Sonography of the normal ulnar nerve at Guyon's canal and of the common peroneal nerve dorsal to the fibular head.

PURPOSE: This study was conducted to evaluate the ability of sonography to visualize the ulnar nerve at Guyon's canal and the common peroneal nerve dorsal to the fibular head and to test for correlations between nerve measurements and subject characteristics. METHODS: We used a 5-12-MHz linear-array transducer in sonographic evaluation of 15 healthy adult volunteers. We evaluated the correlations between nerve diameters and surface areas and subject body mass index and height. We also tested for differences between nerve measurements in women and men and between nerve measurements from the left and right sides of the body. RESULTS: Both nerves were visualized in all subjects. Subject height correlated significantly with the anteroposterior diameter of the right ulnar nerve. Body mass index correlated significantly with the surface area of both ulnar nerves, with the anteroposterior diameter of both ulnar nerves, with the transverse diameter of the left ulnar nerve, and with the transverse diameter of the right common peroneal nerve. There was a statistically significant difference in anteroposterior diameter of the left ulnar and left common peroneal nerves between women and men. There were no significant differences between left- and right-side measurements for the combined data from the entire group of subjects. CONCLUSIONS: A 5-12-MHz linear-array transducer readily allows for visualization of the ulnar nerve at Guyon's canal and the common peroneal nerve dorsal to the fibular head.

Deconvolution of dynamic contrast-enhanced MRI data by linear inversion: choice of the regularization parameter.

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast-enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel-by-pixel basis--generalized cross validation (GCV) and the L-curve criterion (LCC)--were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1-2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster.

Normal osseous variants presenting as cystic or lucent areas on radiography and CT imaging: a pictorial overview.

We present a number of commonly encountered pseudolesions. These represent areas of the skeleton that are relatively radiolucent simulating an osteolytic or cystic lesion. Such areas discussed in this article include the superolateral humeral head, rhomboid fossa of the clavicle, scapular defect, supratrochlear foramen, biceps tendon insertion, vascular channel of the ulna, distal condylar area of the knee, 'bone in bone' disturbance, dorsal defect of the patella, metadiaphyseal area, 'Wards' triangle', inframalleolar fossa of the fibula, and anterior lytic defect of the calcaneus. We provide an overview of commonly encountered pseudolesions, that may lead to false positive diagnosis of an osteolytic or cystic lesion.

Evaluation of patient and staff doses during various CT fluoroscopy guided interventions.

As CT scanners are more routinely used as a guidance tool for various types of interventional radiological procedures, concern has grown for high patient and staff doses. CT fluoroscopy provides the physician immediate feedback and can be a valuable tool to dynamically assist various types of percutaneous interventions. However, the fixed position of the scanning plane in combination with high exposure factors may lead to high cumulative patient skin doses that can reach deterministic threshold limits. The staff is also exposed to a considerable amount of scatter radiation while standing next to the patient during the procedures. Although some studies have been published dealing with this subject, data of patient skin doses determined by direct in vivo dosimetry remains scarce. The purpose of this study is to quantify and to evaluate both patient and staff doses by direct thermoluminescent dosimetry during various clinical CT fluoroscopy guided procedures. Patient doses were quantified by determining the entrance skin dose with direct thermoluminescent dosimetry and by estimating the effective dose (E). Staff doses were quantified by determining the entrance skin dose at the level of the eyes, thyroid, and both the hands with direct thermoluminescent dosimetry. For a group of 82 consecutive patients, the following median values were determined (data per procedure): patient E (19.7 mSv), patient entrance skin dose (374 mSv), staff entrance skin dose at eye level (0.21 mSv), thyroid (0.24 mSv), at the left hand (0.18 mSv), and at the right hand (0.76 mSv). The maximum recorded patient entrance skin dose stayed well below the deterministic threshold level of 2 Gy. Poor correlation between both patient/staff doses and integrated procedure mAs emphasizes the need for in vivo measurements. CT fluoroscopy doses are markedly higher than classic CT-scan doses and are comparable to doses from other interventional radiological procedures. They consequently require adequate radiation protection management. An important potential for dose reduction exists by limiting the fluoroscopic screening time and by reducing the tube current (mA) to a level sufficient to provide adequate image quality.

Imaging tutorial: differential diagnosis of bright lesions on diffusion-weighted MR images.

High sensitivity (94%) and specificity (100%) have been reported in the diagnosis of acute cerebral infarction with diffusion-weighted magnetic resonance (MR) imaging. However, high signal intensity on diffusion-weighted MR images and low apparent diffusion coefficient values (similar to the findings in acute cerebral infarction) were reported in such diverse conditions as hemorrhage, abscess, lymphoma, and even Creutzfeldt-Jakob disease. The differential diagnosis of these conditions (eg, acute ischemic infarction and acute cerebral hemorrhage) is critical for the determination of appropriate treatment. The authors present a systematic review of bright lesions on diffusion-weighted MR images and their differential diagnosis, with emphasis on the practical and clinical approaches of differential diagnosis.

Biliary atresia and cerebellar hypoplasia in polysplenia syndrome.

We report a 3.5-month-old boy with polysplenia syndrome who demonstrated hemiazygos continuation of the inferior vena cava, extrahepatic biliary atresia, multiple splenunculi, bowel malrotation, and the rare finding of brainstem and cerebellar hypoplasia. A possible pathogenesis for cerebellar hypoplasia in this syndrome is suggested after review of the literature. The importance of seeking associated anomalies in biliary atresia, which may be possible indicators of polysplenia syndrome, is stressed since these patients need appropriate management when surgery is considered.

Meniscal tears: comparison of half-Fourier technique and conventional MR imaging.

PURPOSE: To determine whether half-Fourier MR image acquisition technique can provide similar information to that of conventional MR acquisition technique for evaluation of meniscal tears. MATERIALS AND METHODS: We studied 101 menisci in 52 patients who were referred for evaluation of meniscal tears. Sagittal MR images of the knee were obtained for all patients by using proton density and T2-weighted SE sequences on a 1-T clinical system. The half-Fourier technique and conventional technique were used for all patients. All other imaging parameters were identical for both sequences (TR/TE=2400/20,70; 3 mm slice thickness; 200 x 256 matrix; field of view, 200; one signal acquired). Both sets of images were filmed with standard window and level settings. Images were randomised and interpreted independently by two radiologists for the presence of meniscal tears. Images were also subjectively assessed for image quality using a five-point grading scale. RESULTS: On half-Fourier images, Reader 1 interpreted 23 menisci as torn, compared to 28 for Reader 2. On conventional images, Reader 1 interpreted 24 menisci as torn, compared to 26 for Reader 2. Agreement between interpretation of the conventional and that of the half-Fourier images was 99% for Reader 1, and 98% for Reader 2. Agreement between readers for the half-Fourier images was 95%, and for the conventional images 96%. No statistically significant difference was found in the subjective evaluation of image quality between the conventional and half-Fourier images. CONCLUSION: The half-Fourier acquisition technique compares favourably with the conventional technique for the evaluation of meniscal tears.

Use of a curved-array transducer to reduce interobserver variation in sonographic measurement of thyroid volume in healthy adults.

PURPOSE: Sonographic calculation of thyroid volume is used in the diagnosis and follow-up of thyroid diseases. Since the calculated volume of thyroid lobes is highly influenced by the longest (ie, craniocaudal) diameter, we examined whether using a curved-array transducer as opposed to a linear-array transducer to measure the craniocaudal diameter would reduce interobserver variation. METHODS: Three sonographers with different levels of expertise each used a 5-12-MHz linear-array transducer and a 2-5-MHz curved-array transducer to measure the craniocaudal diameter of both thyroid lobes of 25 healthy volunteers. On the basis of these measurements, thyroid lobe volumes were calculated. Single-factor analysis of variance was used to evaluate the interobserver variations between the measurements made by all 3 observers as well as between measurements taken by pairs of observers. A p value of less than 0.05 was considered significant. RESULTS: Using the linear-array transducer to measure the craniocaudal diameter resulted in significant interobserver variation in thyroid volume calculation (p = 0.02), whereas using the convex-array transducer did not. Using either transducer resulted in a highly significant interobserver variation in measurements of the craniocaudal diameter, although the variation was far more pronounced for measurements made with the linear-array transducer (p = 0.0005) than for those made with the curved-array transducer (p = 0.04). For both transducers, the interobserver variations were most pronounced between the most and the least experienced sonographers. CONCLUSIONS: To avoid significant interobserver variation in calculating thyroid lobe volume, we recommend using a curved-array transducer to measure the craniocaudal diameter of the thyroid lobes.

Peroneal nerve injury in three patients with knee trauma: MR imaging and correlation with anatomic findings in volunteers and anatomic specimens.

The aim of this article is to report on three patients with injuries of the peroneal nerve along the posterolateral aspect of the knee. Injuries in this area are less common than the injuries occurring at the level of the fibular head. In this article we report on three patients with posterolateral knee trauma who had peroneal nerve dysfunction. To better understand the precise location of the nerve on MR images, we performed MR imaging in five volunteers, and studied the position of the nerve on anatomic dissection ( n=1) and anatomic slices ( n=1). The common peroneal nerve is easily depicted on MR images and has a typical location along the posterior margin of the biceps tendon. Non-visualisation of the peroneal nerve at the posterolateral aspect of the knee, as seen on MR images, is consistent with nerve injury. Scar tissue at the posterolateral aspect of the knee indicates injury of this specific area, and involvement of the peroneal nerve is likely.

Reducing inter-observer variation in thyroid volume calculation using a new formula and technique.

OBJECTIVE: Ultrasound (US) measurement of thyroid volume is used in diagnosis and follow-up of patients with thyroid disease. We assessed a new formula and technique for thyroid volume calculation, based on an automatically continuous trace transverse surface area (aTSA) calculation, to ascertain where this technique could reduce inter-observer variation. METHODS: Three observers with a different level of US expertise, using a 12-5 MHz linear transducer, examined 25 volunteers. Inter-observer variations were calculated for diameter measurements and for the thyroid lobe volume calculations using the single factor ANOVA method. RESULTS: Using the new technique and formula, no statistically significant differences existed, in contradistinction to using the classical formula for an ellipsoid (P=0.02). CONCLUSION: When thyroid volume measurements are required, we recommend using a new method of thyroid volume calculation based on the use of an automatically calculated continuous trace aTSA measurement to avoid significant inter-observer variation in calculation of thyroid lobe volumes.

Pathogenesis of venous stroke: evaluation with diffusion- and perfusion-weighted MRI.

Previous reports have demonstrated the diagnostic usefulness of diffusion- and perfusion-weighted magnetic resonance imaging (MRI) in the evaluation of cerebral venous thrombosis. However, the explanations ascribed for the pathophysiologic mechanisms of venous stroke in these reports were conflicting. Earlier reports supported prominent vasogenic edema associated with mild cytotoxic edema as the potential pathophysiologic mechanism. More recently, a few reports have found cytotoxic edema as the cause for venous stroke. The purpose of this report is to review the pathogenesis of cerebral venous thrombosis after taking into consideration the results of MRI findings. We report two cases of cerebral venous infarction, which had worsening symptoms and signs that resolved after intravenous heparin therapy. In both cases, findings on diffusion-weighted and perfusion-weighted MRI images were compatible with vasogenic edema and viable neuronal tissue. Both the patients recovered without any significant residual sequel. We support the hypothesis that in the pathogenesis of venous stroke vasogenic edema is the initial event, which may or may not be followed by cytotoxic edema eventually evolving to an infarction.

Study of pediatric brain development using magnetic resonance imaging of anisotropic diffusion.

The properties of water diffusion in human brain tissue can be characterized by diffusion tensors computed from diffusion weighted magnetic resonance images. Since these properties are strongly determined by the structural and geometrical characteristics of the tissue, the maturation process of white matter and gray matter tissue can be expected to be reflected in these images and derived tensor quantities. The purpose of this work was therefore to study the development of pediatric brain in terms of changes occurring in the observed diffusion behavior. Echo planar diffusion tensor imaging was performed on 22 (10 females and 12 males) full term newborn and infant patients, diagnosed in retrospect as neurologically healthy. The subjects were subdivided in three age categories. A number of quantities based on the diffusion images were calculated for each tissue type and age category, and the ability of these quantities to provide sensitive and consistent information about the tissue differences and evolution was evaluated. The results clearly illustrate that the rotationally invariant quantities (e.g., the highest diffusivity, anisotropy ratio and volume ratio) are superior to the rotationally variant ones (e.g., ADCs measured along the three axes of the magnet) often used in the clinic. On the basis of the anisotropy ratio and the volume ratio indices, a correlation between the white matter maturation and the evolution of the diffusion anisotropy could be established. The same quantities did not exhibit any age dependence for the gray matter tissues.

Sonography of the medial and lateral tendons and ligaments of the knee: the use of bony landmarks as an easy method for identification.

OBJECTIVE: Our purpose was to describe the use of bony landmarks in the evaluation of the medial and lateral ligaments and tendons of the knee on sonography and to evaluate the value of this approach in healthy volunteers. MATERIALS AND METHODS: Anatomic slices obtained in cadaveric specimens were inspected for the presence of bony landmarks on the medial and lateral aspects of the knee. Then sonography was performed on 40 knees of 20 healthy volunteers by two musculoskeletal radiologists who independently rated the visualization of bony landmarks and adjacent ligaments and tendons on a 5-point grading scale. RESULTS: Bony landmarks on the lateral aspect of the knee include Gerdy's tubercle on the tibia and the sulcus for the popliteal tendon on the femur. Landmarks on the medial aspect of the knee include the medial epicondyle on the femur and the sulcus for the semimembranosus tendon on the tibia. Visualization of all landmarks was rated in the good to excellent range, and agreement between observers ranged from 92.5% to 100%. CONCLUSION: Bony landmarks can be identified in healthy adults on the medial and lateral aspects of the knee and may serve as reference points for identification of most medial and lateral tendons and ligaments.

Medial meniscocapsular separation: MR imaging criteria and diagnostic pitfalls.

Various magnetic resonance imaging (MRI) signs can be used in the diagnosis of medial meniscocapsular separation. A thorough knowledge of the normal anatomy of the medial meniscocapsular junction is essential to understand these signs. MRI signs used in the diagnosis of meniscocapsular separation include meniscal displacement relative to the tibia, meniscal corner tear, perimeniscal fluid, irregular meniscal outline, meniscofemoral and meniscotibial extension tears, and interposition of contrast medium between the meniscus and the MCL. Potential causes of false positive diagnosis of meniscocapsular separation include MCL bursitis, meniscal cyst, MCL tear, joint effusion, and perimeniscal fat.