MAGNETIC RESONANCE IMAGING By PROF. JORDI RUSCALLEDA
Contrast agent relaxivity or concentration? What really
makes the difference Gadobenate dimeglumine (MultiHance) has been shown to be advantageous compared with other gadolinium-based contrast agents for contrast-enhanced brain tumor MR imaging. This paper describes the results of the MERIT study which was an intra-individual comparison of 0.1 mmol/kg doses of gadobenate dimeglumine and gadobutrol (Gadovist) for qualitative and quantitative evalua- tion of brain tumors. Significantly greater morphologic information and lesion enhancement were achieved with 0.1-mmol/kg gadobenate dimeglumine compared with gadobutrol at an equivalent dose.
C
ontrast-enhanced MR imaging is universally considered the most sensitive diagnostic imaging technique for the visualization of brain tumors.
For the radiologist, the use of gadolinium-based MR con- trast agents (GBCAs) can improve the depiction of small or poorly visible lesions and facilitate their diagnosis and more accurate staging prior to selection of the most suit- able patient management option. For the neurosurgeon, contrast-enhanced MR images can provide invaluable information on the size and location of the lesion(s), on their relationship to surrounding struc- tures, and on the ease and appropriateness of resection. This is particularly important for intra-axial tumors such as gliomas since it is well known that these tumors often extend beyond the margins identified on T2-weighted MR images. Clearly, maximizing the amount of diagnos- tic information attained on enhanced MR images using GBCAs at their approved doses (invariably 0.1 mmol/kg body weight) will be beneficial in directing the appropri- ate therapy and improving overall patient outcome. The maximal amount of diagnostic information attained on enhanced MR images will be obtained if the most effica- cious MR contrast agent is used.
MR CONTRAST AGENTS
Of all the MR contrast agents currently approved for MR imaging of the CNS, unequivocal superiority has been consistently demonstrated for MultiHance (gado- benate dimeglumine, Bracco Imaging SpA, Milan, Italy), as reflected in the recently revised Summary of product
Prof. J Ruscalleda is at the Department of Neuroradiology, Hospital de la Santa Cruz y San Pablo-Barcelona, Barcelona, Spain. email:
JRuscalleda@santpau.cat
59 APRIL/MAY 2012 DI EUROPE 59 41
Characteristics (SPC) for this contrast agent [1]. Thus, in large-scale, multi-center clinical trials in which Mul- tiHance was compared directly, head-to-head, with com- parator MR contrast agents (namely Magnevist [2-6], Omniscan [7] or Dotarem [3, 8]) using an intra-individ- ual, crossover study design (i.e. a study design in which all patients receive both agents in two separate but otherwise identical MR examinations following a pre-defined ran- domization scheme) MultiHance demonstrated highly significant superiority in terms of all qualitative and quantitative evaluation end-points. This was demon- strated at magnetic field strengths of both 1.0-1.5T [2-5, 7, 8] and 3T [6]; in each case the increase in percent lesion enhancement on MultiHance-enhanced images relative to comparator-enhanced images corresponded roughly to the increase in percent lesion enhancement seen previ- ously for a double dose of comparator agent relative to a single dose of comparator agent [9].
RELAXIVITY
Like other GBCAs, MultiHance increases the signal inten- sity on T1-weighted MR sequences by shortening the T1 relaxation time. The extent to which a contrast agent is able to shorten the T1 relaxation time is a reflection of its r1 relaxivity. For most GBCAs the r1 relaxivity at 1.5T in vivo lies in the range between approximately 3.6 and 4.7 L/mmol/sec [10-12]. MultiHance differs from all other GBCAs approved for CNS imaging in that a lipophilic benzyloxymethyl substituent on the Gd-BOPTA – con- trast effective molecule interacts weakly and transiently with serum albumin [13, 14]. These interactions cause a slowing of the molecular tumbling rate of the molecule which results in considerably higher r1 relaxivity (6.3–7.9 L/mmo/sec) and thus greater shortening of the T1 relax- ation time relative to other agents. The impact of the
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