Weight-based, low-dose pediatric whole-body PET/CT protocols.

UNLABELLED: Adult PET/CT acquisition protocols need to be modified for pediatric imaging to minimize the radiation dose while maintaining diagnostic utility. We developed pediatric PET/CT acquisition protocols customized to patient weight and estimated the dosimetry and cancer risk of these low-dose protocols to communicate basic imaging risks. METHODS: Protocols were developed for whole-body (18)F-FDG imaging of patients in PET mode with a weight-based injected activity (5.3 MBq/kg) and acquisition times (3-5 min/field of view) and for CT for attenuation correction and localization with a weight-based tube current ranging from 10 to 40 mAs. Patients were categorized on the basis of the Broselow-Luten color-coded weight scale. Dosimetry and radiation-induced cancer risk for the PET and CT acquisition in each category were derived from mean patient sizes and the interpolation of factors from accepted patient models. RESULTS: Whole-body pediatric PET/CT protocols require the customization of PET-acquisition settings and task-specific selection of CT technique. The proposed weight-based protocols result in an approximate effective dose ranging from 8.0 mSv for a 9-kg patient up to 13.5 mSv for a 63-kg patient. The radiation dose from the proposed protocols is 20%-50% (depending on patient weight), the dose from PET/CT protocols that use a fixed CT technique of 120 mAs and 120 kVp. The approximate, conservative estimate of additional lifetime attributable risk (LAR) of cancer incidence for females using the proposed protocols was approximately 3 in 1,000, with a variation of 18% across patient categories. For males, the additional LAR of cancer incidence was approximately 2 in 1,000, with a variation of 16% across categories. CONCLUSION: Low-dose PET/CT protocols for 11 patient weight categories were developed. The proposed protocols offer an initial set of acquisition parameters for pediatric PET/CT. The use of multiple categories allows for the continued refinement of dose-reduction parameters to minimize dose while maintaining image quality across the range of pediatric patient sizes.

MDCT diagnosis of the child with posterior plagiocephaly.

OBJECTIVE: In this article, we review the normal anatomy and development of the posterior skull base and describe distinguishing imaging features of the two most common causes of posterior plagiocephaly: posterior deformational plagiocephaly and unilateral lambdoid synostosis. We also describe three unusual cases of posterior plagiocephaly, including asymmetric premature fusion of the anterior and posterior intraoccipital synchondroses, with diagnoses enabled by volume-reformatted MDCT. CONCLUSION: Three-dimensional reformatted MDCT enables accurate diagnosis of common and rare causes of posterior plagiocephaly in children.

Multidetector CT angiography of pediatric vascular malformations and hemangiomas: utility of 3-D reformatting in differential diagnosis.

BACKGROUND: Vascular malformations can be difficult to diagnose and classify. Accurate classification is important because treatments and prognosis vary based on the type of lesion. Diagnosis is based on a combination of clinical features with a variety of imaging techniques, including US, MRI/MRA, CT, and conventional angiography. OBJECTIVE: We hypothesized that imaging features seen on 3-D reformatted images obtained with multidetector CT angiography (CTA) would aid in differential diagnosis of types of vascular anomalies. MATERIALS AND METHODS: We retrospectively reviewed CT scans of 11 patients with vascular lesions and pathologically proven diagnoses in which 3-D reformatting was obtained. RESULTS: The 3-D images accurately diagnosed hemangiomas and lymphangiomas in all cases, in contrast to diagnosis by clinical criteria and planar CT, which was difficult or inaccurate. The 3-D CTA did not aid in the distinction between venous malformations and arteriovenous malformations (AVM), which appeared similar. CONCLUSIONS: Our preliminary observations suggest that volume-rendered reformatting is helpful in categorizing clinically significant vascular head and neck lesions, resulting in more diagnostic value than planar CT imaging alone. In particular, 3-D CTA might allow accurate differentiation of hemangiomas from AVM, and of lymphangiomas from other types of lesions, which was, in our series, not possible using clinical examination or conventional planar CT angiography.

Three-dimensional CT angiography imaging of vascular tumors of the head and neck.

OBJECTIVE: To evaluate the utility of three-dimensional (3D) computerized tomography angiography (CTA) in head and neck vascular anomalies. DESIGN: Prospective case series. METHODS: A consecutive series of cases of patients with distinct types of vascular anomalies (i.e. hemangioma, arteriovenous malformation, venous malformation and lymphatic malformation) were obtained through CT multislice scanner and analyzed with Vitrea 2 software (Vital Images Inc., Plymouth, MN). RESULTS: CTA was safe and successful in describing 3D vascular anatomy of a variety of vascular lesions. CONCLUSIONS: Three-dimensional CTA allows detailed description of vascular lesions of the head and neck and offers another effective means of imaging these complex lesions.

Rapid computed tomography technique to measure ventricular volumes in the child with suspected ventriculoperitoneal shunt failure I. Validation of technique with a dynamic phantom.

OBJECTIVES: Assessment of ventricular volume change is critical and can be difficult in the child with suspected shunt failure. Objective techniques described to measure ventricular volumes have used limited anatomic sampling or have been computationally intensive. Phantoms used to evaluate these techniques have used static volumes. The purpose of this study was to construct a computed tomography (CT) phantom to simulate changing ventricular volumes and to evaluate a new program to measure volumes. METHODS: The phantom is 5 Foley catheters embedded in gelatin. The balloons were filled and then scanned at 15-mL increments from 0-300 mL. The program measures the voxels of specified density within a larger volume created by applying a region of interest to a stacked volume. Calculated volumes and percent changes were compared with actual volumes and percent changes. RESULTS: Calculated volumes were consistently 7%-9% (mean: -7.8%) less than actual injected volumes across the entire 0- to 300-mL range. For true changes between -50% and +50%, all calculated changes were within +/-2.5% points of true percent change; for true changes between +50% and +100%, all calculated changes were within +/-5% points of true percent change. CONCLUSIONS: A dynamic CT phantom simulating changing ventricular volumes can be constructed from readily available materials. A new volumetric program accurately measures ventricular volumes and percent change from baseline across a wide range of volumes.

Rapid computed tomography technique to measure ventricular volumes in the child with suspected ventriculoperitoneal shunt failure II. Clinical application.

OBJECTIVES: Assessment of ventricular volume change is critical in the child with suspected shunt failure. Minimal increases may represent high pressures in the child with reduced ventricular compliance but are difficult to detect subjectively. Objective techniques described limit anatomic sampling and are time intensive. The purpose of this study was to develop a rapid technique to measure ventricular volumes in children with suspected shunt failure. METHODS: Ventricular volumes were calculated in 12 children with baseline and emergent computed tomography scans performed for suspected shunt failure. Volumes and percent interval changes were correlated with clinical course. Two observers performed the volume analysis blinded to the clinical information; 1 observer performed the analysis twice. Time to perform the analysis was recorded for 5 studies. RESULTS: The intraobserver and interobserver correlation coefficients were 0.99 and 0.96/0.97, respectively. The mean time to perform the analysis was 2 minutes 42 seconds. Median percent change in patients with and without shunt obstruction was +50% (range: +24%-+367%) and +2% (range: -22%-+36%), respectively. Among patients subjectively read as having stable ventricular sizes, volume changes of -11% to +32% were calculated. CONCLUSIONS: The technique has excellent intra- and interobserver correlation and is rapidly performed. The range of percent volume changes between patients with and without shunt malfunction overlaps. Subjective assessment of ventricular changes is significantly less sensitive than the volume calculation technique. The technique may be most useful in patients with decreased ventricular compliance in whom small interval changes may represent large pressure increases.