Choon Sik Yoon

Scoliosis Imaging: What Radiologists Should Know

Scoliosis is defined as a lateral spinal curvature with a Cobb angle of 10° or more. This abnormal curvature may be the result of an underlying congenital or developmental osseous or neurologic abnormality, but in most cases the cause is unknown. Imaging modalities such as radiography, computed tomography (CT), and magnetic resonance (MR) imaging play pivotal roles in the diagnosis, monitoring, and management of scoliosis, with radiography having the primary role and with MR imaging or CT indicated when the presence of an underlying osseous or neurologic cause is suspected. In interpreting the imaging features of scoliosis, it is essential to identify the significance of vertebrae in or near the curved segment (apex, end vertebra, neutral vertebra, stable vertebra), the curve type (primary or secondary, structural or nonstructural), the degree of angulation (measured with the Cobb method), the degree of vertebral rotation (measured with the Nash-Moe method), and the longitudinal extent of spinal involvement (according to the Lenke system). The treatment of idiopathic scoliosis is governed by the severity of the initial curvature and the probability of progression. When planning treatment or follow-up imaging, the biomechanics of curve progression must be considered: In idiopathic scoliosis, progression is most likely during periods of rapid growth, and the optimal follow-up interval in skeletally immature patients may be as short as 4 months. After skeletal maturity is attained, only curves of more than 30° must be monitored for progression.

Biliary Atresia: Color Doppler US Findings in Neonates and Infants

PURPOSE To describe color Doppler ultrasonographic (US) findings in livers of neonates with biliary atresia (BA) and to compare them with US findings in livers of neonates with non-BA and control subjects. MATERIALS AND METHODS Institutional review board approval was obtained; acquisition of informed consent was exempted. US and color Doppler US findings were retrospectively reviewed in 64 patients with neonatal cholestasis and 19 control subjects. BA and non-BA were confirmed in 29 and 35 patients, respectively. Three pediatric radiologists assessed US and color Doppler US images, independently documented their findings, and resolved discrepancies by consensus. Triangular cord (TC) sign, gallbladder length, and hepatic artery and portal vein diameters were evaluated on US images. The presence of hepatic subcapsular flow was evaluated on color Doppler US images. Diagnostic value of TC sign and hepatic subcapsular flow in the diagnosis of BA were evaluated. Significance of hepatic artery and portal vein diameters in each group was assessed. RESULTS In the diagnosis of BA, sensitivity and specificity of the TC sign on US images were 62% and 100%, respectively. On color Doppler US images, hepatic subcapsular flow was detected in all patients with BA and in five patients with non-BA. At the first review, there was a discrepancy between radiologists in interpretation of hepatic subcapsular flow in patients with non-BA. However, consensus was reached at the second review. There was no hepatic subcapsular flow in control subjects. Sensitivity and specificity of hepatic subcapsular flow on color Doppler US images were 100% and 80%-86%, respectively, on the basis of individual interpretations of reviewers. Sensitivity and specificity of hepatic subcapsular flow on color Doppler US images were 100% and 86%, respectively, on the basis of consensus reading. Mean diameter of the hepatic artery in patients with BA (2.1 mm +/- 0.7 [standard deviation]) was significantly larger than that in patients with non-BA (1.5 mm +/- 0.4, P < .001) and control subjects (1.5 mm +/- 0.4, P = .001). CONCLUSION The presence of hepatic subcapsular flow is useful for differentiating between BA and other causes of neonatal jaundice.

Age-related changes in liver, kidney, and spleen stiffness in healthy children measured with acoustic radiation force impulse imaging

OBJECTIVES To evaluate the feasibility and age-related changes of shear wave velocity (SWV) in normal livers, kidneys, and spleens of children using acoustic radiation force impulse (ARFI) imaging. MATERIALS AND METHODS Healthy pediatric volunteers prospectively underwent abdominal ultrasonography and ARFI. The subjects were divided into three groups according to age: group 1: <5 years old; group 2: 5-10 years old; and group 3: >10 years old. The SWV was measured using a 4-9 MHz linear probe for group 1 and a 1-4 MHz convex probe for groups 2 and 3. Three valid SWV measurements were acquired for each organ. RESULTS Two hundred and two children (92 male, 110 female) with an average age of 8.1 years (± 4.7) were included in this study and had a successful measurement rate of 97% (196/202). The mean SWVs were 1.12 m/s for the liver, 2.19 m/s for the right kidney, 2.33 m/s for the left kidney, and 2.25 m/s for the spleen. The SWVs for the right and left kidneys, and the spleen showed age-related changes in all children (p<0.001). And the SWVs for the kidneys increased with age in group 1, and those for the liver changed with age in group 3. CONCLUSIONS ARFI measurements are feasible for solid abdominal organs in children using high or low frequency probes. The mean ARFI SWV for the kidneys increased according to age in children less than 5 years of age and in the liver, it changed with age in children over 10.

Comparison of Multi-Echo Dixon Methods with Volume Interpolated Breath-Hold Gradient Echo Magnetic Resonance Imaging in Fat-Signal Fraction Quantification of Paravertebral Muscle.

Objective To assess whether multi-echo Dixon magnetic resonance (MR) imaging with simultaneous T2* estimation and correction yields more accurate fat-signal fraction (FF) measurement of the lumbar paravertebral muscles, in comparison with non-T2*-corrected two-echo Dixon or T2*-corrected three-echo Dixon, using the FF measurements from single-voxel MR spectroscopy as the reference standard. Materials and Methods Sixty patients with low back pain underwent MR imaging with a 1.5T scanner. FF mapping images automatically obtained using T2*-corrected Dixon technique with two (non-T2*-corrected), three, and six echoes, were compared with images from single-voxel MR spectroscopy at the paravertebral muscles on levels L4 through L5. FFs were measured directly by two radiologists, who independently drew the region of interest on the mapping images from the three sequences. Results A total of 117 spectroscopic measurements were performed either bilaterally (57 of 60 subjects) or unilaterally (3 of 60 subjects). The mean spectroscopic FF was 14.3 ± 11.7% (range, 1.9-63.7%). Interobserver agreement was excellent between the two radiologists. Lins concordance correlation between the spectroscopic findings and all the imaging-based FFs were statistically significant (p < 0.001). FFs obtained from the T2*-corrected six-echo Dixon sequences showed a significantly better concordance with the spectroscopic data, with its concordance correlation coefficient being 0.99 and 0.98 (p < 0.001), as compared with two- or three-echo methods. Conclusion T2*-corrected six-echo Dixon sequence would be a better option than two- or three-echo methods for noninvasive quantification of lumbar muscle fat quantification.

A Case of Suspected Isotretinoin-Induced Malformation in a Baby of a Mother Who Became Pregnant One Month after Discontinuation of the Drug

Isotretinoin is a known human teratogen that can cause multiple malformations. At present, women who conceive one cycle after discontinuing isotretinoin are told that their teratogenic risk is not higher than baseline. We present a case of both ear malformation in a newborn whose mother had taken isotretinoin for 2 years until one month prior to the time when she became pregnant. We suggest that further studies of pharmacokinetics and malformation of isotreinoin are needed.

Differentiation between focal malignant marrow-replacing lesions and benign red marrow deposition of the spine with T2*-corrected fat-signal fraction map using a three-echo volume interpolated breath-hold gradient echo Dixon sequence.

Objective To assess the feasibility of T2*-corrected fat-signal fraction (FF) map by using the three-echo volume interpolated breath-hold gradient echo (VIBE) Dixon sequence to differentiate between malignant marrow-replacing lesions and benign red marrow deposition of vertebrae. Materials and Methods We assessed 32 lesions from 32 patients who underwent magnetic resonance imaging after being referred for assessment of a known or possible vertebral marrow abnormality. The lesions were divided into 21 malignant marrow-replacing lesions and 11 benign red marrow depositions. Three sequences for the parameter measurements were obtained by using a 1.5-T MR imaging scanner as follows: three-echo VIBE Dixon sequence for FF; conventional T1-weighted imaging for the lesion-disc ratio (LDR); pre- and post-gadolinium enhanced fat-suppressed T1-weighted images for the contrast-enhancement ratio (CER). A region of interest was drawn for each lesion for parameter measurements. The areas under the curve (AUC) of the parameters and their sensitivities and specificities at the most ideal cutoff values from receiver operating characteristic curve analysis were obtained. AUC, sensitivity, and specificity were respectively compared between FF and CER. Results The AUCs of FF, LDR, and CER were 0.96, 0.80, and 0.72, respectively. In the comparison of diagnostic performance between the FF and CER, the FF showed a significantly larger AUC as compared to the CER (p = 0.030), although the difference of sensitivity (p = 0.157) and specificity (p = 0.157) were not significant. Conclusion Fat-signal fraction measurement using T2*-corrected three-echo VIBE Dixon sequence is feasible and has a more accurate diagnostic performance, than the CER, in distinguishing benign red marrow deposition from malignant bone marrow-replacing lesions.

Accuracy of diffusion tensor imaging for diagnosing cervical spondylotic myelopathy in patients showing spinal cord compression

Objective To assess the performance of diffusion tensor imaging (DTI) for the diagnosis of cervical spondylotic myelopathy (CSM) in patients with deformed spinal cord but otherwise unremarkable conventional magnetic resonance imaging (MRI) findings. Materials and Methods A total of 33 patients who underwent MRI of the cervical spine including DTI using two-dimensional single-shot interleaved multi-section inner volume diffusion-weighted echo-planar imaging and whose spinal cords were deformed but showed no signal changes on conventional MRI were the subjects of this study. Mean diffusivity (MD), longitudinal diffusivity (LD), radial diffusivity (RD), and fractional anisotropy (FA) were measured at the most stenotic level. The calculated performance of MD, FA, MD∩FA (considered positive when both the MD and FA results were positive), LD∩FA (considered positive when both the LD and FA results were positive), and RD∩FA (considered positive when both the RD and FA results were positive) in diagnosing CSM were compared with each other based on the estimated cut-off values of MD, LD, RD, and FA from receiver operating characteristic curve analysis with the clinical diagnosis of CSM from medical records as the reference standard. Results The MD, LD, and RD cut-off values were 1.079 × 10-3, 1.719 × 10-3, and 0.749 × 10-3 mm2/sec, respectively, and that of FA was 0.475. Sensitivity, specificity, positive predictive value and negative predictive value were: 100 (4/4), 44.8 (13/29), 20 (4/20), and 100 (13/13) for MD; 100 (4/4), 27.6 (8/29), 16 (4/25), and 100 (8/8) for FA; 100 (4/4), 58.6 (17/29), 25 (4/16), and 100 (17/17) for MD∩FA; 100 (4/4), 68.9 (20/29), 30.8 (4/13), and 100 (20/20) for LD∩FA; and 75 (3/4), 68.9 (20/29), 25 (3/12), and 95.2 (20/21) for RD∩FA in percentage value. Diagnostic performance comparisons revealed significant differences only in specificity between FA and MD∩FA (p = 0.003), FA and LD∩FA (p < 0.001), FA and RD∩FA (p < 0.001), MD and LD∩FA (p = 0.024) and MD and RD∩FA (p = 0.024). Conclusion Fractional anisotropy combined with MD, RD, or LD is expected to be more useful than FA and MD for diagnosing CSM in patients who show deformed spinal cords without signal changes on MRI.

The T2-Shortening Effect of Gadolinium and the Optimal Conditions for Maximizing the CNR for Evaluating the Biliary System: a Phantom Study

Objective Clear depiction of the common bile duct is important when evaluating neonatal cholestasis in order to differentiate biliary atresia from other diseases. During MR cholangiopancreatography, the T2-shortening effect of gadolinium can increase the contrast-to-noise ratio (CNR) of the bile duct and enhance its depiction. The purpose of this study was to confirm, by performing a phantom study, the T2-shortening effect of gadolinium, to evaluate the effect of different gadolinium chelates with different gadolinium concentrations and different magnetic field strengths for investigating the optimal combination of these conditions, and for identifying the maximum CNR for the evaluation of the biliary system. Materials and Methods MR imaging using a T2-weighted single-shot fast spin echo sequence and T2 relaxometry was performed with a sponge phantom in a syringe tube. Two kinds of contrast agents (Gd-DTPA and Gd-EOB-DTPA) with different gadolinium concentrations were evaluated with 1.5T and 3T scanners. The signal intensities, the CNRs and the T2 relaxation time were analyzed. Results The signal intensities significantly decreased as the gadolinium concentrations increased (p < 0.001) with both contrast agents. These signal intensities were higher on a 3T (p < 0.001) scanner. The CNRs were higher on a 1.5T (p < 0.001) scanner and they showed no significant change with different gadolinium concentrations. The T2 relaxation time also showed a negative correlation with the gadolinium concentrations (p < 0.001) and the CNRs showed decrease more with Gd-EOB-DTPA (versus Gd-DTPA; p < 0.001) on a 3T scanner (versus 1.5T; p < 0.001). Conclusion A T2-shortening effect of gadolinium exhibits a negative correlation with the gadolinium concentration for both the signal intensities and the T2 relaxation time. A higher CNR can be obtained with Gd-DTPA on a 1.5T MRI scanner.

The First Korean Case of Camurati-Engelmann Disease (Progressive Diaphyseal Dysplasia) Confirmed by TGFB1 Gene Mutation Analysis

Camurati-Engelmann disease (CED) is an autosomal dominant progressive diaphyseal dysplasia caused by mutations in the transforming growth factor-β1 (TGFB1) gene. We report the first Korean family with an affected mother and son who were diagnosed with CED. The proband is a 19-yr-old male with a history of abnormal gait since the age of 2. He also suffered from proximal muscle weakness, pain in the extremities, and easy fatigability. Skeletal radiographs of the long bones revealed cortical, periosteal, and endosteal thickenings, predominantly affecting the diaphyses of the upper and lower extremities. No other bony abnormalities were noted in the skull and spine and no remarkable findings were seen on laboratory tests. The patients mother had a long-standing history of mild limb pain. Under the impression of CED on radiographic studies, we performed mutation analysis. A heterozygous G to A transition at cDNA position +653 in exon 4 of the TGFB1 gene (R218H) was detected in the patient and his mother.

Ultrasound measurement of pediatric visceral fat thickness: correlations with metabolic and liver profiles

Purpose Abdominal obesity is a fundamental factor underlying the development of metabolic syndrome. Because of radiation exposure and cost, computed tomography or dual-energy X-ray absorptiometry to evaluate abdominal adiposity are not appropriate in children. Authors evaluated whether ultrasound results could be an indicator of insulin resistance and nonalcoholic fatty liver disease (NAFLD). Methods We enrolled 73 subjects (aged 6–16 years) who were evaluated abdominal adiposity by ultrasound. Subcutaneous fat thickness was defined as the measurement from the skin-fat interface to the linea alba, and visceral fat thickness (VFT) was defined as the thickness from the linea alba to the aorta. Anthropometric and biochemical metabolic parameters were also collected and compared. The subjects who met 2 criteria, radiologic confirmed fatty liver and alanine aminotransferase >40, were diagnosed with NAFLD. Results There was a strong positive correlation between VFT and obesity. VFT was highly correlated with the homeostasis model assessment for insulin resistance score (r=0.403, P<0.001). The area under the curve for VFT as a predictor of NAFLD was 0.875 (95% confidence interval [CI], 0.787–0.964). VFT of 34.3 mm was found to be the discriminating cutoff for NAFLD (sensitivity, 84.6%; specificity, 71.2%, respectively). Conclusion Ultrasound could be useful in measuring VFT and assessing abdominal adiposity in children. Moreover, increased VFT might be an appropriate prognostic factor for insulin resistance and NAFLD.