Peak enhancement of the liver in children using power injection and helical CT.

OBJECTIVE: Our objective was to determine the level and timing of peak hepatic enhancement in children using power injection of contrast media, helical CT, and computer-automated scan technology. SUBJECTS AND METHODS: Forty-nine abdominal CT studies were performed using computer-automated scan technology. Patients were divided into four groups on the basis of body weight and contrast dose (group 1A, < or = 20 kg and 2 ml/kg; group 1B, < or = 20 kg and 3 ml/kg; group 2, 21-40 kg and 2 ml/kg; group 3, > 40 kg and < or = 2 ml/kg). Contrast injection rates were based on body weight (groups 1A and 1B, 1 ml/sec; group 2, 1.5 ml/sec; and group 3, 2 ml/sec). The peak hepatic enhancement level in Hounsfield units and the time to reach peak enhancement were determined for each patient. RESULTS: The mean peak hepatic enhancement and time to peak enhancement after completion of contrast injection were group 1A, 45 H and 11 sec; group 1B, 62 H and 3 sec; group 2, 52 H and 12 sec; and group 3, 45 H and 10 sec. CONCLUSION: The level and timing of peak hepatic enhancement in pediatric patients can be obtained using computer-automated scan technology. These data may then be used to optimize hepatic enhancement when obtaining helical abdominal CT scans of pediatric patients.

Photon-absorbed fractions for cylindrical geometry: a TLD photon-absorbed fraction model.

The purpose of this study is to develop a mathematical model and calculate photon-absorbed fractions in a homogeneous nonradioactive cylinder placed inside off-center and outside a cylindrical homogeneous distribution of activity. In the second case, both the radioactive cylinder and the nonradioactive one are placed in a tissue-equivalent nonradioactive medium. The values of the photon-absorbed fractions are investigated for various geometrical configurations using water as the material filling the cylinders and the medium in between and an isotope commonly used in Nuclear Medicine, 99mTc. The calculations for off-center cylinders allows for modeling inhomogeneous distributions of activity within a tumor by placing several "cold" cylinders of various sizes in a radioactive finite cylinder. This three-dimensional model calculates photon-absorbed fractions for inhomogeneous activity distributions that can be used in quantitative nuclear medicine for self-absorption correction, thus introducing a more realistic correction than the one-dimensional corrections. These calculations are also used to model the response of a cylindrical TLD (thermoluminiscent dosimeter) placed inside a homogeneous radioactive cylinder and outside the homogeneous radioactive cylinder, in an absorbing nonradioactive surrounding medium. The purpose of these calculations is to evaluate the photon-absorbed fraction in the TLD as an instrument of measuring the time-integrated activity of a homogeneous radioactive source versus an inhomogeneous one. The dependence of the TLD-absorbed fraction on the position of the TLD with respect to the radioactive cylinder is investigated.

Photon absorbed fractions for cylindrical geometry: homogeneous nonradioactive cylinder containing a homogeneous cylindrical distribution of activity.

The purpose of this study was to calculate photon absorbed fractions in tissue surrounding a radioactive source where both the source and the surrounding tissue are assumed to have cylindrical geometry. Specifically, we treated two cases: the case of a cylindrical source of homogeneous activity placed in air, and second, the case of a cylindrical source of homogeneous activity placed in a cylindrical nonradioactive absorbing material. In this study we offer an analytical solution to these problems followed by numerical integration. The computer program allowed for very general calculations, e.g., different tissues, different geometrical setups. Tables of absorbed fractions have been developed for commonly used radionuclide energies and tissue-equivalent material. A comparison between our results and the results of other related studies showed the advantages and limitations of this approach.

Spectrum of chest radiographic abnormalities in children with AIDS and Pneumocystis carinii pneumonia.

This report aims to provide a description of the spectrum of radiographic findings in children with AIDS and Pneumocystis carinii pneumonia (PCP). The chest radiographs of all children with perinatally transmitted HIV infection who had PCP were reviewed. Thirty-eight episodes of PCP were noted in 32 children. The age range was 2-17 months. The radiographic findings were characterized as to pattern, severity, presence of pulmonary air cyst, thoracic air leak, thoracic lymphadenopathy, and pleural effusion. The initial distribution of disease was as follows: diffuse (n = 20), patchy (n = 12), focal (n = 4), normal (n = 2). In nearly one-third of children parenchymal abnormalities were mild enough that most normal lung markings were visible. During the course of the illness pneumothorax was noted in eight cases, pulmonary air cyst in five, and pneumomediastinum in one. Pleural effusions were noted in three (5%) cases. Thoracic lymphadenopathy was not observed in any case. The authors concluded that the initial chest radiographic appearance of PCP in children with AIDS is variable. The initial chest radiograph may be normal. The distribution was patchy or focal in nearly one-half of all cases with parenchymal abnormalities. Pulmonary air cysts or thoracic air leaks were noted during the course of the illness in approximately one-third of all cases.

Significance of periportal low-attenuation zones following blunt trauma in children.

The CT scans of 400 consecutive children evaluated with CT following blunt abdominal trauma were evaluated to determine the frequency of periportal low-attenuation zones, assess patterns of associated intraabdominal injury, and examine clinical outcome. Periportal low-attenuation zones were noted in 60 children (15%). The presence of these zones was associated with a significantly higher incidence of intraabdominal injury (60% versus 11%, p = 0.0001). Injuries most frequently associated with zones of periportal low-attenuation included hepatic (n = 23, 38%), and adrenal (n = 14, 23%). Children who had periportal low-attenuation zones tended to be more physiologically unstable as evidenced by a lower Trauma Score (diffuse, 11.9; focal, 13.4) than children without the zones (15.1, p = 0.0001). The presence of these zones was also associated with a significantly higher mortality rate (13% versus 1%, p = 0.0001). Ten children who had periportal low-attenuation zones and no hepatic injury on CT had a normal appearing liver on gross inspection at surgery or autopsy. In conclusion, periportal low-attenuation zones are common in children who have hepatic injury. These zones may be seen in conjunction with non-hepatic visceral injury or in the absence of intraabdominal injury. The presence of zones of periportal low-attenuation is associated with a higher index of physiologic instability, and higher mortality.

Posttraumatic adrenal hemorrhage in children: CT findings in 34 patients.

The medical records and CT scans of 34 children with posttraumatic adrenal hemorrhage were reviewed. Adrenal hemorrhage was unilateral in 32 children; most injuries were on the right side. Bilateral hemorrhage was present in two children. The injured gland was oval in 27 cases and triangular in nine. Gland size ranged from 7 to 45 mm long and 4 to 30 mm wide. All adrenal hemorrhages had decreased attenuation relative to liver and spleen on contrast-enhanced CT. Ipsilateral diaphragmatic crural thickening was a frequent (61%) associated finding. Ipsilateral intraabdominal (61%) and intrathoracic (44%) injuries were often present. Clinical signs of adrenocortical insufficiency were not observed in any child. In summary, posttraumatic adrenal hemorrhage is uncommon in children. The hemorrhage is usually unilateral, right sided, and associated with ipsilateral visceral injury.

Blunt pancreatic trauma in children: CT diagnosis.

The purpose of this study is to determine the efficacy of CT in the diagnosis of pancreatic injury after blunt abdominal trauma in children. Pancreatic injury was diagnosed at surgery, at autopsy, or on the basis of the development of clinical pancreatitis or a pseudocyst on follow-up imaging evaluation in 18 of 1045 consecutive children examined with CT after blunt trauma. Types of pancreatic injury included laceration in 11 children, transection in two, contusion in one, and tumor with hemorrhage in one. Three children had clinical pancreatitis without a pancreatic abnormality noted on CT. The pancreatic injury was prospectively identified on CT in 12 children (67%). The presence of fluid in the lesser sac was a useful marker for injury to the pancreas. This was noted in 13 children with pancreatic injury, whereas it was observed in only six (1%) of 1028 children in the absence of pancreatic injury (sensitivity, 72%; specificity, 99%). Fluid in the anterior pararenal space was less helpful in establishing the diagnosis of pancreatic injury (sensitivity, 44%; specificity, 98%). A pancreatic pseudocyst developed in four of the 11 survivors. Our experience shows that direct signs of pancreatic trauma may be difficult to identify on CT. Recognition of the limitations of CT diagnosis of pancreatic injury is important in helping to reduce errors of interpretation.