Susceptibility-weighted imaging of the brain: Does gadolinium administration matter?

Objective

Susceptibility-weighted MR imaging (SWI) is usually obtained without administration of intravenous gadolinium (Gd). However, it is occasionally necessary to perform SWI after Gd is injected. The effects of Gd on SWI have not been systematically examined. The aim of this prospective study was to investigate whether performing SWI after Gd would influence the diagnostic image quality, parenchymal signal and vascular enhancement. An additional aim is to suggest potential future applications for Gd-enhanced SWI.

Methods

SWI was performed in 31 subjects before and after Gd administration. 17 cases were examined in a 1.5 T scanner and the remaining 14 were scanned at 3 T. The pre- and post-Gd images were analysed for signal changes in the cerebral grey matter (GM), white matter (WM) as well as for enhancement in the superficial and deep venous system. The visibility of the veins was graded on subtraction maps.

Results

The Gd-enhanced images showed no image quality degradation and no significant signal intensity change in the GM and WM as compared to the pre-Gd images (p > 0.05). After Gd-administration significant enhancement of the venous sinuses was noticed (p < 0.005), while the deep and cortical veins were poorly enhanced as confirmed by the calculated subtraction maps. The results showed no significant difference at variable MRI field strengths.

Conclusion

It is possible to perform SWI after Gd injection without information loss or signal change in the parenchyma. The most significant difference is the enhancement of the cerebral venous sinuses. Potential future applications are discussed.     

Clinical applications of susceptibility weighted MR imaging of the brain – a pictorial review

Introduction Susceptibility-weighted imaging (SWI) is a novel magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification. This pictorial review covers many clinical conditions illustrating its usefulness. Methods SWI consists of using both magnitude and phase images from a high-resolution, three-dimensional fully velocity-compensated gradient echo sequence. Phase mask is created from the MR phase images, and multiplying these with the magnitude images increase the conspicuity of the smaller veins and other sources of susceptibility effects, which is depicted using minimal intensity projection (minIP). Results The phase images are useful in differentiating between diamagnetic and paramagnetic susceptibility effects of calcium and blood, respectively. This unique MR sequence will help in detecting occult low flow vascular lesions, calcification and cerebral microbleed in various pathologic conditions and aids in characterizing tumors and degenerative diseases of the brain. This sequence also can be used to visualize normal brain structures with conspicuity. Conclusion Susceptibility-weighted imaging is useful in differentiating and characterizing diverse brain pathologies.     

MRI of the brain in HIV-positive patients: what is the value of routine intravenous contrast medium?

Our purpose was to assess the value of routine administration of intravenous gadolinium-DTPA (Gd-DTPA) for cranial MR in a series of human immunodeficiency virus (HIV)-positive patients. Two radiologists retrospectively reviewed 150 consecutive examinations of 104 patients. All patients underwent unenhanced and contrast-enhanced images. Each radiologist independently assessed first the unenhanced images alone and then the pre- and postinjection images together. Then both reviewed the complete study and produced a consensus report. The history, investigations and management were collated separately and were unknown to the radiologists. Contrast-enhanced T1-weighted images showed new focal abnormalities, not seen on the T2-weighted or unenhanced images in 15 (14 %) patients, but almost always in the context of abnormal unenhanced images. In only 2 patients (2 %) did contrast medium reveal abnormalities when the unenhanced study had been considered normal. In only 1 of these (1 %) was the new finding, cytomegalovirus diffuse ependymal enhancement, of clinical importance, although the diagnosis of encephalitis was made on routine examination of cerebrospinal-fluid. The other revealed a toxoplasma lesion in a patient known to have resolving disease. Meningeal disease not suspected on the unenhanced images was shown in 2 patients (2 %). In these case the unenhanced images were abnormal in other respects. Intravenous Gd-DTPA was helpful to the radiologist in making a radiological diagnosis in 11 patients (11 %), usually by improving characterisation of a lesion seen on the unenhanced images. The contribution of intravenous Gd-DTPA in this series does not warrant recommending its use in every case. Received: 21December 1998 Accepted: 29 December 1998     

Determination of the optimal ROI setting position of the input function for the ⁹⁹mTc-ethyl cysteinate dimmer brain uptake ratio method

Determination of the input function for the (99m)Tc-ethyl cysteinate dimmer brain uptake ratio ((99m)Tc-ECD BUR) method as a non-invasive quantitative measurement of cerebral blood flow measurement is of critical importance in order to improve the accuracy of this method. The input functions were experimentally obtained by setting the regions of interest (ROIs) in the ascending aorta, aortic arch, and descending aorta on the 49 chest RI-angio images. rCBFs by the BUR method with 3 input functions of the 6 cases were compared with those by the (123)I-iodoamphetamine (IMP) continuous arterial blood sampling method in order to determine the best location for the ROI of the input function. The input function of the ascending aorta was higher than those of the aortic arch and the descending aorta. The input functions of the aortic arch and the descending aorta decreased due to the origin of the three branches of the right brachiocephalic artery, left subclavian artery, and left common carotid artery. A good correlation was found in the regional cerebral blood flow (rCBF) values between the (123)I-IMP continuous arterial blood sampling method and the (99m)Tc-ECD BUR method with the input function of the ascending aorta. Therefore, the ascending aorta is the best location for the ROI of the input function for the (99m)Tc-ECD BUR method.     

The “mini brain” appearance of plasmacytoma in the appendicular skeleton

We report on the case of a 70-year-old woman presenting with right hip pain. Radiographs of the right hip demonstrated a well-defined large lytic lesion in the proximal right femur, with prominent trabeculae situated peripherally and extending into the lesion in a "spoke-wheel" pattern. Magnetic resonance imaging (MRI) demonstrated solid enhancing marrow-replacing lesion, with intervening linear nonenhancing areas of low T2 signal intensity. The MRI appearance resembled that of a small brain or "mini brain". Biopsy specimen demonstrated predominantly mature plasma cells, with occasional admixed immature forms. A diagnosis of plasmacytosis, consistent with myeloma, was made. This case illustrates a rare but seemingly characteristic "mini brain" appearance of plasmacytoma, which, to date, has only been reported in the spine and has not been observed in other bony lesions.     

Regional distribution of serotonin transporter protein in postmortem human brain: is the cerebellum a SERT-free brain region?

INTRODUCTION: The primary approach in assessing the status of brain serotonin neurons in human conditions such as major depression and exposure to the illicit drug ecstasy has been the use of neuroimaging procedures involving radiotracers that bind to the serotonin transporter (SERT). However, there has been no consistency in the selection of a "SERT-free" reference region for the estimation of free and nonspecific binding, as occipital cortex, cerebellum and white matter have all been employed. OBJECTIVE AND METHODS: To identify areas of human brain that might have very low SERT levels, we measured, by a semiquantitative Western blotting procedure, SERT protein immunoreactivity throughout the postmortem brain of seven normal adult subjects. RESULTS: Serotonin transporter could be quantitated in all examined brain areas. However, the SERT concentration in cerebellar cortex and white matter were only at trace values, being approximately 20% of average cerebral cortex and 5% of average striatum values. CONCLUSION: Although none of the examined brain areas are completely free of SERT, human cerebellar cortex has low SERT binding as compared to other examined brain regions, with the exception of white matter. Since the cerebellar cortical SERT binding is not zero, this region will not be a suitable reference region for SERT radioligands with very low free and nonspecific binding. For SERT radioligands with reasonably high free and nonspecific binding, the cerebellar cortex should be a useful reference region, provided other necessary radioligand assumptions are met.     

Can a comparison of clinical and deep space irradiation scenarios shed light on the radiation response of the brain?

Not surprisingly, our knowledge of the impact of radiation on the brain has evolved considerably. Decades of work have struggled with identifying the critical cellular targets in the brain, the latency of functional change and understanding how irradiation alters the balance between excitatory and inhibitory circuits. Radiation-induced cell kill following clinical fractionation paradigms pointed to both stromal and parenchymal targets but also defined an exquisite sensitivity of neurogenic populations of newly born cells in the brain. It became more and more apparent too, that acute (days) events transpiring after exposure were poorly prognostic of the late (months-years) waves of radiation injury believed to underlie neurocognitive deficits. Much of these gaps in knowledge persisted as NASA became interested in how exposure to much different radiation types, doses and dose rates that characterize the space radiation environment might impair central nervous system functionality, with possibly negative implications for deep space travel. Now emerging evidence from researchers engaged in clinical, translational and environmental radiation sciences have begun to fill these gaps and have uncovered some surprising similarities in the response of the brain to seemingly disparate exposure scenarios. This article highlights many of the commonalities between the vastly different irradiation paradigms that distinguish clinical treatments from occupational exposures in deep space.     

Disruption of the blood–brain barrier by intra-arterial administration of papaverine: a technical note

Introduction  Various endovascular techniques can be used to treat cerebral vasospasm after aneurysmal subarachnoid haemorrhage (SAH) including intra-arterial administration of vasodilator drugs such as papaverine or nicardipine and balloon dilatation of the affected vessel segment. Papaverine is known to have side effects, and we report a possible new one. Materials and methods  After the treatment of cerebral vasospasm in a SAH patient by intra-arterial administration of papaverine into the left posterior cerebral artery, severe mesencephalic extravasation of blood and contrast media was detected. Results  After reviewing the literature, the authors conclude that interruption of the blood–brain barrier by papaverine most likely combined with a secondary hyperperfusion phenomena, and perhaps a direct toxic effect on brain tissue was the mechanism of this major complication. Conclusion  In treating vasospasm in areas with a high density of perforating arteries, especially in the posterior circulation, papaverine should be used cautiously because a safe regimen has yet to be established. In this situation, alternative agents such as calcium channel blockers could be considered, but evidence-based data are still missing.     

Where have we got to with neuroreceptor mapping of the human brain?

In the past two decades, tritiated radioligand receptor binding, a tool commonly used to investigate the site of action of drugs in laboratory animals, has provided a vast body of information on neuropharmacology and neurobiology. Several neurological and psychiatric diseases have been related to neurotransmitter and receptor disorders. In order to study ligand interactions with receptors in vivo in humans, new tracers capable of carrying a-emitting radionuclide to the receptor have been designed. Emission computerized tomography (ECT) techniques such as positron (PET) or single photon emission tomography (SPET) allow monitoring of the time-course of regional tissue concentration of these radiolabelled ligands. PET and SPET each have their inherent advantages and drawbacks. The cyclotron-based technology of PET is a demanding and expensive technique that, to date, is still mainly reserved for research purposes. It is hoped that once the scientific basis of a physiopathological study is established using PET, diagnostic information might be provided by the more readily available SPET technology. The purpose of this article is to review the current state of receptor-binding-emitting radioligands and to present the clinical potential of these new kinds of radiopharmaceuticals in clinical investigation.     

Imaging genetics of brain longevity and mental wellness: the next frontier?

The advent of new "omics" technologies (genomics, proteomics, and metabolomics) has ushered in a new era of biomedical discovery that is already affecting every field of medicine. With the rapid growth of the older population worldwide, there is great interest in applying these technologies not only to diagnose and prevent disease, but also to enhance brain longevity and mental wellness. Nearly two-thirds of the approximately 30,000 genes in the human genome are related to brain function, and up to half of the variance in age-related changes in cognition, brain volume, and neuronal function appears to be genetically determined. Selected examples will be used to illustrate how neuroimaging is being employed to study the effects of genes and how neurogenetics may affect future radiology research and practice.     

Proton MR spectroscopy of the brain at 3 T: an update

Proton magnetic resonance spectroscopy (¹H-MRS) provides specific metabolic information not otherwise observable by any other imaging method. ¹H-MRS of the brain at 3 T is a new tool in the modern neuroradiological armamentarium whose main advantages, with respect to the well-established and technologically advanced 1.5-T ¹H-MRS, include a higher signal-to-noise ratio, with a consequent increase in spatial and temporal resolutions, and better spectral resolution. These advantages allow the acquisition of higher quality and more easily quantifiable spectra in smaller voxels and/or in shorter times, and increase the sensitivity in metabolite detection. However, these advantages may be hampered by intrinsic field-dependent technical issues, such as decreased T₂ signal, chemical shift dispersion errors, J-modulation anomalies, increased magnetic susceptibility, eddy current artifacts, challenges in designing and obtaining appropriate radiofrequency coils, magnetic field instability and safety hazards. All these limitations have been tackled by manufacturers and researchers and have received one or more solutions. Furthermore, advanced ¹H-MRS techniques, such as specific spectral editing, fast ¹H-MRS imaging and diffusion tensor ¹H-MRS imaging, have been successfully implemented at 3 T. However, easier and more robust implementations of these techniques are still needed before they can become more widely used and undertake most of the clinical and research ¹H-MRS applications.     

Fatal brain injury caused by the free-flying blade of a knife – case report and evaluation of the unusual weapon

A man suffered a fatal injury from a self-inflicted accident while handling a special type of knife. A spring in the shaft of the knife accelerated the blade, which perforated the orbital cavity and the frontal lobe at the right side. Death was due to central disregulation. The initial velocity of the blade was measured to be 15 m/s. In a total of 20 experimental shots to a fresh pig cadaver, the blade always penetrated the skin and 5–10 cm of soft tissue as long as the distance did not exceed 1 m. Thin layers of bone were also perforated. The free flight of the blade did not remain stable if the distance was more than 1 m, which resulted in superficial wounds only. So this unusual construction resembling a knife can be considered an effective combat weapon for close range fighting instead of a tool. Received: 18 January 1999 / Accepted: 27 January 1999     

Is the center of mass (COM) a reliable parameter for the localization of brain function in fMRI?

The center of mass (COM) in functional MRI studies is defined as the center of a cerebral activation cluster. Although the COM is a well-accepted parameter for exactly localizing brain function, the reliability of COMs has not received much attention until now. Our goal was to investigate COM reliability as a function of the thresholding technique, the threshold level, and the type of COM calculation. Therefore 15 subjects were examined repeatedly using simple hand and tongue movement paradigms. Postprocessing was performed with uncorrected, corrected, and proportional thresholding as well as different threshold levels. Geometric and T-weighted COMs of left-hemispheric primary hand and tongue motor clusters were calculated. The COM variation was evaluated within and between repeated sessions depending on the different postprocessing setups. Mean COM variations over three repeated sessions varied between 1.6 mm and 9.8 mm for the hand paradigm and between 7.0 mm and 14.4 mm for the tongue task. Stringent thresholding techniques and high threshold levels were required to assess reliable results, whereas the kind of COM calculation was of lesser relevance. Thus, COM reliability cannot be presupposed; it depends strongly on the individual postprocessing techniques. This should be considered when using COMs for localizing brain function.     

How does the blood leave the brain? A systematic ultrasound analysis of cerebral venous drainage patterns

The internal jugular veins are considered to be the main pathways of cerebral blood drainage. However, angiographic and anatomical studies show a wide anatomical variability and varying degrees of jugular and non-jugular venous drainage. The study systematically analyses the types and prevalence of human cerebral venous outflow patterns by ultrasound and MRI. Fifty healthy volunteers (21 females; 29 males; mean age 27±7 years) were studied by color-coded duplex sonography. Venous blood volume flow was measured in both internal jugular and vertebral veins in the supine position. Furthermore, the global arterial cerebral blood volume flow was calculated as the sum of volume flows in both internal carotid and vertebral arteries. Three types of venous drainage patterns were defined: a total jugular volume flow of more than 2/3 (type 1), between 1/3 and 2/3 (type 2) and less than 1/3 (type 3) of the global arterial blood flow. 2D TOF MR-venography was performed exemplarily in one subject with type-1 and in two subjects with type-3 drainage. Type-1 drainage was present in 36 subjects (72%), type 2 in 11 subjects (22%) and type 3 in 3 subjects (6%). In the majority of subjects in our study population, the internal jugular veins were indeed the main drainage vessels in the supine body position. However, a predominantly non-jugular drainage pattern was found in approximately 6% of subjects.This study was presented in part as an oral presentation at the 8th Meeting of Neurosonology and Hemodynamics, Alicante, Spain, 18–21 May 2003.     

Evaluation of the effects of chemotherapy on brain glucose metabolism in children with Hodgkin’s lymphoma

Annals of Nuclear Medicine - Chemobrain is a recently proposed pathological entity. 18F-FDG PET/CT can show objective abnormalities to explain brain disorders caused by chemotherapy, although no...