Ethan A. Smith

Developing a Clinical Decision Model: MR Spectroscopy to Differentiate Between Recurrent Tumor and Radiation Change in Patients with New Contrast-Enhancing Lesions

OBJECTIVE Differentiation between recurrent neoplasm and postradiation change in patients previously treated for primary brain tumors is often difficult based on imaging features alone. The purpose of this study was to develop a method using alterations in the ratios of standard brain metabolites-choline (Cho), creatine (Cr), and N-acetylaspartate (NAA)-to predict the probability of tumor recurrence in patients previously treated for brain tumors with new contrast-enhancing lesions. MATERIALS AND METHODS Thirty-three patients who had undergone treatment for primary brain tumors in whom routine MRI showed new contrast-enhancing lesions were retrospectively studied. The final diagnosis was assigned using histopathology (n = 13) or imaging follow-up (n = 20; range, 2-27 months). Ratios of three metabolites (Cho, Cr, and NAA) were calculated, and the results were correlated with the final diagnosis using a Wilcoxons rank sum analysis. A logistic regression model was then used to create a prediction model based on the most statistically significant ratio. RESULTS Elevations of the metabolic ratios Cho/Cr (p < 0.001) and Cho/NAA (p < 0.001) and a decrease in the ratio NAA/Cr (p = 0.018) were found in patients with recurrent tumor (n = 20) versus those with postradiation change (n = 13). A prediction model using the Cho/NAA ratio yielded a sensitivity of 85%, a specificity of 69.2%, and an area under the receiver operating characteristic curve of 0.92. CONCLUSION An elevated Cho/NAA ratio correlated with evidence of tumor recurrence and allowed creation of a prediction rule to aid in lesion classification. The results suggest that MR spectroscopy is a useful tool in assigning patients with nonspecific enhancing lesions to either invasive biopsy or conservative management.

Model-based Iterative Reconstruction: Effect on Patient Radiation Dose and Image Quality in Pediatric Body CT

PURPOSE To retrospectively compare image quality and radiation dose between a reduced-dose computed tomographic (CT) protocol that uses model-based iterative reconstruction (MBIR) and a standard-dose CT protocol that uses 30% adaptive statistical iterative reconstruction (ASIR) with filtered back projection. MATERIALS AND METHODS Institutional review board approval was obtained. Clinical CT images of the chest, abdomen, and pelvis obtained with a reduced-dose protocol were identified. Images were reconstructed with two algorithms: MBIR and 100% ASIR. All subjects had undergone standard-dose CT within the prior year, and the images were reconstructed with 30% ASIR. Reduced- and standard-dose images were evaluated objectively and subjectively. Reduced-dose images were evaluated for lesion detectability. Spatial resolution was assessed in a phantom. Radiation dose was estimated by using volumetric CT dose index (CTDI(vol)) and calculated size-specific dose estimates (SSDE). A combination of descriptive statistics, analysis of variance, and t tests was used for statistical analysis. RESULTS In the 25 patients who underwent the reduced-dose protocol, mean decrease in CTDI(vol) was 46% (range, 19%-65%) and mean decrease in SSDE was 44% (range, 19%-64%). Reduced-dose MBIR images had less noise (P > .004). Spatial resolution was superior for reduced-dose MBIR images. Reduced-dose MBIR images were equivalent to standard-dose images for lungs and soft tissues (P > .05) but were inferior for bones (P = .004). Reduced-dose 100% ASIR images were inferior for soft tissues (P < .002), lungs (P < .001), and bones (P < .001). By using the same reduced-dose acquisition, lesion detectability was better (38% [32 of 84 rated lesions]) or the same (62% [52 of 84 rated lesions]) with MBIR as compared with 100% ASIR. CONCLUSION CT performed with a reduced-dose protocol and MBIR is feasible in the pediatric population, and it maintains diagnostic quality.

Cross-Sectional Imaging of Acute and Chronic Gallbladder Inflammatory Disease

OBJECTIVE The purpose of this article is to provide a comprehensive review of the clinical and cross-sectional imaging features of a variety of acute and chronic gallbladder inflammatory diseases. CONCLUSION Inflammatory gallbladder diseases are a common source of abdominal pain and cause considerable morbidity and mortality. Although acute uncomplicated cholecystitis and chronic cholecystitis are frequently encountered, numerous other gallbladder inflammatory conditions may also occur that can be readily diagnosed by cross-sectional imaging.

MR Spectroscopy Using Normalized and Non-normalized Metabolite Ratios for Differentiating Recurrent Brain Tumor from Radiation Injury

RATIONALE AND OBJECTIVES To compare the ability of normalized versus non-normalized metabolite ratios to differentiate recurrent brain tumor from radiation injury using magnetic resonance spectroscopy (MRS) in previously treated patients. MATERIALS AND METHODS Twenty-five patients with previous diagnosis of primary intracranial neoplasm confirmed with biopsy/resection, previously treated with radiation therapy (range, 54-70 Gy) with or without chemotherapy and new contrast enhancing lesion on a 1.5 T magnetic resonance imaging at the site of the primary neoplasm participated in this retrospective study. After MRS, clinical, radiological, and histopathology data were used to classify new contrast-enhancing lesions as either recurrent neoplasm or radiation injury. Volume of interest included both the lesion and normal-appearing brain on the contralateral side. Non-normalized metabolic ratios were calculated from choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) spectroscopic values obtained within the contrast-enhancing lesion: Cho/Cr, NAA/Cr, and Cho/NAA. Normalized ratios were calculated using the metabolic values from the contralateral normal side: Cho/normal creatinine (nCr), Cho/normal N-acetylaspartate (nNAA), Cho/normal choline, NAA/nNAA, NAA/nCr, and Cr/nCr. Results were correlated with the final diagnosis by Wilcoxon rank-sum analysis. RESULTS Two of three non-normalized ratios, Cho/NAA (sensitivity 86%, specificity 90%) and NAA/Cr (sensitivity 93%, specificity 70%) significantly associated with tumor recurrence even after correcting for multiple comparisons. Of the six normalized ratios, only Cho/nNAA significantly correlated with tumor recurrence (sensitivity 73%, specificity 40%), but did not remain significant after correcting for multiple comparisons. CONCLUSION Cho/NAA and NAA/Cr were the two ratios with the best discriminating ability and both had better discriminating ability than their corresponding normalized ratios (Area under the curve = 0.92 versus 0.77, AUC= 0.85 vs. 0.66), respectively.

Pediatric MR Enterography: Technique and Approach to Interpretation—How We Do It

Magnetic resonance (MR) enterography is an increasingly important pediatric imaging modality that is most often used to evaluate inflammatory bowel disease ( IBD inflammatory bowel disease ), while sparing children and adolescents from potential risks of ionizing radiation exposure. MR enterography allows for evaluation of the bowel lumen and wall, adjacent mesentery and soft tissues, as well as a variety of extraintestinal abdominopelvic IBD inflammatory bowel disease manifestations. While MR enterography can be used to initially confirm the diagnosis of IBD inflammatory bowel disease , particularly small bowel Crohn disease, it has also proven useful in assessing the degree inflammatory activity over time, serving as a radiologic biomarker for response to medical therapy, and identifying a variety of disease-related complications, including strictures, fistulae, and abscesses. The purpose of this review article is to provide radiologists with a systematic approach for MR enterography review and interpretation in children and adolescents with known or suspected of having IBD inflammatory bowel disease and to illustrate both common and infrequent but important imaging findings. Additionally, the authors will present their well-established and clinically successful pediatric MR enterography protocol, up-to-date clinical indications for MR enterography, and briefly mention the role of MR enterography in assessing non- IBD inflammatory bowel disease abnormalities affecting the bowel. Online supplemental material is available for this article .

MR Enterography of Extraluminal Manifestations of Inflammatory Bowel Disease in Children and Adolescents: Moving Beyond the Bowel Wall

OBJECTIVE The purpose of this review is to describe the extraintestinal manifestations of inflammatory bowel disease at MR enterography of children and adolescents. CONCLUSION MR enterography excellently depicts a variety of extraluminal manifestations of inflammatory bowel disease affecting a variety of organ systems. Because many of these findings can be clinically important, it is critical that radiologists look beyond the bowel wall when interpreting these images.

Equivocal Pediatric Appendicitis: Unenhanced MR Imaging Protocol for Nonsedated Children—A Clinical Effectiveness Study

PURPOSE To determine retrospectively the clinical effectiveness of an unenhanced magnetic resonance (MR) imaging protocol for evaluation of equivocal appendicitis in children. MATERIALS AND METHODS Institutional review board approval was obtained. Pediatric patients (≤18 years old) underwent unenhanced MR imaging and contrast material-enhanced computed tomography (CT) of the appendix between December 2013 and November 2014 and December 2012 and November 2013, respectively, within 24 hours after an abdominal ultrasonographic examination with results equivocal for appendicitis. Pertinent MR imaging and CT reports were reviewed for visibility of the appendix, presence of appendicitis and appendiceal perforation, and establishment of an alternative diagnosis. Surgical reports, pathologic reports, and 30-day follow-up medical records were used as reference standards. Diagnostic performance with MR imaging and CT was calculated with 95% confidence intervals (CIs) for diagnosis of appendicitis and appendiceal perforation. The Fisher exact test was used to compare proportions; the Student t test was used to compare means. RESULTS Diagnostic performance with MR imaging was comparable to that with CT for equivocal pediatric appendicitis. For MR imaging (n = 103), sensitivity was 94.4% (95% CI: 72.7%, 99.9%) and specificity was 100% (95% CI: 95.8%, 100%); for CT [n = 58], sensitivity was 100% (95% CI: 71.5%, 100%), specificity was 97.9% (95% CI: 88.7%, 100%). Diagnostic performance with MR imaging and CT also was comparable for detection of appendiceal perforation, with MR imaging (n = 103) sensitivity of 90.0% (95% CI: 55.5%, 99.8%) and specificity of 85.7% (95% CI: 42.1%, 99.6%) and CT (n = 58) sensitivity of 75.0% (95% CI: 19.4%, 99.4%) and specificity of 85.7% (95% CI: 42.1%, 99.6%). The proportion of examinations with identifiable alternative diagnoses was similar at MR imaging to that at CT (19 of 103 [18.4%] vs eight of 58 [13.8%], respectively; P = .52). The proportion of appendixes seen at MR imaging and at CT also was similar (77 of 103 [74.8%] vs 50 of 58 [86.2%], respectively; P = .11). CONCLUSION Unenhanced MR imaging is sensitive and specific for the diagnosis of equivocal appendicitis in nonsedated pediatric patients.

IV Glucagon Use in Pediatric MR Enterography: Effect on Image Quality, Length of Examination, and Patient Tolerance

OBJECTIVE The objective of our study was to evaluate the use of i.v. glucagon in pediatric patients undergoing MR enterography. SUBJECTS AND METHODS Forty-seven patients underwent clinical MR enterography examinations consisting of identical breath-hold T1-weighted 3D gradient-recalled echo fat-saturated pulse sequences before and after i.v. glucagon administration. Images were reviewed in a blinded manner by two pediatric radiologists to determine the effect of glucagon on visualization of the small and large bowel. Image time stamps were documented separately to determine how this adjunctive medication affected examination length. A separate cohort of 50 patients was evaluated for glucagon-related symptoms, including nausea and emesis. Exact binomial testing was performed to establish whether overall visualization of the bowel and visualization of the terminal ileum were better on images with i.v. glucagon. The two-tailed Wilcoxon signed rank test was used to compare Likertlike scores for bowel visualization before and after i.v. glucagon administration. RESULTS Glucagon improved overall bowel visualization in 40 of 47 (85%) examinations for reader 1 (p < 0.0001) and 36 of 47 (77%) for reader 2 (p = 0.0001). Visualization of the terminal ileum was improved after glucagon administration in 29 of 47 (62%) examinations for both readers (p = 0.03). Glucagon improved visualization of the small bowel for reader 1 (mean score on 5-point Likertlike scale: 3.3 ± 1.0 [SD] vs 2.2 ± 0.7, respectively; p < 0.0001) and reader 2 (3.4 ± 1.1 vs 2.5 ± 0.9; p < 0.0001). Glucagon also improved large-bowel visualization for reader 1 (3.3 ± 0.9 vs 3.0 ± 0.8; p = 0.005) and reader 2 (3.4 ± 1.1 vs 3.0 ± 1.0; p = 0.002). On average, the use of glucagon added 13.7 minutes to the examination. Twenty-four of 50 (48%) patients self-reported glucagon-related nausea and four patients experienced emesis. CONCLUSION I.v. glucagon improves bowel visualization at pediatric MR enterography, increases examination length, and commonly causes nausea. Fewer than 10% of patients experience glucagon-related emesis in our practice.

Vanishing fetal lung malformations: Prenatal sonographic characteristics and postnatal outcomes

BACKGROUND/PURPOSE The purpose of this study was to examine the natural history and outcomes of prenatally diagnosed lung masses that appear to undergo complete regression before birth. METHODS An IRB-approved retrospective review was performed on 100 consecutive fetuses with a congenital lung malformation at a single fetal center. Prenatal and postnatal imaging as well as outcomes of vanishing fetal masses was analyzed and compared to those with persistent fetal masses. RESULTS Seventeen lesions (17%) became sonographically undetectable at 35.3 ± 2.3 weeks gestation. Vanishing fetal masses were associated with microcystic disease (100% vs. 69%, p=0.005) and a low initial congenital pulmonary airway malformation volume ratio (CVR; 0.31 ± 0.35 vs. 0.70 ± 0.66, p=0.002) when compared to those with persistent fetal lesions. Based on postnatal CT imaging and pathology data, 10.3% of all fetal masses completely regressed. The positive predictive value and negative predictive value of prenatal ultrasound for detecting lung malformations in late gestation were 96% and 43%, respectively. All infants with vanishing fetal lesions were asymptomatic at birth and were more likely to be managed nonoperatively (75% vs. 22%, p<0.0001) when compared to infants with persistent fetal masses. CONCLUSIONS Vanishing lung lesions late in gestation are relatively common and are associated with a low CVR and microcystic disease.

Pediatric MR Urography: Indications, Techniques, and Approach to Review

Magnetic resonance (MR) urography is a valuable imaging modality for assessing disorders of the pediatric urinary tract. It allows comprehensive evaluation of the kidneys and urinary tract in children by providing both morphologic and functional information without exposing the child to ionizing radiation. Pediatric MR urography can be used to thoroughly evaluate renal and urinary tract abnormalities that are difficult to identify or fully characterize with other imaging techniques, and it has the potential to allow earlier diagnosis while decreasing the number of imaging studies performed. Common indications for pediatric MR urography include evaluation of complex renal and urinary tract anatomy, suspected urinary tract obstruction, operative planning, and postoperative assessment. MR hydrography (T2-weighted imaging of urine) excellently depicts dilated or obstructed urinary systems, whereas postcontrast imaging (gadolinium-enhanced T1-weighted imaging of the kidneys and urinary system) excellently depicts nondilated or nonobstructed urinary systems. Postcontrast MR urography also allows a functional evaluation of the kidneys and urinary tract that includes estimation of differential renal function. The authors review common indications for pediatric MR urography, detail MR urography techniques, compare the strengths and weaknesses of MR urography with those of alternative imaging strategies for children, and describe numerous common and uncommon abnormalities of the pediatric kidneys and urinary tract.