Robert C. Orth

C-arm Cone-beam CT: General Principles and Technical Considerations for Use in Interventional Radiology

Digital flat-panel detector cone-beam computed tomography (CBCT) has recently been adapted for use with C-arm systems. This configuration provides projection radiography, fluoroscopy, digital subtraction angiography, and volumetric computed tomography (CT) capabilities in a single patient setup, within the interventional suite. Such capabilities allow the interventionalist to perform intraprocedural volumetric imaging without the need for patient transportation. Proper use of this new technology requires an understanding of both its capabilities and limitations. This article provides an overview of C-arm CBCT with particular attention to trade-offs between C-arm CBCT systems and conventional multi-detector CT.

Three-Dimensional C-arm Cone-beam CT: Applications in the Interventional Suite

C-arm cone-beam computed tomography (CT) with a flat-panel detector represents the next generation of imaging technology available in the interventional radiology suite and is predicted to be the platform for many of the three-dimensional (3D) roadmapping and navigational tools that will emerge in parallel with its integration. The combination of current and unappreciated capabilities may be the foundation on which improvements in both safety and effectiveness of complex vascular and nonvascular interventional procedures become possible. These improvements include multiplanar soft tissue imaging, enhanced pretreatment target lesion roadmapping and guidance, and the ability for immediate multiplanar posttreatment assessment. These key features alone may translate to a reduction in the use of iodinated contrast media, a decrease in the radiation dose to the patient and operator, and an increase in the therapeutic index (increase in safety-vs-benefit ratio). In routine practice, imaging information obtained with C-arm cone-beam CT provides a subjective level of confidence factor to the operator that has not yet been thoroughly quantified.

Prospective Comparison of MR Imaging and US for the Diagnosis of Pediatric Appendicitis

PURPOSE To prospectively compare nonenhanced magnetic resonance (MR) imaging and ultrasonography (US) for the diagnosis of pediatric appendicitis. MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained from the patients parent or guardian. Eighty-one patients (34 male, 47 female; mean age, 12.3 years ± 3.5 [standard deviation]; range, 4-17 years) were enrolled in this prospective study. All patients underwent right lower quadrant US and nonenhanced, nonsedated abdominopelvic MR imaging examinations. Two pediatric radiologists blinded to US results independently reviewed the MR images. MR imaging and US findings were designated positive, negative, or equivocal for acute appendicitis. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for MR imaging and US and compared by using two-sided McNemar test or the score statistics specified by Leisenring. Kappa statistics were generated to determine intertechnique agreement between MR imaging and US and interobserver agreement between the two primary MR imaging readers. RESULTS Thirty (37%) patients had pathologically proved acute appendicitis. When equivocal interpretations were designated positive, sensitivity was 93.3% for MR imaging (95% confidence interval [CI]: 77.9%, 99.2%) and 90.0% for US (95% CI: 73.5%, 97.9%), P > .99; specificity was 98% for MR imaging (95% CI: 89.6%, 100%) and 86.3% for US (95% CI:73.7%, 94.3%), P = .03; PPV was 96.5% for MR imaging (95% CI: 82.2%, 99.9%) and 79.4% for US (95% CI: 62.1%, 91.3%), P = .007; and NPV was 96.2% for MR imaging (95% CI: 86.8%, 99.5%) and 93.6% for US (95% CI: 82.4%, 98.7%), P = .45, with substantial intertechnique (κ = 0.77; 95% CI: 0.63, 0.90) and interobserver (κ = 0.76; 95% CI: 0.61, 0.91) agreement. When equivocal interpretations were designated negative, MR imaging sensitivity, specificity, PPV, and NPV were unchanged. For US, sensitivity was 86.7% (95% CI: 69.3%, 96.2%), P = .5; specificity was 100% (95% CI: 93.0%, 100%), P > .99; PPV was 100% (95% CI: 86.8%, 100%), P = .31; and NPV was 92.7% (95% CI: 82.4%, 98.0%), P = .16, with almost perfect intertechnique (κ = 0.92; 95% CI: 0.83, 1.00) and substantial interobserver (κ = 0.72; 95% CI: 0.58, 0.87) agreement. CONCLUSION Nonenhanced MR imaging demonstrates high diagnostic performance similar to that of US for suspected pediatric appendicitis.

Community-Acquired Staphylococcal Musculoskeletal Infection in Infants and Young Children: Necessity of Contrast-Enhanced MRI for the Diagnosis of Growth Cartilage Involvement

OBJECTIVE Previous studies have reported that contrast-enhanced sequences do not increase the sensitivity of MRI for the diagnosis of pediatric osteomyelitis and are not needed in the absence of edema on unenhanced MRI sequences. Invasive skeletal infections due to community-acquired Staphylococcus aureus are increasingly encountered in infants and young children and have a proclivity for involvement of both the unossified growth cartilage and the metadiaphyseal bone marrow of the extremities. The study objective is to assess the diagnostic efficacy of contrast-enhanced and unenhanced MRI sequences for the diagnosis of community-acquired S. aureus extremity skeletal infection in infants and young children. MATERIALS AND METHODS A retrospective review was conducted of the clinical charts and imaging studies of patients younger than 18 months diagnosed with invasive community-acquired S. aureus skeletal infections from 2001 to 2009 at a large childrens hospital. Sensitivity was calculated for the detection of skeletal infection on contrast-enhanced and unenhanced MRI sequences. The p values were calculated using the Fisher exact score method. The kappa value for interobserver reliability was determined. RESULTS Community-acquired S. aureus skeletal infections were noted in 34 extremity sites in 25 patients, five of whom had more than one site of disease. The affected skeletal sites were metaphyseal or metadiaphyseal bone marrow only in 16 cases (47%), unossified growth cartilage only in nine cases (26%), and both the unossified growth cartilage and metaphyseal or metadiaphyseal bone marrow in nine cases (26%). In seven of the nine cases of isolated involvement of the unossified growth cartilage, the cartilage appeared normal on unenhanced sequences and the diagnosis was made only by the demonstration of hypoenhancing or nonenhancing foci in the cartilage after gadolinium-based contrast agent administration. In five of the nine cases of infection of both the unossified growth cartilage and metaphyseal or metadiaphyseal bone marrow, neither the cartilage nor bone marrow appeared abnormal on unenhanced sequences. Therefore, 12 cases of skeletal infection would have been missed without the inclusion of contrast-enhanced sequences. Follow-up extremity radiographs were available for 10 patients, eight (80%) of whom exhibited growth disturbances. CONCLUSION Skeletal infection caused by community-acquired S. aureus in infants and young children manifests differently than in older children, including a propensity for involvement of the unossified growth cartilage and potentially occult nature of both cartilage and bone marrow involvement on unenhanced MRI sequences.

Performance of CT Examinations in Children With Suspected Acute Appendicitis in the Community Setting: A Need for More Education

OBJECTIVE Despite a recent focus on the preferential use of ultrasound over CT for pediatric appendicitis, most children transferred from community hospitals still undergo diagnostic CT scans. The purpose of this study was to evaluate CT techniques performed for children with acute appendicitis at nonpediatric treatment centers. MATERIALS AND METHODS All patients treated for acute appendicitis at our tertiary-care pediatric hospital from July 1, 2011, through June 30, 2012, were identified. Patient demographics, imaging modality used to diagnoses appendicitis (CT or ultrasound), location (home or referral institution), and CT technique parameters were collected. The estimated mean organ radiation dose, number of imaging phases, and use of contrast media were evaluated at home and referral institutions. RESULTS During the study period, 1215 patients underwent appendectomies after imaging, with 442 (36.4%) imaged at referral facilities. Most referral patients received a diagnosis by CT (n=384, 87%), compared with 73 of 773 (9.4%) who received a diagnosis by CT at the home institution. The estimated mean (±SD) organ radiation dose was not statistically significantly different between home and referral institutions (13.5±7.3 vs 12.9±6.4 mGy; p=0.58) for single-phase examinations. Of 384 referral patients, 344 had images available for review. In total, 40% (138/344) of patients from referral centers were imaged with suboptimal CT techniques: 50 delayed phase only, 52 dual phase (eight of which were imaged twice in delayed phase), eight triple phase, and 36 without IV contrast agent. CONCLUSION CT parameters and radiation doses from single-phase examinations in children with appendicitis were similar at nonpediatric treatment centers and a tertiary care childrens hospital. Future educational outreach should focus on optimizing other technical parameters.

Radiographic screening of infants and young children with genetic predisposition for rare malignancies: DICER1 mutations and pleuropulmonary blastoma

OBJECTIVE The purpose of this study was to compare the risks of radiation in screening strategies using chest radiographs and CT to detect a rare cancer in a genetically predisposed population against the risks of undetected disease. MATERIALS AND METHODS A decision analytic model of diagnostic imaging screening strategies was built to predict outcomes and cumulative radiation doses for children with DICER1 mutations screened for pleuropulmonary blastoma. Screening strategies compared were chest radiographs followed by chest CT for a positive radiographic result and CT alone. Screening frequencies ranged from once in 3 years to once every 3 months. BEIR VII (model VII proposed by the Committee on the Biological Effects of Ionizing Radiation) risk tables were used to predict excess cancer mortality for each strategy, and the corresponding loss of life expectancy was calculated using Surveillance Epidemiologic and End Results (SEER) statistics. Loss of life expectancy owing to undetected progressive pleuropulmonary blastoma was estimated on the basis of data from the International Pleuropulmonary Blastoma Registry. Sensitivity analysis was performed for all model parameters. RESULTS Loss of life expectancy owing to undetected disease in an unscreened population exceeded that owing to radiation-induced cancer for all screening scenarios investigated. Increases in imaging frequency decreased loss of life expectancy for the combined (chest radiographs and CT) screening strategy but increased that for the CT-only strategy. This was because loss of life expectancy for combined screening is dominated by undetected disease, whereas loss of life expectancy for CT screening is dominated by radiation-induced cancers. CONCLUSION Even for a rare disease such as pleuropulmonary blastoma, radiographic screening of infants and young children with cancer-predisposing mutations may result in improved life expectancy compared with the unscreened population. The benefit of screening will be greater for diseases with a higher screening yield.

Endpoints for Hemodialysis Access Procedures: Correlation between Fistulography and Intraaccess Blood Flow Measurements

PURPOSE The success of percutaneous interventions on stenotic hemodialysis prosthetic grafts and autogenous fistulas is assessed by comparing vessel diameter before and after treatment. These changes do not correlate with gold standard access blood flow (ABF) measurements obtained during hemodialysis. The AngioFlow (AngioDynamics, Inc, Queensbury, New York) calculates real-time blood flow through access circuits and may provide more physiologically relevant data in the interventional suite. This study compares angiographic vessel diameter and access circuit flow rates obtained with the AngioFlow Meter before and after percutaneous interventions on stenotic hemodialysis prosthetic grafts and autogenous fistulas ABF measurements obtained during hemodialysis. MATERIALS AND METHODS Angiographic images and AngioFlow measurements for 76 procedures in 35 patients undergoing hemodialysis with arteriovenous grafts or fistulas were analyzed retrospectively. Correlations between ABF, fistulography, and AngioFlow measurements before and after treatment were computed. Regression analyses of AngioFlow measurements and measurements after ABF were performed to account for confounding factors. Time to failure of treatment was modeled in first-time patients stratified by AngioFlow values obtained after treatment. Only patients with ABF measurements obtained within 5 weeks of intervention were included. RESULTS Correlations between initial ABF and fistulography measurement (ρ = 0.781), initial ABF and AngioFlow (ρ = 0.675), and final AngioFlow and ABF measurement (ρ = 0.798) were statistically significant. The correlation between final ABF and AngioFlow was significantly stronger than final ABF and fistulography (difference = 0.418, 95% bootstrap confidence interval [CI] [0.054, 0.914]). AngioFlow values and access survival after treatment did not show significant correlation. CONCLUSIONS AngioFlow measurements performed after treatment correlate more strongly with hemodialysis ABF values than fistulography measures. Further studies are needed to determine the target AngioFlow value obtained after treatment that is associated with the greatest survival benefit for access circuits.

Renal Ultrasound for Infants Younger Than 2 Months With a Febrile Urinary Tract Infection

OBJECTIVE The purpose of this study is to determine the performance of renal ultrasound for detecting vesicoureteral reflux (VUR) and obstructive uropathies in infants younger than 2 months with a febrile urinary tract infection (UTI). MATERIALS AND METHODS We performed a retrospective cohort study of infants younger than 2 months with fever and culture-proven UTI presenting from July 1, 2008, through December 31, 2011, with renal ultrasound and voiding cystourethrogram (VCUG) performed within 30 days of UTI diagnosis. Two pediatric radiologists independently reviewed the renal ultrasound and VCUG findings. Results of the renal ultrasound were deemed abnormal if collecting system dilation, renal size asymmetry, collecting system duplication, urothelial thickening, ureteral dilation, or bladder anomalies were present. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of renal ultrasound were calculated using VCUG as reference standard. RESULTS Of the 197 patients included (mean [SD] age, 33 [ 15 ] days; male-to-female ratio, 2:1), 25% (n = 49) had VUR grades I-V, with 16% (n = 31) having VUR grades III-V and 8% (n = 15) having VUR grades IV-V. For grades I-V VUR, sensitivity was 32.7% (95% CI, 20.0-47.5%), specificity was 69.6% (95% CI, 61.5-76.9%), PPV was 26.2% (95% CI, 15.8-39.1%), and NPV was 75.7% (95% CI, 67.6-82.7%). For grades III-V VUR, sensitivity was 51.6% (95% CI, 33.1-69.9%), specificity was 72.9% (95% CI, 65.5-79.5%), PPV was 26.2% (95% CI, 15.8-39.1%), and NPV was 89.0% (95% CI, 82.5-93.7%). For grades IV-V VUR, sensitivity was 86.7% (95% CI, 59.5-98.3%), specificity was 73.6% (95% CI, 66.6-79.9%), PPV was 21.3% (95% CI, 11.9-33.7%), and NPV was 98.5% (95% CI, 94.8-99.8%). No obstructive uropathies were diagnosed by VCUG in patients with normal renal ultrasound findings. CONCLUSION In infants younger than 2 months, a normal renal ultrasound makes the presence of grades IV and V VUR highly unlikely but does not rule out lower grades of VUR.

Isolated costal cartilage fracture: an unusual cause of an anterior chest mass in a toddler

A 17-month-old boy presented with a palpable anterior chest wall mass and was evaluated by chest radiography, sonography, and MRI. No history of trauma was provided initially. Sonography and MRI showed a costal cartilage fracture with overlying hematoma. Identification of a fracture isolated to the costal cartilage is rare and this is a unique case among children. In the appropriate clinical setting, costal cartilage fractures can be confirmed by sonography alone, and follow-up assessment can be based on clinical evaluation without the need for additional cross-sectional imaging.

The pediatric knee

Knee pain is a common problem in children and adolescents, and MRI of the knee is the most commonly performed pediatric cross-sectional musculoskeletal imaging exam. The purpose of this pictorial review is to highlight differences between adult and pediatric knee imaging with an emphasis on normal developmental variants, injury and disease patterns unique to children and adolescents, and differences in response and presentation to conditions affecting both adults and children.