Postgraduate Medicine

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Pediatric Aspects of Nuclear Medicine S. Treves To cite this article: S. Treves (1975) Pediatric Aspects of Nuclear Medicine, Postgraduate Medicine, 57:3, 125-132, DOI: 10.1080/00325481.1975.11713991 To link to this article:

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Pediatric Aspects ol Nuclear Medicine Pediatric application of the principles and techniques of nuclear medicine has unique features.1 Although children are exposed to the same diseases as adults, they often react differently to the same aggressor agent. Thus, in nuclear medicine the results of studies in adults cannot be directly extrapolated to children. In pediatric applications, special techniques are necessary and studies must often be tailored to the individual patient. The pediatric population ranges from premature infants to young adults. While there are some distinct physiologic differences between the adolescent and the adult, these differences are marked between the premature, newborn, or young infant and the adult. Some of these differences are reflected in the biologic handling of radiopharmaceuticals in these age groups. For example, the blood disappearance rates of internally administered radiopharmaceuticals may be faster or slower in children than in adults, and the fraction of administered radiopharmaceutical taken up by an organ may be higher in children. Washout rates of radioactive gases used for lung studies are faster in children. In addition, little is known about the normal handling of radiopharmaceuticals in infants in the first weeks of life. During the last few years, the number, variety, and complexity of nuclear medical examinations that can be performed in children have increased impressively. Two major factors ap-

Vol. 57 • No. 3 • March 1975 • POSTGRADUATE MEDICINE

The development of new radiopharmaceuticals and the availability of the gamma scintillation camera and computerized analysis have made possible pediatric application of nuclear medical techniques in a number of body systems. Pediatric applications require special techniques and individually tailored studies.

S. TREVES, MD Harvard Medical School Boston

pear to be partly responsible for this growth. 1. Recent accomplishments in radiopharmaceutical development. The application of technetium 99m to clinical use is one of these advances. This radionuclide is easily available from a 99 Mo~ 99 mTc generator system. It has a physical half-life of six hours and decays with the emission of a 140-kev monoenergetic gamma ray that can be detected with almost 100% efficiency by the gamma scintillation camera. Radioactive technetium can be administered in millicurie amounts, yet it results in a relatively



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••mrc sodium pertechnetate

Cerebrospinal fluid



"mTc sodium pertechnetate


"mTc microspheres of HSA "mTc macroaggregates of HSA u•xe in saline or as gas

Heart and great vessels

"mTc sodium pertechnetate "mTc HSA


"mTc sulfur colloid u•1 rose bengal


"mTc sulfur colloid "mTc denatured red blood cells


"mTc-Fe-ascorbic-acid-DTPA complex "mTc-Sn-DTPA complex "mTc sodium pertechnetate u•1 orthoiodohippurate


"mTc diphosphonate

Bone marrow

"mTc sulfur colloid

Tc, technetium; DTPA, diethylenetriaminepentaacetic acid; In, indium; HSA, human serum albumin; Xe, xenon; I, iodine; Fe, iron; Sn, stannum.

low dose of absorbed radiation. In general, the radiation dose incurred by patients undergoing nuclear medical procedures is comparable with and often lower than that received during specialized roentgenographic procedures. Various 99 "'Tc-labeled radiopharmaceuticals have been developed to study a large variety of organs. Other radionuclides, such as indium 111 and, hopefully, iodine 123, are also becoming more generally available for clinical use, thus expanding further the variety of examinations possible. Table 1 lists some radiopharmaceuticals commonly used in pediatric nuclear medicine. The reduction in radiation exposure with these radiopharmaceuticals has helped to expand


the scope of nuclear medical examinations in children to include not only the study or evaluation of suspected malignant disease but also the evaluation of nonmalignant disease and organ function. 2. The availability of gamma scintillation cameras and computer systems for acquisition, storage, and analysis of data. With the introduction of gamma cameras of the Anger design, it has become possible to obtain anatomic and functional information simultaneously. These cameras now have spatial resolution capabilities of 3 or 4 mm, and magnifying collimators increase the overall resolution. Patient positioning is easier for the gamma camera than for the rectilinear scanner. These characteristics make the gamma camera the most ideal detection instrument in pediatric nuclear medicine at present. Linking small digital computer systems with the camera allows analysis of the anatomic and quantitative functional information within a clinically useful time. For example, it is possible to evaluate regional lung ventilation and perfusion quantitatively 2 and to detect, localize, and quantify left-to-right shunts by radionuclide angiocardiography.8 These computer systems can provide complex analysis of functional data shortly after completion of the study. Their full diagnostic potential has barely been grasped at the present time. The development of new radiopharmaceuticals and the availability of the gamma camera and computerized analysis have made possible pediatric application of nuclear medical techniques in a number of body systems. Brain and Cerebrospinal Fluid

Three types of nuclear medical investigations can be performed in pediatric patients.4 •5 Cerebral radionuclide angiography (dynamic) requires injection of 99 "'Tc sodium pertechnetate for routine brain scintigraphy and study of the first transit of the indicator through the head with the gamma camera (figure 1). The procedure is used to evaluate changes in the cerebral blood flow, such as those resulting from arteriovenous malformation, major arterial occlusion,

POSTGRADUATE MEDICINE • March 1975 • Vol. 57 • No. 3

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Figure 1. Normal anterior cerebral radionuclide angiogram. First frame shows arterial and beginning of capillary phases, second frame shows capillary and beginning of venous phases, and third frame shows venous phase. Three frames are recorded by gamma camera during first transit of intravenously injected ...'Tc sodium pertechnetate. Note symmetry of circulation over head.

infarct, subdural effusion, subdural hematoma, and cysts, and to evaluate the vascularity of certain tumors. Brain scintigraphy (static) is used to detect intracranial tumor, brain abscess (figure 2), subdural effusion, subdural hematoma, infarct, arteriovenous malformation, cyst, and certain congenital anomalies. Radionuclide cisternography is used to evaluate the regional flow of cerebrospinal fluid in hydrocephalus. In patients with diversionary shunts (ventriculoperitoneal, ventriculoatrial), very small amounts of radionuclide may be introduced into the valve reservoir to evaluate the patency of the shunt and to measure (in milliliters per minute) the flow of cerebrospinal fluid.

Thyroid uptake with radioactive iodine today plays a small role in the study of thyroid disorders in children. RadioimmunoaSsay and competitive protein-binding techniques that allow 'measurement of serum levels of thyroid hormones define thyroid function more easily and objectively. 6 Thyroid scintigraphy depicts the location and morphology of the thyroid gland. The most frequent indications in children are to evaluate neck or thyroid masses and to search for ectopic thyroid tissue. 99 "'Tc sodium pertechnetate has been found to be quite adequate for thyroid scintigraphy in children and has the advantage of a much lower dose of absorbed radiation than that with 131 I (about 1/200 that of 131 I). 7



Thyroid uptake tests serve to evaluate thyroid function. Iodine 131 is used in children, in small amounts (fraction of a microcurie) because of the undesirable beta radiation associated with its decay. Beta radiation only increases the radiation dose and is not readily detectable externally. Longer counting times are then necessary to obtain adequate statistics with these small doses.

Lung scintigraphy with radioactive particles uses 99 "'Tc macroaggregates or microspheres of human serum albumin (HSA). 8 Following intravenous injection, these particles lodge in the capillary bed of the lungs, where they remain for a period sufficient for detection and are then slowly digested and reabsorbed. This technique is used to obtain detailed images of pulmonary

Vol. 57 • No. 3 • March 1975 • POSTGRADUATE MEDICINE


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Heart and Great Vessels

Figure 2. Brain abscess in 15-year-old girl with cyanotic congenital heart disease. Scintigrams reveal well-defined area of increased uptake of radioactive technetium over superior parietal region, which was found to be an abscess and was drained surgically. Location of abscess was defined with aid of radioactive markers. Angiography was not necessary before surgery.

blood flow distribution. Multiple projections can be obtained. Its major use in pediatrics is for detection of pulmonary embolism, an entity that apparently does not occur as frequently in children as in adults. Lung scintigraphy with radioactive gas is used to evaluate regional distribution of pulmonary ventilation and perfusion. Xenon 133 is given by inhalation to study regional ventilation and intravenously in saline to study regional perfusion. Although the physical half-life of 133Xe is 5.1 days, its biologic half-life is short (about 10 seconds in children). More than 95% of the administered dose is eliminated from the lungs in the first two minutes. With the use of a computer, information on regional lung function is available numerically or in the form of quantitative images (figure 3). Classic methods require patient cooperation in performing certain respiratory maneuvers, such as breath holding. Since infants and small children cannot collaborate actively in the performance of controlled respiratory exercises, special simplified methods have heen developed that do not require breathing maneuvers. 2


Radionuclide angiocardiography evaluates the circulation within the heart, great vessels, and lungs by the use of radiopharmaceuticals and the gamma camera. 3 This relatively new method can provide important qualitative (morphologic) and quantitative (functional) information about the cardiovascular system. Some desirable characteristics of radionuclide angiocardiography are its simplicity, relative lack of trauma, insignificant risk, and low radiation dose. The radiopharmaceutical solution injected is of small volume and does not produce hemodynamic disturbance. The use of on-line digital computers is necessary to take full advantage of the information obtained by this technique. The radiopharmaceuticals that are generally used are 99 mTc sodium pertechnetate or 99 mTc HSA. Intravenous injection of the radioactive solution allows visualization of the superior or inferior vena cava, right atrium, right ventricle, pulmonary artery, lungs, left atrium, left ventricle, and aorta. The information can be evaluated visually by the study of serial images or by the visual or numerical study of time-activity curves generated from one or more regions of special interest over the cardiovascular structures. Abnormal patterns of radionuclide flow are associated with various congenital and acquired cardiovascular abnormalities, eg, transposition of the great arteries, tetralogy of Fallot, tricuspid atresia, pulmonary artery stenosis, aortic stenosis, and agenesis of a pulmonary artery. Obstruction, deviation, and congenital abnormalities of the superior or inferior vena cava can be demonstrated within a few seconds with radionuclide angiocardiography. Evaluation of enlargement of the pericardial space (pericardial effusion, tumor) or cardiomegaly (rheumatic myocardium) is also possible. Radionuclide angiocardiography is quite useful to demonstrate patency of palliative shunts, eg, the Potts, Waterston, Blalock-Taussig, and Glenn anastomoses, and to evaluate ·

Pediatric aspects of nuclear medicine.

During the last few years, the number, variety, and complexity of nuclear medical examinations that can be performed in children have increased impres...
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