Current Medical Imaging - Volume 4, Issue 3, 2008

This issue again presents advanced MR imaging techniques to study of somatosensory-motor processing and multiple sclerosis, MR cisternography and myelography, quantitative ultrasound for fetal growth and skeletal status, and various techniques to visualize DNA repair proteins. Magnetic encephalography (MEG) has been used to measure the magnetic field produced by electrical activity in the brain via extremely sensitive devices such as superconducting quantum interference devices. This assists a localization of pathologic lesions and determination of functional parts of the brain. Drs. Kida and Kakigi review basic concepts of MEG in comparison with EEG and clinical studies of attention and somatosensory-motor interaction as well as movement disorders. Multiple sclerosis (MS) is characterized by inflammation and scarring of the CNS, and MS plaques are often hypointense to white matter on precontrast T-1-weighted images. However, this finding lacks a specificity since many other diseases can produce white matter lesions with similar appearance. There is a poor association between clinical and radiological findings. Hypointense spinal cord lesions on T1-weighted images correlate better with functional disability than brain lesions, possibly because cord lesions are more likely to involve motor tracts. Dr. Lenzi et al. discuss functional MRI studies to demonstrate a brain reorganization or adaptive mechanism in patients with MS. Cisternography using intrathecal contrast agent has been used for many years in the diagnostic evaluation of disease processes involving the basilar cisterns and skull base, and myelography has also been an important diagnostic modality for a wide range of spinal diseases. Injection of Gd-DTPA into the subarachnoid space can enhance the contrast between CSF, brain, spinal cord and surrounding meninges and bones. This is very helpful to evaluate tumors adjacent to the CSF spaces, abnormal CSF collections, CSF rhinorrhea and otorrehea, syringohydromyelia, and studies of hydrocephalus as well as CSF flow dynamics. Drs. Sprague and Berkman report a case of compression fracture secondary to cement leakage into the disc space during the vertebroplasty procedure. Ultrasound (US) is an inexpensive and widely used imaging modality for the diagnosis and evaluation of a number of diseases. In the last decade, investigators and commercial companies have advanced US imaging with the development of 3D technique. This new imaging approach is rapidly achieving widespread use with numerous applications. Drs. Hata and Dai review quantitative 3D power Doppler in the assessment of the vascularization and blood flow of the fetal organs and placenta for the evaluation of fetal growth and development. Quantitative US (QUS) measures the US beam changes when it passes through the bone, called as broad band ultrasonic attenuation, and also measures the speed at which the beam passes. It has proven its utility in the detection of skeletal changes in various disorders. There is also an increasing interest for the screening of osteoporosis since it predicts fracture risk. Dr. Halaba discusses the usefulness of phalageal QUS in the assessment of skeletal status in children and adolescents. Cells continuously suffer from DNA damage and all cells must quickly mend any breaks that occur in their DNA strands. The double strand break (DSB) is most dangerous one due to the potential development of cancer. Cancer cells are dependent on a process called homologous recombination to repair DNA and stay alive. That is what makes them resistant to drug or radiation therapy. Dr. Krawczyk et al. summarizes different techniques that can be used to visualize proteins involved in DSB repair process. They are X-ray crystallography, confocal, electron, fluorescence or scanning force microscopy, immunocytochemistry, fluorescence resonance energy transfer, and fluorescence recovery after photobleaching.

Recent advances in neuroimaging techniques have unveiled the functional localization and timing of neural activations associated with a variety of brain functions. This review focuses on the timing of neural activations related to attentional and sensory-motor functions in the somatosensory system as revealed by high-temporal resolution neuroimaging studies using magnetoencephalography (MEG) and electroencephalography (EEG). We will briefly review basic concepts of EEG and MEG, and then EEG and MEG studies of attention and somatosensorymotor interaction while referring to previous studies using other techniques. Findings from patients with movement disorders will be also summarized. An overview of these studies shows that EEG and MEG are helpful to reveal cortical dynamics of attentional and sensory-motor processing in the human brain and potentially a powerful tool to evaluate the pathophysiology of relevant disorders.

The diagnosis of multiple sclerosis (MS) and the consequent therapeutic choices have been rendered considerably easier by the advent of magnetic resonance imaging; however, conventional MR images alone do not fully explain the clinical severity of MS patients; this poor correlation between clinical and radiological findings has been referred to as the clinico-radiological paradox. Histological studies and non-conventional MRI have shown that MS alterations are not confined to white matter lesions, but may be found in both normal-appearing white matter (NAWM) and in grey matter. It has been established that irreversible tissue damage in MS leads to disability; it should, however, be borne in mind that the clinical outcome in MS patients is the result of a balance between the severity of damage to the central nervous system and the effectiveness of the repair and recovery mechanisms in such patients. These plastic changes are believed to underlie the changes in functional activity that can be observed during functional magnetic resonance (fMRI) studies. In patients with MS, functional brain reorganization mainly consists of an increase, if compared with healthy subjects, in the extent of activation in the affected brain areas, as well as the recruitment of additional brain areas. These findings have been interpreted as adaptive mechanisms that allow normal performance despite neural damage or loss. However, recent studies suggest that brain functional activity changes may merely be an epiphenomenon due to neuronal damage.

Context: Intravenous administration of contrast materials in imaging studies is critical in detection of lesions which may be otherwise missed. Both computed tomography (CT) and magnetic resonance imaging (MRI) benefit from addition of contrast agents. MRI is superior to CT in evaluation of most diseases involving the brain and spine. Contrast resolution and anatomic display are two of the main factors that contribute to the superiority of MRI. Disorders affecting the cerebrospinal fluid (CSF) containing spaces may be under-diagnosed or poorly understood on conventional CT or MRI. Although intrathecal CT-cysternography/myelography with water-soluble iodinated contrast media and radionuclide cisternography (RC) are routinely used, few studies have dealt with intrathecal use of Gadolinium (gadopentetate dimeglumine) (Gd) although it appears superior to both techniques and seems to be potentially less risky. Currently, Gdenhanced MRI cisternography/myelography is not approved by the US Food and Drug Administration and is used offlabel. Objective: i-To summarize the existing literature regarding the use, safety, and indications of intrathecal and intraventricular use of paramagnetic contrast MRI agents, specifically intrathecal Gd-enhanced cisternography or myelography; ii-To outline the technical procedures, safety, and indications, and iii-To provide a critical comparison with other approved studies such as CT-cysternography/myelography and RC. Methods: We reviewed the literature by MEDLINE searches using the terms gadopentate dimeglumine, gadodiamide, diethylenetriaminepentaacetic acid (Gd-DTPA), MRI-cysternography/ventriculography, intrathecal Gd-enhancement, CSF leaks, intracranial hypotension syndrome, spontaneous rhinorrhea and otorrhea, radioisotope cisternography. Reference lists of these articles and ongoing investigations in this area were used as well. Evidence Synthesis: There are no grade III studies of scientific evidence in comparative studies. The major drawback of available comparative studies, which evaluate the accuracy of each imaging technique, including enhanced-MR or CTcisternography/ myelography or RC, is the lack of a recognized “gold standard” imaging study, so that sensitivity or specificity of each imaging study cannot be fully assessed. Currently available studies demonstrate a superiority of intrathecal Gd MRI over CT cisternography/myelography and RC in some applications such as spontaneous or postoperative cranial fistulae, hypotension intracranial syndrome, and specific neurological/neurosurgical diseases of children. Superiority and safety of Gd-enhanced MR cisternography/ventriculography rests on absence of ionizing radiation, absence of bone artifacts, and superior spatial anatomic detail coupled with relatively high contrast resolution. Side effects and toxicity are low. Conclusions: It is unlikely that further studies will compare the efficacy of Gd-enhanced MR cisternography/ventriculography with their CT or RC counterparts since it is unethical to perform two intrathecal enhanced imaging examinations on the same patient. Although still not approved for clinical use worldwide, Gd-enhanced MR cisternography/ myelography seems to be clinically more useful and less risky than CT-cisternography/myelography and RC in certain complex central nervous system (CNS) diseases. Adverse effects, potential lumbar puncture-related side effects, and uncertain effects on the maturing brain and absence of long-term follow-up in patients who have undergone this procedure contribute to the underutilization of Gd-enhanced MR cisternography/myelography.

An elderly female underwent three level vertebroplasty for painful compression fractures of the thoracolumbar junction. During injection of the third level, she developed severe pain resulting from an acute adjacent level fracture secondary to substantial cement leakage into the disc space. This was recognized and treated immediately with vertebroplasty resulting in complete pain relief. To our knowledge, this is the first reported case of intraprocedural compression fracture secondary to cement leakage into the disc space.

We present herein modern three-dimensional (3D) sonographic studies on fetal growth and development, and various fetal volume measurements. The introduction of 3D ultrasound would allow for the assessment of fetal soft tissue deposition, fetal weight estimation, and the volume calculation of fetal organs. With the recent advance in the 3D power Doppler ultrasound as well as the quantitative 3D histogram analysis, quantitative 3D power Doppler in the assessment of the vascularization and the blood flow of the fetal organs and placenta has become feasible. These novel techniques may assist in the evaluation of fetal growth and development, and offer the potential advantages relative to conventional twodimensional fetal growth assessments. 3D ultrasound may be an important modality in future fetal growth and developmental research and in evaluation of fetal growth abnormalities.

Although dual energy x-ray absorptiometry (DXA) is the method considered to be the gold standard in pediatrics we must keep the disadvantages of this method in mind while trying to develop other more effective diagnostic tools for use in the pediatric population. In recent years, the method of quantitative ultrasound (QUS) has been developed for assessing bone properties. Low-frequency ultrasound travels across bone with a velocity that is related to bone quality and density. Furthermore, QUS techniques may be less influenced by bone size and can reveal physical properties of bone determined by bone composition and by structure. QUS is also void of ionizing radiation, cost-effective, portable and easy to use features which are beneficial in pediatrics. QUS systems exist for measurements at various skeletal sites such as calcaneous, phalanges, tibia and patella. Phalangeal QUS measurements have shown the ability to reveal changes due to skeletal growth, aging, and diseases. Large child and adolescent populations were measured and trends of changes in the measured ultrasound parameter during childhood and puberty were comparable with those shown in studies using DXA measurements. In case-control studies QUS proved its utility in the detection of skeletal changes in subjects with genetic disorders, renal osteodystrophy, acute lymphoblastic leukemia and in subjects treated with gonadotrophin-releasing hormone. There are also some longitudinal studies; in healthy children and adolescents and in survivors of malignant bone tumors and acute lymphoblastic leukemia, in subjects with renal insufficiency and in subjects with genetic disorders. Recently, phalangeal QUS and DXA measurements were compared in healthy subjects and have shown that QUS has the potential to express bone changes in measurements comparable to DXA.

DNA double-strand break (DSB) signaling and repair processes are positioned at the crossroad of nuclear pathways that regulate DNA replication, cell division, senescence and apoptosis. Importantly, errors in DSB repair may lead to lethal or potentially tumorigenic chromosome rearrangements. Therefore, understanding cellular DSB response mechanisms is important for both cancer prevention and treatment. Visualization of DSB repair proteins, both at the level of single molecules and at the level of cells and tissues is a powerful tool in unraveling DNA damage response. This review summarizes several available techniques for visualization of DSB repair proteins and describes types of information that can be obtained using these techniques.