Evaluation of image registration in subtracted 3D dynamic contrast-enhanced MRI of treated hepatocellular carcinoma.

OBJECTIVE. The objective of our study was to quantify hepatic displacement between breath-holds in multiphasic contrast-enhanced MRI and assess the value of a 3D registration algorithm for displacement correction on subtracted images. MATERIALS AND METHODS. For this retrospective analysis, we evaluated MR images of 25 cirrhotic patients with treated hepatocellular carcinoma (HCC) and at least one coexisting small hepatic cyst that was hypointense on T1-weighted imaging. With the use of an automated 3D deformable registration algorithm, registered base and subtraction images were created using portal venous phase images as the baseline images. The relative displacement of the cysts over the dynamic phases was used to estimate hepatic displacement before and after registration. The width of the subtraction band artifact, HCC lesion conspicuity, and overall subtraction artifact level (i.e., image quality of the entire volume) of the subtraction images were evaluated before and after registration on a 5-point scale (1 = nondiagnostic, 5 = excellent image quality) by two blinded radiologists. Hepatic displacement and subtraction band artifact results were analyzed using the paired Student t test, and the results for HCC lesion conspicuity and image quality of the volume results were analyzed using the Wilcoxon signed rank test. Interobserver agreement was assessed using kappa statistics. RESULTS. The average total cyst displacement on unenhanced, arterial, and delayed phase images was significantly reduced by registration from 4.0, 3.2, and 4.6 mm, respectively, on pre-registered images to 2.4, 1.6, and 1.3 mm on postregistered images (p < 0.01). The mean HCC lesion conspicuity grade improved from 3.4 before registration to 4.4 after registration (p < 0.01), and the mean grade for image quality of the volume improved from 3.3 before registration to 4.6 after registration (p < 0.01). The average width of the subtraction band artifact decreased from 5.3 mm before registration to 2.4 mm after registration, from 6.1 mm before registration to 2.6 mm after registration, and from 5.2 mm before registration to 2.8 mm after registration for the arterial, portal venous, and delayed phase subtractions, respectively (p < 0.01). CONCLUSION. Automated registration of the liver in multiphasic MRI examinations reduced interphasic hepatic displacement, improved the conspicuity of the treated HCC lesion, and improved the overall subtraction image quality.

ASER Core Curriculum Illustration Project: coronal femoral condyle (Hoffa) fracture.

This is the 13th installment of a series that will highlight one case per publication issue from the bank of cases available online as part of the American Society of Emergency Radiology (ASER) educational resources. Our goal is to generate more interest in and use of our online materials. To view more cases online, please visit the ASER Core Curriculum and Recommendations for study online at http://www.aseronline.org/curriculum/toc.htm.

Comprehensive imaging review of abnormalities of the umbilical cord.

A complete fetal ultrasonographic (US) study includes assessment of the umbilical cord for possible abnormalities. Knowledge of the normal appearance of the umbilical cord is necessary for the radiologist to correctly diagnose pathologic conditions. Umbilical cord abnormalities can be related to cord coiling, length, and thickness; the placental insertion site; in utero distortion; vascular abnormalities; and primary tumors or masses. These conditions may be associated with other fetal anomalies and aneuploidies, and their discovery should prompt a thorough fetal US examination. Further workup and planning for a safe fetal delivery may include fetal echocardiography and karyotype analysis. Doppler US is a critical tool for assessment and diagnosis of vascular cord abnormalities. US also can be used for follow-up serial imaging evaluation of conditions that could result in fetal demise. Recent studies suggest that three- or four-dimensional Doppler US of the fetal umbilical cord and abdominal vasculature allows more accurate diagnosis of vascular abnormalities. Doppler US also is invaluable in assessment of fetal growth restriction since hemodynamic changes in the placenta or fetus would appear as a spectral pattern of increased resistance to forward flow in the fetal umbilical artery. Early detection of umbilical cord abnormalities and close follow-up can reduce the risk of morbidity and mortality and assist in decision making.

Core curriculum illustration: testicular torsion.

This is the 7th installment of a series that will highlight one case per publication issue from the bank of cases available online as part of the American Society of Emergency Radiology (ASER) educational resources. Our goal is to generate more interest in and use of our online materials. To view more cases online, please visit the ASER Core Curriculum and Recommendations for Study online at http://www.aseronline.org/curriculum/toc.htm .

Comprehensive Imaging Review of Abnormalities of the Placenta.

The placenta has a fundamental role in fetal health and functions as an important bridge to normal fetal development throughout pregnancy. A complete fetal ultrasound (US) survey should include full assessment of the placenta for any possible abnormalities. Placental diseases range from abnormal morphology, size, location, extent, and degree of placentation, to abruption and the presence of rare placental neoplasms of benign or malignant nature. Some of these conditions are associated with other diseases including aneuploidies, and their discovery should alert the radiologist to perform a very thorough fetal US examination. At times, a fetal karyotype may be needed to provide additional information. Timely detection of placental abnormalities can alert the clinician regarding the need to make important management decisions to reduce fetal and maternal morbidity and mortality. Familiarity with the normal and abnormal imaging appearance of the placenta is therefore necessary for the radiologist. Ultrasound with Doppler is the initial imaging modality of choice for placental assessment. Magnetic resonance imaging serves as a problem-solving examination in instances where the US findings are equivocal or where additional information is needed. Computed tomography has a limited role in the evaluation of placental disease because of its relatively limited tissue characterization and in particular because of the resultant direct radiation exposure of the fetus. However, in specific instances, particularly after trauma, computed tomography can provide invaluable information for patient management.