft-tissue attenuation artifacts) is likely to compromise the accuracy of the measurements.
Image Evaluation
The overall quality of the study must be initially assessed by looking for artifacts or other sources of error (patient motion, breast or diaphragmatic attenuation) and to evaluate pulmonary and noncardiac uptake. Reconstructed perfusion images are displayed in a standardized format.On top are the short-axis stress and rest images. The second 2 lines display the vertical long-axis stress/rest images. The final 2 lines contain the horizontal stress/rest images. Images are usually reviewed in both a continuous color format, such as gray scale, and in a color scale.
In addition to viewing the wall motion from a 3-dimensional perspective, wall thickening can be visualized by viewing the gated short, vertical long, and horizontal long axes. Polar maps can be helpful in quantifying abnormalities in perfusion, regional ejection fraction, motion and wall thickening. Also arterial territories are superimposed on the images
Reconstruction of Images
Before reconstruction, it is important to check the raw projection data for potential sources of errors and artifacts. Any error during image acquisition (instruments, patient motion, or soft-tissue attenuation artifacts) is likely to compromise the accuracy of the measurements.
Image Evaluation
The overall quality of the study must be initially assessed by looking for artifacts or other sources of error (patient motion, breast or diaphragmatic attenuation) and to evaluate pulmonary and noncardiac uptake. Reconstructed perfusion images are displayed in a standardized format.On top are the short-axis stress and rest images. The second 2 lines display the vertical long-axis stress/rest images. The final 2 lines contain the horizontal stress/rest images. Images are usually reviewed in both a continuous color format, such as gray scale, and in a color scale.
In addition to viewing the wall motion from a 3-dimensional perspective, wall thickening can be visualized by viewing the gated short, vertical long, and horizontal long axes. Polar maps can be helpful in quantifying abnormalities in perfusion, regional ejection fraction, motion and wall thickening. Also arterial territories are superimposed on the images
 |
| Arterial territories |
Quantitative Measurement and Analysis
LV volumes and LVEF can be obtained easily by applying the software to the reconstructed gated dataset. Software packages developed at Cedars-Sinai Medical Center (QGS), University of Michigan (4D-MSPECT) and Emory University (Emory Cardiac Toolbox) are widely available.LV regional function is more commonly evaluated visually on a cine-loop display. Some programs (e.g., QGS) offer automatic quantitative indices of RWM (in mm) and SWT (per cent diastolic thickness), which are displayed on a segmental, circumferential model of the LV with each segment representing a particular territory of the LV (Fig 7.4). All functional indices should be interpreted in reference to the age-and sex-specific normal database. Normal ranges of the LVEF and regional functional parameters for different programs have been reported.
General Guidelines to Reporting Nuclear Myocardial Scans
The report of technique includes the protocol, the radiopharmaceutical used, and the doses.Results for treadmill stress tests also include the peak heart rate achieved, associated percentage of the maximum predicted heart rate, the duration of the exercise and ECG changes. Comment on ventricular sizes, uptake by the right ventricle, the presence or absence of transient ischaemic dilation and lung uptake should be included. Comment on the size and severity of the defects.
Normal Findings
On perfusion studies result in almost identical stress/rest images with no defects. Tracer distribution is uniform in all the walls of left ventricle.
Fixed Defects
In patients with infarcted myocardium, findings demonstrate fixed defects.
Reversible Defects
Findings in patients with myocardial ischaemia demonstrate reversible defects, i.e., defects on the stress images without a similar defect on the rest images.
Wall Motion Analysis
GSPECT studies can be used to assess regional wall motion and left ventricular ejection fraction when viewed in a cine display. If a perfusion defect is present on stress images and the associated wall is seen to thicken (i.e.: brighten) during systole, one can predict that this represents an area containing viable myocardial tissue. If no thickening is observed, the finding may represent an area of infarction (scar).
Ejection Fraction
LV ejection fraction can be calculated from GSPECT data and provides incremental prognostic information for risk stratification.
LV Dilatation
Left ventricular chamber dilatation may also be noted with pharmacologic stress and is associated with an increased risk for subsequent cardiac event. This represents subendocardial ischaemia or diffuse reduced subendocardial flow reserve.
Pulmonary Activity on Stress Imaging
An increase in tracer uptake in lung on stress imaging is a marker for severe underlying CAD. A lung to heart ratio of greater than 0.33 is suggestive of underlying severe CAD.
LV volumes and LVEF can be obtained easily by applying the software to the reconstructed gated dataset. Software packages developed at Cedars-Sinai Medical Center (QGS), University of Michigan (4D-MSPECT) and Emory University (Emory Cardiac Toolbox) are widely available.LV regional function is more commonly evaluated visually on a cine-loop display. Some programs (e.g., QGS) offer automatic quantitative indices of RWM (in mm) and SWT (per cent diastolic thickness), which are displayed on a segmental, circumferential model of the LV with each segment representing a particular territory of the LV (Fig 7.4). All functional indices should be interpreted in reference to the age-and sex-specific normal database. Normal ranges of the LVEF and regional functional parameters for different programs have been reported.
General Guidelines to Reporting Nuclear Myocardial Scans
The report of technique includes the protocol, the radiopharmaceutical used, and the doses.Results for treadmill stress tests also include the peak heart rate achieved, associated percentage of the maximum predicted heart rate, the duration of the exercise and ECG changes. Comment on ventricular sizes, uptake by the right ventricle, the presence or absence of transient ischaemic dilation and lung uptake should be included. Comment on the size and severity of the defects.
Normal Findings
On perfusion studies result in almost identical stress/rest images with no defects. Tracer distribution is uniform in all the walls of left ventricle.
Fixed Defects
In patients with infarcted myocardium, findings demonstrate fixed defects.
Reversible Defects
Findings in patients with myocardial ischaemia demonstrate reversible defects, i.e., defects on the stress images without a similar defect on the rest images.
Wall Motion Analysis
GSPECT studies can be used to assess regional wall motion and left ventricular ejection fraction when viewed in a cine display. If a perfusion defect is present on stress images and the associated wall is seen to thicken (i.e.: brighten) during systole, one can predict that this represents an area containing viable myocardial tissue. If no thickening is observed, the finding may represent an area of infarction (scar).
Ejection Fraction
LV ejection fraction can be calculated from GSPECT data and provides incremental prognostic information for risk stratification.
LV Dilatation
Left ventricular chamber dilatation may also be noted with pharmacologic stress and is associated with an increased risk for subsequent cardiac event. This represents subendocardial ischaemia or diffuse reduced subendocardial flow reserve.
Pulmonary Activity on Stress Imaging
An increase in tracer uptake in lung on stress imaging is a marker for severe underlying CAD. A lung to heart ratio of greater than 0.33 is suggestive of underlying severe CAD.
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