Maria-Helena Smet

The value of fast MR imaging as an adjunct to ultrasound in prenatal diagnosis

Abstract.The aim of this study was to evaluate the role of MR imaging of the fetus to improve sonographic prenatal diagnosis of congenital anomalies. In 40 fetuses (not consecutive cases) with an abnormality diagnosed with ultrasound, additional MR imaging was performed. The basic sequence was a T2-weighted single-shot half Fourier (HASTE) technique. Head, neck, spinal, thoracic, urogenital, and abdominal fetal pathologies were found. This retrospective, observational study compared MR imaging findings with ultrasonographic findings regarding detection, topography, and etiology of the pathology. The MR findings were evaluated as superior, equal to, or inferior compared with US, in consent with the referring gynecologists. The role of these findings in relation to pregnancy management was studied and compared with postnatal follow-up in 30 of 40 babies. Fetal MRI technique was successful in 36 of 39 examinations and provided additional information in 21 of 40 fetuses (one twin pregnancy with two members to evaluate). More precise anatomy and location of fetal pathology (20 of 40 cases) and additional etiologic information (8 of 40 cases) were substantial advantages in cerebrospinal abnormalities [ventriculomegaly, encephalocele, vein of Galen malformation, callosal malformations, meningo(myelo)cele], in retroperitoneal abnormalities (lymphangioma, renal agenesis, multicystic renal dysplasia), and in neck/thoracic pathology [cervical cystic teratoma, congenital hernia diaphragmatica, congenital cystic adenomatoid lung malformation (CCAM)]. This improved parental counseling and pregnancy management in 15 pregnancies. In 3 cases, prenatal MRI findings did not correlate with prenatal ultrasonographic findings or neonatal diagnosis. The MRI provided a more detailed description and insight into fetal anatomy, pathology, and etiology in the vast majority of these selected cases. This improved prenatal parental counseling and postnatal therapeutic planning.

Three-Dimensional Computed Tomography-Based, Personalized Drill Guide for Posterior Cervical Stabilization at C1-C2

Study Design. Cadaver and preliminary clinical study. Objectives. To enhance the precision of screw positions for posterior transarticular fixations according to Magerl at C1–C2. Summary of Background Data. The vertebral arteries are at risk during the Magerl operation and may be damaged in up to 4.1% of cases. Even intraoperative navigation, as often used nowadays, does not provide optimal screw positioning in all patients. Methods. According to the three-dimensional CT data obtained for every individual cadaver or patient, a template was designed for the posterior course of C2: the template contains a drill guide allowing navigated screw positioning inside the left and right isthmus of C2. For a first series of five cadavers a template with clamps connecting only to the lamina of C2, excluding the spinous process from the interface, was carried out. For a second series of three cadavers the template was connected not only to the lamina but also to the spinous process of C2. Both cadaver series were performed without any fluoroscopic control at surgery. Eventually the technology was applied in two clinical cases. Results. The rotational stability of the template toward the lamina C2 was insufficient in the first series, but for the second series both the entry points and screw trajectories were very satisfactory . Conclusions. Although the actual experience is limited, the idea of using a template with drill guide might simplify and shorten the surgical act and at the same time enhance the accuracy of C1–C2 transarticular screw positioning.

A Novel Method for the Nonradiological Assessment of Ineffective Swallowing

OBJECTIVES:This validation study evaluates a new manometry impedance-based approach for the objective assessment of pharyngeal function relevant to postswallow bolus residue.METHODS:We studied 23 adult and pediatric dysphagic patients who were all referred for a videofluoroscopy, and compared these patients with 10 adult controls. The pharyngeal phase of swallowing of semisolid boluses was recorded with manometry and impedance. Fluoroscopic evidence of postswallow bolus residue was scored. Pharyngeal pressure impedance profiles were analyzed. Computational algorithms measured peak pressure (Peak P), pressure at nadir impedance (PNadImp), time from nadir impedance to PeakP (PNadImp–PeakP), the duration of impedance drop in the distal pharynx (flow interval), upper esophaghageal sphincter (UES) relaxation interval (UES-RI), nadir UES pressure (NadUESP), UES intrabolus pressure (UES-IBP), and UES resistance. A swallow risk index (SRI) was derived by the formula: SRI=(FI × PNadImp)/(PeakP × (TNadImp-PeakP+1)) × 100.RESULTS:In all, 76 patient swallows (35 with residue) and 39 control swallows (12 with residue) were analyzed. Different functional variables were found to be altered in relation to residue. In both controls and patients, flow interval was longer in relation to residue. In controls, but not patients, residue was associated with an increased PNadImp (suggestive of increased pharyngeal IBP). Controls with residue had increased UES-IBP, NadUESP, and UES resistance compared with patients with residue. Residue in patients was related to a prolonged UES-RI. The SRI was elevated in relation to residue in both controls and patients and an average SRI of 9 was optimally predictive of residue (sensitivity 75% and specificity 80%).CONCLUSIONS:We present novel findings in control subjects and dysphagic patients showing that combined manometry and impedance recordings can be objectively analyzed to derive pressure-flow variables that are altered in relation to the bolus residual and can be combined to predict ineffective pharyngeal swallowing.

Image segmentation: methods and applications in diagnostic radiology and nuclear medicine

We review and discuss different classes of image segmentation methods. The usefulness of these methods is illustrated by a number of clinical cases. Segmentation is the process of assigning labels to pixels in 2D images or voxels in 3D images. Typically the effect is that the image is split up into segments, also called regions or areas. In medical imaging it is essential for quantification of outlined structures and for 3D visualization of relevant image data. Based on the level of implemented model knowledge we have classified these methods into (1) manual delineation, (2) low-level segmentation, and (3) model-based segmentation. Pure manual delineation of structures in a series of images is time-consuming and user-dependent and should therefore be restricted to quick experiments. Low-level segmentation analyzes the image locally at each pixel in the image and is practically limited to high-contrast images. Model-based segmentation uses knowledge of object structure such as global shape or semantic context. It typically requires an initialization, for example in the form of a rough approximation of the contour to be found. In practice it turns out that the use of high-level knowledge, e.g. anatomical knowledge, in the segmentation algorithm is quite complicated. Generally, the number of clinical applications decreases with the level and extent of prior knowledge needed by the segmentation algorithm. Most problems of segmentation inaccuracies can be overcome by human interaction. Promising segmentation methods for complex images are therefore user-guided and thus semi-automatic. They require manual intervention and guidance and consist of fast and accurate refinement techniques to assist the human operator.

Sonographic demonstration of congenital adrenal hyperplasia in the neonate: The cerebriform pattern

Sonographic examination of the adrenal glands of three newborns with congenital adrenal hyperplasia demonstrated a cerebriform pattern. This is introduced as a sonographic feature specific to the disease. This finding in patients with ambiguous genitalia should suggest the diagnosis even if the adrenals are not significantly enlarged, and should prompt appropriate biochemical analysis and treatment.

Rickets due to dietary calcium deficiency.

Three children, aged 15–18 months were referred because of clinical, radiological and biochemical manifestations of rickets. Serum 25-hydroxycholecalciferol (25-OH-D3) values were within the normal range but 1,25-dihydroxychole-calciferol (1,25-diOH-D3) levels were markedly elevated. All signs and symptoms could be explained by dietary calcium deficiency. They all received the commercial Soya-drink — not adapted for infants — as their main source of nutrition for at least 6 months. Soya-drink has as extremely low calcium content. It should be remembered that defective calcium intake causes severe bone lesions and rickets in children in spite of adequate vitamin D supply.

Cross-sectional study of tracheomegaly in children after fetal tracheal occlusion for severe congenital diaphragmatic hernia

PURPOSE To measure tracheal dimensions in children with congenital diaphragmatic hernia (CDH) who had undergone fetoscopic endoluminal tracheal occlusion (FETO) or were treated expectantly during gestation. MATERIALS AND METHODS The study was approved by the local ethics committee. Computed tomography was performed in 23 patients (14 boys and nine girls) aged 1 month to 6.5 years, and the anteroposterior diameter, width, area, and perimeter of the trachea were determined. Seven of the 23 patients had undergone FETO and 16 had been treated expectantly. The relative difference of each parameter between the two most proximal concentric sections of the trachea, just below the larynx, and the two sections on which the trachea was the largest was compared between both groups (Mann-Whitney U test). Regression statistics were applied to maximum and mean tracheal areas as a function of age. Each trachea was divided into quartiles, and mean areas normalized to 3 years of age were analyzed for each quartile as a function of its relative position on the trachea (Student t test). RESULTS Tracheal width, area, and perimeter were significantly different between both groups. A linear relationship was observed between the maximum and mean tracheal areas and age for both the FETO group (maximum tracheal area: R(2) = 0.83, P = .0045; mean tracheal area: R(2) = 0.92, P = .0005) and the non-FETO group (maximum tracheal area: R(2) = 0.66, P = .0001; mean trachea area: R(2) = 0.66, P = .0001). The maximum tracheal area in both groups tended to decrease toward the age of 5 years. Significantly different mean tracheal areas per tracheal quartile (P < .05) were found for all quartiles except for the proximal one-fourth. CONCLUSION The relative difference between proximal and largest tracheal width, area, and perimeter was significantly larger in patients who underwent FETO than in those treated expectantly, demonstrating tracheal dilatation in the former. Measurements of tracheal dimensions at different levels indicate a maximum dilatation in the lower half of the trachea, which tends to level off toward the age of 5 years.

Fetal trauma: brain imaging in four neonates

The purpose of this paper is to describe brain pathology in neonates after major traffic trauma in utero during the third trimester. Our patient cohort consisted of four neonates born by emergency cesarean section after car accident in the third trimester of pregnancy. The median gestational age (n=4) was 36 weeks (range: 30–38). Immediate post-natal and follow-up brain imaging consisted of cranial ultrasound (n=4), computed tomography (CT) (n=1) and post-mortem magnetic resonance imaging (MRI) (n=1). Pathology findings were correlated with the imaging findings (n=3). Cranial ultrasound demonstrated a huge subarachnoidal hemorrhage (n=1), subdural hematoma (n=1), brain edema with inversion of the diastolic flow (n=1) and severe ischemic changes (n=1). In one case, CT demonstrated the presence and extension of the subarachnoidal hemorrhage, a parietal fracture and a limited intraventricular hemorrhage. Cerebellar hemorrhage and a small cerebral frontal contusion were seen on post-mortem MRI in a child with a major subarachnoidal hemorrhage on ultrasound. None of these four children survived (three children died within 2 days and one child died after 1 month). Blunt abdominal trauma during pregnancy can cause fetal cranial injury. In our cases, skull fracture, intracranial hemorrhage and hypoxic-ischemic encephalopathy were encountered.

Patient dose in neonatal units.

Lung disease represents one of the most life-threatening conditions in prematurely born children. In the evaluation of the neonatal chest, the primary and most important diagnostic study is therefore the chest radiograph. Since prematurely born children are very sensitive to radiation, those radiographs may lead to a significant radiation detriment. Hence, knowledge of the patient dose is necessary to justify the exposures. A study to assess the patient doses was started at the neonatal intensive care unit (NICU) of the University Hospital in Leuven. Between September 2004 and September 2005, prematurely born babies underwent on average 10 X-ray examinations in the NICU. In this sample, the maximum was 78 X-ray examinations. For chest radiographs, the median entrance skin dose was 34 microGy and the median dose area product was 7.1 mGy.cm(2). By means of conversion coefficients, the measured values were converted to organ doses. Organ doses were calculated for three different weight classes: extremely low birth weight infants (<1000 g), low birth weight infants (1000-2500 g) and normal birth weight infants (>2500 g). The doses to the lungs for a single chest radiograph for infants with extremely low birth weights, low birth weights and normal birth weights were 24, 25 and 32 microGy, respectively.

Calculation of organ doses in x-ray examinations of premature babies

Lung disease represents one of the most life-threatening conditions in prematurely born children. In the evaluation of the neonatal chest, the primary and most important diagnostic study is the chest radiograph. Since prematurely born children are very sensitive to radiation, those radiographs may lead to a significant radiation detriment. Knowledge of the radiation dose is therefore necessary to justify the exposures. To calculate doses in the entire body and in specific organs, computational models of the human anatomy are needed. Using medical imaging techniques, voxel phantoms have been developed to achieve a representation as close as possible to the anatomical properties. In this study two voxel phantoms, representing prematurely born babies, were created from computed tomography- and magnetic resonance images: Phantom 1 (1910 g) and Phantom 2 (590 g). The two voxel phantoms were used in Monte Carlo calculations (MCNPX) to assess organ doses. The results were compared with the commercially available software package PCXMC in which the available mathematical phantoms can be downsized toward the prematurely born baby. The simple phantom-scaling method used in PCXMC seems to be sufficient to calculate doses for organs within the radiation field. However, one should be careful in specifying the irradiation geometry. Doses in organs that are wholly or partially outside the primary radiation field depend critically on the irradiation conditions and the phantom model.