Neuroradiology
Figure 3: A 73-year-old Man with Primary Glioma and Clinical Symptoms of Seizures and Headache
FLAIR Gadobutrol 5 min
Gadofosveset Trisodium 5 min
gadofosveset-trisodium-based contrast-enhanced MRI were localized to the same areas, indicating that blood pool agents can be used to determine the functional consequences of tumors and tumor therapy.52
Perfusion-weighted Magnetic Resonance Imaging Alterations in regional cerebral blood flow (rCBF) and volume (rCBV) due to the increased vascularization of tumors may be biomarkers for intracranial lesions, therefore PWI is typically used in conjunction with conventional imaging to provide additional information about cerebral hemodynamics, improving overall tumor detection, diagnosis, grading and treatment.9,53–58
3h
6h
24h
The high-intravenous concentration of a Gd-based contrast agent following a rapid intravenous bolus injection causes T2* relaxation effects that outweigh T1 effects so that the first pass of the bolus is seen as a drop in signal intensity within the lesion in T2*-weighted echoplanar images. The change in relaxation times can be converted to a tissue contrast agent concentration from which it is possible to calculate rCBF and rCBV as well as the transit time and the time to peak.54,59–61
Since the
degree of signal intensity loss is a reflection of the amount of contrast agent in the cerebrovasculature,62
by increasing contrast agent concentration.63
contrast enhancement can be improved Moreover, agents with
Axial fluid-attenuated inversion recovery (FLAIR) image revealed a large infiltrating tumor in the right temporal lobe with strong enhancement after gadobutrol injection. On images obtained three and six hours after gadofosveset trisodium administration, the enhancement was stronger and the margins of the lesion were better delineated. Late acquisitions show the internal structure of the tumor much better. Gadofosveset provides more diagnostic information.
dimeglumine. All studies noted a preference for gadobenate dimeglumine over the standard contrast agent for lesion enhancement and most diagnostic endpoints, irrespective of the standard contrast agent used, gadopentetate dimeglumine, gadoterate meglumine or gadodiamide, the strength of the magnetic field, or whether the blinded readers were on site or off site.44–50
To date, only a single study has evaluated the potential of gadofosveset trisodium for enhancement of intracranial tumors. In a cohort of 10 patients, gadofosveset trisodium was compared with gadopentetate dimeglumine.51 Despite the lower dose of gadofosveset trisodium (0.03 mM/kg body weight) compared with gadopentetate dimeglumine (0.1 mM/kg), lesion enhancement was increased (see Figures 1 and 2). Furthermore, in one instance, gadofosveset trisodium identified a low-grade astrocytoma that could not be visualized using gadopentetate dimeglumine due to its longer intravascular retention time.51
This preliminary study shows that
blood pool agents can be used for tumor enhancement with standard contrast-enhanced MRI, but more detailed studies in larger populations are required to identify where and when their use would be of most benefit. Blood pool agents may provide greater diagnostic information endpoints of brain tumor and may further contribute to improved patient management (see Figure 3). In a separate study, the effectiveness of gadofosveset-trisodium-based contrast-enhanced MRI for establishing functional cortical maps pre- and post-surgical intervention in patients with brain tumor was examined.52
Comparison with blood-oxygen-level-dependent (BOLD) functional MRI (fMRI) showed that maximum activations using 12
higher relaxivity rates should also improve contrast enhancement for PWI, as demonstrated for both gadobutrol and gadobenate dimeglumine.64–66 Blood pool agents should also be good candidates for contrast enhancement in PWI due to their intravascular retention and resultant high relaxivity rates, thereby enabling precise delineation of the cerebrovascular system. Despite this possibility, no studies have yet examined the suitability of gadofosveset trisodium for PWI.
Contrast-enhanced Magnetic Resonance Imaging in Acute Stroke
The function of MRI in acute stroke is to confirm the diagnosis and identify potential therapeutic strategies. In doing so, MRI can assess pre-existing lesions, locate the thrombus, classify the type of stroke, evaluate blood supply and define the extent of the injury and the approximate time of the ischemia onset.15,67,68
BBB breakdown has been used to assess stroke,34
Although standard contrast-enhanced MRI of the PWI is more commonly
used as the drop in CBF is a clear indicator of tissue necrosis and estimates of severity can be obtained by comparison of the affected and unaffected hemispheres.69
Importantly, the mismatch
between PWI and DWI may be used to delineate tissue at risk for infarction but potentially treatable by prompt thrombolytic therapy.72–74
However, the mainstay of stroke MRI is DWI, which provides information on the presence of reversibly and irreversibly damaged tissue and does not require contrast enhancement.70,71
Contrast
agents that improve current standards of PWI, including blood pool agents with high relaxivity rates, are therefore likely to improve stroke diagnosis and patient outcomes. To date, however, few studies have used contrast agents with high relaxivity rates to assess stroke,65 used gadofosveset trisodium.
and no studies have
Additional Uses of High-relaxivity Contrast Agents in Neuroimaging
Conventional MRI is a routine diagnostic tool for multiple sclerosis (MS) and Gd-enhanced T1-weighted sequences are highly sensitive for detecting MS plaques and inflammation,75,76
although the relationship
between MRI-detected pathologies and clinical manifestations of the disease are unclear.77
Contrast-enhanced MRI can discount alternative US RADIOLOGY
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