Thoracic CT technique in children.

Computed tomography (CT) is a powerful tool for imaging the different structures of the child's thorax. Pediatric thoracic CT technique should provide images that allow confident diagnosis at the lowest risk to the patient. New data has increased our understanding of the risk of low-dose radiation. Understanding the technical aspects of CT scanning allows the CT scanner to be optimized for the best combination of image quality and radiation dose. Developments in CT scanning, including multidetector scanners and vascular imaging techniques, are changing the way CT scanning is used. The many imaging options available to the thoracic radiologist require a complex set of decisions when establishing CT protocols and when selecting techniques for different clinical indications. This article presents information on radiation risk and provides an overview of the broad range of factors used when performing pediatric thoracic CT.

Surfactant protein deficiency in familial interstitial lung disease.

OBJECTIVE: To determine the contribution of surfactant protein abnormalities to the development of chronic lung injury in a familial form of interstitial lung disease. STUDY DESIGN: An 11-year-old girl, her sister, and their mother who were diagnosed with chronic interstitial lung disease underwent laboratory investigation of surfactant protein expression in bronchoalveolar lavage fluid and lung biopsy specimens. Nineteen patients with idiopathic pulmonary fibrosis and 9 patients who were investigated for pulmonary malignancy but who did not have interstitial lung disease served as control subjects. RESULTS: The 3 family members were found to have absent surfactant protein C (SP-C) and decreased levels of SP-A and SP-B in bronchoalveolar lavage fluid (BALF). Immunostaining for pulmonary surfactant proteins in lung biopsy specimens obtained from both children demonstrated a marked decrease of pro-SP-C in the alveolar epithelial cells but strong staining for pro-SP-B, SP-B, SP-A, and SP-D. No deviations from published surfactant protein B or C coding sequences were identified by DNA sequence analysis. All control subjects had a detectable level of SP-C in the BALF. CONCLUSION: The apparent absence of SP-C and a decrease in the levels of SP-A and SP-B are associated with familial interstitial lung disease.

BaSO4-loaded agarose: a construction material for multimodality imaging phantoms.

RATIONALE AND OBJECTIVES: Phantom studies are an important part of the evaluation of imaging techniques; however, presently available phantom construction materials are not adequate for studies involving both magnetic resonance (MR) imaging and computed tomography (CT). The purpose of this study was to design a phantom construction material useful for multimodality imaging experiments. MATERIALS AND METHODS: Iodinated contrast agent or BaSO4 was added during the formation of agarose gels. Both CT and MR imaging were performed, and T1 and T2 values and CT numbers (in Hounsfield units) were obtained for multiple combinations of contrast material and agarose. Results. The T2 values of agarose gels span the range of those values found in biologic tissues. Phantoms containing iodinated contrast agent were not stable; contrast agent diffused across concentration gradients. BaSO4-loaded agarose phantoms were stable, however, and varying barium concentrations produced phantoms that spanned the range of CT numbers found in biologic tissues. Addition of BaSO4 did not substantially alter T1 or T2 values of agarose gels. Agarose concentration had only a small effect on the CT numbers of BaSO4 suspensions. CONCLUSION: BaSO4-loaded agarose is an effective material for construction of multimodality imaging phantoms. It provides adequate signal intensity for MR imaging and attenuation for CT, with independently variable contrast in both modalities.

Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large Children's Hospital.

Adjustments of the standard helical CT protocols for adults can result in reduced radiation dose when imaging children. It is the radiologist's responsibility to critically evaluate the CT techniques used at their institution. Adjustments to CT protocols should be made to choose the appropriate mA and pitch when imaging children.

High-resolution computed tomography of the chest in children with cystic fibrosis: support for use as an outcome surrogate.

BACKGROUND: Outcome surrogates are indicators that reflect, rather than directly measure, patient benefit. In order to provide useful results, however, outcome surrogates must be carefully chosen and must meet specific criteria. OBJECTIVE: To support development of high-resolution computed tomography (HRCT) as an outcome surrogate in cystic fibrosis (CF) by demonstrating the ability of HRCT to show short-term improvement in the appearance of the lungs in children with CF. MATERIALS AND METHODS: HRCT was performed at admission and after discharge on 8 children during 15 admissions for acute pulmonary exacerbation of CF. Three radiologists scored each study separately, then compared admission and discharge pairs. RESULTS: HRCT scores improved in 13/15 admissions. Mean score decreased from 25 to 22. The decrease was significant (P = 0.014). Comparison of admission and discharge scans showed improvement in peribronchial thickening (P = 0.007), mucous plugging (P = 0.002), and overall appearance (P = 0.025). CONCLUSION: HRCT has the potential to be a useful outcome surrogate in CF. A necessary attribute of an outcome surrogate is that it improves rapidly with effective therapy. Despite widespread belief among radiologists and pulmonologists that HRCT meets this criterion, no previous report has demonstrated this ability in children. These findings support further development of HRCT as an outcome surrogate in children with CF.

Lungs in infants and young children: improved thin-section CT with a noninvasive controlled-ventilation technique--initial experience.

Three sedated young children underwent thin-section computed tomography (CT) of the chest while breathing and during controlled respiratory pauses induced by means of a step increase in positive-pressure ventilation applied via a face mask. Motion-free inspiratory and expiratory thin-section CT images were successfully acquired during 8-12-second respiratory pauses. This simple, reproducible technique produced thin-section CT images that were clearer and more clinically useful than those obtained during quiet tidal breathing.

A multicenter randomized masked comparison trial of synthetic surfactant versus calf lung surfactant extract in the prevention of neonatal respiratory distress syndrome.

OBJECTIVE: To compare the efficacy and safety of a synthetic surfactant (Exosurf Neonatal, Burroughs Wellcome Co) and a surfactant extract of calf lung lavage (Infasurf, IND #27,169, ONY, Inc) in the prevention of neonatal respiratory distress syndrome (RDS). DESIGN AND SETTING: Ten-center randomized masked comparison trial. PATIENTS: Premature infants (n = 871) <29 weeks gestational age by best obstetric estimate. INTERVENTIONS: Infants were randomly assigned to a course of treatment with Exosurf Neonatal (n = 438) or Infasurf (n = 433) at birth, and if still intubated, at 12 and 24 hours of age. Crossover treatment was allowed within 72 hours of age if severe respiratory failure (defined as two consecutive a/A PO2 ratios

Asymptomatic, palpable, anterior chest wall lesions in children: is cross-sectional imaging necessary?

PURPOSE: To review results from cross-sectional imaging studies performed to evaluate asymptomatic anterior chest wall lesions in children. MATERIALS AND METHODS: All magnetic resonance (MR) images or computed tomographic (CT) scans of the chest obtained from 1989 to 1996 for evaluation of asymptomatic, palpable, focal, anterior chest wall lesions in otherwise healthy children were reviewed. Fifty-one children were considered for the study. Findings from 27 examinations in 27 children (13 underwent MR imaging, and 14 underwent CT) were included in the study. All children had normal radiographs of the region. Twenty-four patients did not meet the inclusion criteria and were excluded. RESULTS: The cause of the lesion palpated at physical examination was identified in 26 of 27 patients: prominent anterior convex ribs in 10 patients; "tilted" sternum in six; prominent asymmetric costal cartilage in four; bifid rib in one; and well-defined, small (< 1-cm) subcutaneous nodule adjacent to costal cartilage in five. One examination demonstrated no abnormality. Of the 27 patients, none required treatment. CONCLUSION: All palpable, asymptomatic, anterior chest wall lesions were benign and usually related to normal variations in the bone or cartilage of the chest wall. The low yield of cross-sectional imaging performed for evaluation of these asymptomatic "bumps" should be considered when decisions are made with regard to imaging.

Comparison between morphologic changes seen on high-resolution CT and regional pulmonary perfusion seen on SPECT in patients with cystic fibrosis.

OBJECTIVE: To evaluate the relationship between morphologic findings seen on high-resolution computed tomography (HRCT) of the lung and regional lung perfusion depicted on single photon-emission computed tomography (SPECT) pulmonary perfusion imaging in patients with cystic fibrosis. MATERIALS AND METHODS: Ten HRCT and 10 technetium-99 m macroaggregated albumin SPECT pulmonary perfusion imaging studies were performed on eight young adult patients who were considered to be clinically well and have mild to moderate cystic fibrosis. HRCT scans of the chest were evaluated using a CT scoring system which included grading of bronchiectasis, peribronchial thickening, hyperlucency, bullae, collapse/consolidation, and mucus plugging. Each lung was divided into six anatomic zones which were independently scored. A lung perfusion score (between 0 and 100), reflecting the percentage of compromised lung, was estimated for each zone. Axial lung perfusion SPECT images were matched anatomically to HRCT images. Lung function was considered compromised when the counts per pixel were less than 25 % of the count level seen in an area of the same patient's lung which was judged to be normal. RESULTS: There was a statistically significant relationship (P = 0.0001) between HRCT total scores and SPECT lung perfusion scores as well as between hyperlucency scores by HRCT and the SPECT lung perfusion scores. However, the HRCT score was a poor predictor of the lung perfusion score in zones with intermediate HRCT scores, which constituted 106 of 120 zones. CONCLUSION: Morphologic changes depicted by HRCT correlate with decreased lung pefusion on SPECT. However, HRCT changes accurately predict regional lung function only in the most normal and severely diseased lung zones.

Detection of coronary artery calcium to differentiate patients with early coronary atherosclerosis from luminally normal arteries.

Patients with angiographic evidence of early coronary atherosclerosis (<50% diameter stenosis) have a poorer prognosis than those with normal arteries and may benefit from more aggressive interventions targeted toward the primary prevention of cardiovascular disease. Using a calcium score of 5, fast computed tomography was able to identify 59% of patients with early atherosclerosis, while excluding 87% of patients with smooth, luminally normal coronary arteries.

A multicenter randomized, masked comparison trial of natural versus synthetic surfactant for the treatment of respiratory distress syndrome.

OBJECTIVE: To compare the efficacy and safety of two surfactant preparations in the treatment of respiratory distress syndrome (RDS). METHODS: We conducted a randomized, masked comparison trial at 21 centers. Infants with RDS who were undergoing mechanical ventilation were eligible for treatment with two doses of either a synthetic (Exosurf) or natural (Infasurf) surfactant if the ratio of arterial to alveolar partial pressure of oxygen was less than or equal to 0.22. Crossover treatment was allowed within 96 hours of age if severe respiratory failure (defined as two consecutive arterial/alveolar oxygen tension ratios < or = 0.10) persisted after two doses of the randomly assigned surfactant. Four primary outcome measures of efficacy (the incidence of pulmonary air leak (< or = 7 days); the severity of RDS; the incidence of death from RDS; and the incidence of survival without bronchopulmonary dysplasia (BPD) at 28 days after birth) were compared by means of linear regression techniques. RESULTS: The primary analysis of efficacy was performed in 1033 eligible infants and an analysis of safety outcomes in the 1126 infants who received study surfactant. Preentry demographic characteristics and respiratory status were similar for the two treatment groups, except for a small but significant difference in mean gestational age (0.5 week) that favored the infasurf treatment group. Pulmonary air leak (< or = 7 days) occurred in 21% of Exosurf- and 11% of infasurf-treated infants (adjusted relative risk, 0.53; 95% confidence interval, 0.40 to 0.71; p < or = 0.0001). During the 72 hours after the initial surfactant treatment, the average fraction of inspired oxygen (+/-SEM) was 0.47 +/- 0.01 for Exosurf- and 0.39 +/- 0.01 for infasurf-treated infants (difference, 0.08; 95% confidence interval, 0.06 to 0.10; p < 0.0001); the average mean airway pressure (+/-SEM) was 8.6 +/- 0.1 cm H2O; for Exosurf- and 7.2 +/- 0.1 cm H2O for Infasurf-treated infants (difference, 1.4 cm H2O; 95% confidence interval, 1.0 to 1.8 cm H2O; p < 0.0001). The incidences of RDS-related death, total respiratory death, death to discharge, and survival without bronchopulmonary dysplasia at 28 days after birth did not differ. The number of days of more than 30% inspired oxygen and of assisted ventilation, but not the duration of hospitalization, were significantly lower in Infasurf-treated infants. CONCLUSION: Compared with Exosurf, Infasurf provided more effective therapy for RDS as assessed by significant reductions in the severity of respiratory disease and in the incidence of air leak complications.

Prognostic value of sonography in childhood nephrotic syndrome.

This retrospective case review of 43 children with primary nephrotic syndrome was designed to evaluate the relationship among renal ultrasound findings at presentation, subsequent corticosteroid responsiveness and histological diagnoses. Fifty-one percent of patients had abnormal sonograms; nephromegaly was present in 42% and increased renal echogenicity in 35%. There was no relationship between nephromegaly and either response to corticosteroids or specific glomerular lesions causing nephrosis. Although the presence of echogenic kidneys did not denote a particular type of renal disease, it was significantly more frequent in corticosteroid-resistant than in corticosteroid-responsive patients (62% vs. 18%, P < 0.05). We conclude that increased renal echogenicity at time of presentation is a possible indicator of corticosteroid resistance in children with primary nephrotic syndrome.

Fast computed tomography detection of coronary calcification in the diagnosis of coronary artery disease. Comparison with angiography in patients < 50 years old.

BACKGROUND: The predominant cause of coronary artery calcification is atherosclerosis. Although fast x-ray computed tomography (CT) has been demonstrated to be a sensitive technique to detect coronary calcification, the increasing prevalence of calcification with age has been associated with a low specificity for identifying obstructive atherosclerosis. We hypothesized that the specificity of this test would be improved in a younger patient population, making it more useful in the diagnosis of coronary artery disease. METHODS AND RESULTS: We compared fast CT-detected calcification with coronary angiography in 106 patients under the age of 50 years. Nonenhanced fast CT scans consisting of 20 contiguous 3-mm tomograms of the proximal coronary arteries were obtained during a single breath hold. A positive scan was defined as 4 contiguous voxels (> or = 1 mm2) of density > 130 Hounsfield units in the region of the epicardial coronary arteries. Calcification detected by fast CT had an 85% sensitivity to predict patients with significant coronary artery disease (> or = 50% diameter stenosis), with a specificity of 45%. Although the sensitivity to detect multivessel disease was 94%, the sensitivity to detect single-vessel disease was 75%. Changing the threshold for defining a positive fast CT scan from 4 to 2 contiguous voxels produced a small improvement in sensitivity, to 88%, but reduced specificity to 36%. CONCLUSIONS: Although the specificity to detect angiographically significant coronary disease with fast CT improves in a younger patient population, it continues to be relatively low. In contrast to older patient populations, a small but significant number of patients < 50 years old with angiographically significant coronary artery disease do not have coronary calcification demonstrated by fast CT. Thus, caution should be used in excluding significant coronary artery disease on the basis of a negative fast CT study.

Demonstration of renal tubular flow by selective angiographic computed tomography.

A high-speed computed tomography scanner was used to study the bulk flow of a small bolus of nonionic contrast medium through the renal tubules of five dogs. A 0.5-mL bolus of iohexol 300 (150 mg iodine) was injected rapidly into the renal artery, and transverse images of the kidney were obtained at 15-second intervals over 300 seconds. The mean attenuation values measured in regions of interest in the papilla and the cortex were displayed as a function of time. Curves from the papillary regions of interest showed two peaks, the first corresponding to the passage of the bolus through the loops of Henle that extend into the papilla and the second to the passage of the bolus through the terminal collecting tubules. The cortical regions of interest showed the cortical return peak, which corresponded to the passage of the bolus through the distal convoluted tubules. The peaks generated by this method can be used to measure the transit times of the bolus from the glomeruli to the loops of Henle in the papilla, from the loops of Henle to the distal convoluted tubules, and from the distal convoluted tubules to the distal collecting tubules. The mean total transit time in dehydrated dogs was 169 seconds. The method is compared with contrast-enhanced magnetic resonance imaging (with gadolinium diethylenetriaminepentaacetic acid), which has been used by other researchers for the same purpose.

Pulmonary arterial elasticity in awake dogs.

We measured the relationship between pulmonary arterial pressure (Ppa), diameter (D), and length of a segment of the main pulmonary artery (MPA) in chronically instrumented conscious dogs breathing spontaneously (CCC). There were no physiologically significant changes in Ppa or D in the CCC dogs postoperatively, and the cross-sectional MPA shape measured by fast computed tomography was nearly circular. These results suggest that the MPA was not distorted by chronic instrumentation. We compared measurements made in the CCC dogs with previous measurements in acutely instrumented anesthetized dogs with open chests (AAO). The elasticity of MPA in the CCC animals was frequency dependent between 1 and 14 Hz and was similar to that in the AAO dogs. Oscillations of D preceded Ppa at cardiac frequencies in the AAO animals, but the D and Ppa oscillations were in phase in the CCC animals. The oscillations of length relative to D were significantly less in the CCC than in the AAO dogs. We conclude that, with limitations, the hemodynamic properties of the MPA can be measured in the CCC subjects. We suggest that the discrepancies between the AAO and CCC dogs can be attributed to differences in extrinsic loading of the MPA.

Vascular exchange in the kidney. Regional characterization by multiple indicator tomography.

In previous work with the method of multiple indicator dilution (MID), we have established that a spatially distributed model of transcapillary exchange proposed by Goresky, Ziegler, and Bach (GZB) accurately describes, at the in vivo whole-organ level, the handling of extracellular indicators in the canine renal cortex. To date, however, it has not been possible to assess the key hypothesis that GZB corresponds to the actual local mechanism of exchange in vivo and is not just a compact summary of the kidney's average whole-organ behavior. By adapting the MID method to high speed computed tomography (CT), we are now able to report that the GZB mechanism is an accurate description of renal cortical transcapillary exchange down to volumes of cortical tissue comprising no more than a few per cent of the total cortical mass, i.e., containing no more than a few thousand nephrons. A small bolus of iohexol (radiopaque extracellular indicator) or iodipamide ethyl ester microparticles (radiopaque plasma indicator) injected into the renal artery was followed by CT as it passed through the kidney and into the renal vein. Time-attenuation value curves of the two contrast media obtained from the renal vein and from regions of interest in the cortex were then modeled with the GZB mechanism and with a more complex formulation that includes GZB as a limiting case. When applied to the data, the models converged to GZB as the best fit for each region examined. The GZB mechanism is found to provide excellent agreement with the regional data.