Leveron&Nexovas
Neurology India
menu-bar5 Open access journal indexed with Index Medicus
  Users online: 4849  
 Home | Login 
About Editorial board Articlesmenu-bullet NSI Publicationsmenu-bullet Search Instructions Online Submission Subscribe Videos Etcetera Contact
  Navigate Here 
 Search
 
  
 Resource Links
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
    Article in PDF (397 KB)
    Citation Manager
    Access Statistics
    Reader Comments
    Email Alert *
    Add to My List *
* Registration required (free)  

 
  In this Article
   Diffusion-weight...
   Diffusion-weight...
   Susceptibility-w...
   Magnetic resonan...
   Perfusion-weight...
   References

 Article Access Statistics
    Viewed2783    
    Printed46    
    Emailed0    
    PDF Downloaded74    
    Comments [Add]    

Recommend this journal

 


 
Table of Contents    
THE EDITORIAL DEBATE
Year : 2015  |  Volume : 63  |  Issue : 4  |  Page : 481-482

Brain tumor magnetic resonance imaging - so near yet so far


Department of Radiology, Indraprastha Apollo Hospitals, New Delhi, India

Date of Web Publication4-Aug-2015

Correspondence Address:
Harsh Rastogi
Department of Radiology, Indraprastha Apollo Hospitals, New Delhi
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.161981

Rights and Permissions



How to cite this article:
Rastogi H, Kumar P. Brain tumor magnetic resonance imaging - so near yet so far. Neurol India 2015;63:481-2

How to cite this URL:
Rastogi H, Kumar P. Brain tumor magnetic resonance imaging - so near yet so far. Neurol India [serial online] 2015 [cited 2022 May 19];63:481-2. Available from: https://www.neurologyindia.com/text.asp?2015/63/4/481/161981


Ever since its introduction in clinical practice, magnetic resonance imaging (MRI) of brain tumors has evolved by leaps and bounds. Its clinical utility, based on the information provided, has undergone a significant change especially in the last decade. Earlier, it revealed only the intimate anatomic details vis-à-vis the surrounding neurovascular structures; however, now it also provides information regarding the tumor's metabolism and physiology through MR spectroscopy (MRS), diffusion-weighted images and apparent diffusion coefficient maps image (DWI and ADC), and perfusion-weighted imaging (PWI) and susceptibility-weighted imaging (SWI). [1],[2],[3]

Using these newer techniques, Zhao et al. have developed a new method to classify pathologic low/high grades of astrocytomas. [4] They found ADC, MRS, DWI and PWI along with conventional MRI very helpful in differentiating the two entities.


  Diffusion-weighted images/apparent diffusion coefficient Top


DWI evaluates water diffusivity. A highly cellular tumor will have less extracellular space, restricting diffusion of water molecules in this space. These restricted water molecules lose lesser amount of signal and appear hyperintense on DWI sequence. In clinical practice, we also use what is called ADC maps, which is an absolute measure of the average diffusion for each voxel. [5] Several studies have shown an inverse relationship between a glioma's grade and its ADC. A high-grade glioma has a proportionately lower ADC. [6] Yet, its clinical usage needs investigation. This is because of several factors such as heterogeneity within the tumor and the presence/absence of hemorrhage/calcification in the tumor or in its close vicinity.


  Diffusion-weighted images/diffusion tensor imaging Top


Another useful application of multidirectional DWI is to ascertain diffusion's directionality and magnitude, especially along the white matter tracts. This is known as diffusion tensor imaging, which at times is of immense use in planning the surgical approach.


  Susceptibility-weighted imaging Top


Zhang et al. found that contrast-enhanced SWI was better than the conventional contrast-enhanced T1-weighted imaging in visualizing small tumor vessels. A high-grade astrocytoma shows increased tumor vascularity and larger areas of micro-hemorrhage. Low-grade tumors conversely have smaller areas of micro-hemorrhages and a "sparse" vessel density. [3]


  Magnetic resonance spectroscopy Top


1 H-MRS (proton spectroscopy) provides insights into the metabolic changes at the cellular level. A number of metabolites can be mapped, some of which can also act as biomarkers and provide information about the tumor's biology. [1]

Common metabolites thus evaluated are:

  • N-acetyl aspartate - Present in neurons (its value is diminished in tumors)
  • Choline (Cho) - A surrogate marker for cell membrane synthesis (with a corresponding high value in tumors)
  • Creatine (Cr) - Represents an energy cycle (metabolic activity)
  • Lactate (Lac) - An end product of nonoxidative glycolysis. A marker for hypoxia in the tumor tissue
  • Lipid (Lip) - Moieties denote necrosis
  • Myo-inositol - A marker of mature glial cells that is raised in Grade II glioma.



  Perfusion-weighted imaging Top


It is carried out to assess the neo-angiogenesis and capillary permeability. These help to grade the degree of malignancy and prognosis, particularly in gliomas. Perfusion has also been used to differentiate a tumor from a nontumoral lesion and also to differentiate a primary from a secondary tumor. [1] It can also be used to determine the most appropriate site within the tumor to take a biopsy from (degree of perfusion correlates directly with the grade of the tumor). It is also used to assess the response to treatment (such as radiotherapy), recurrence and malignant transformation of the tumor. There are three commonly used techniques for perfusion imaging.

  1. Dynamic susceptibility-weighted contrast-enhanced imaging [1] - it is a T2 * technique using a contrast medium. It is the most commonly used technique where relative cerebral blood volume (rCBV) derived from the area under the susceptibility time intensity curve represents angiogenesis in brain tumors. Grade of an astrocytoma correlates very well with the rCBV values. A high value of rCBV is seen in high-grade gliomas, which implies a poorer prognosis. This, however, does not apply to oligodendrogliomas, which may have elevated rCBV even though the tumor is of low grade.
  2. Arterial spin labeling - it does not use any contrast medium. Its clinical use is currently very limited.
  3. Dynamic contrast-enhanced imaging (DCE) [1] - A T1-weighted contrast-enhanced perfusion technique. Proponents of DCE perfusion technique have found a strong correlation between microvascular permeability and tumor grade. [7]


Hu et al. in their paper titled "Feasibility of tissue similarity map (TSM)-based rCBV in the evaluation of gliomas" found that TSM-based rCBV can accurately differentiate between high-grade and low-grade gliomas due to an improved signal-to-noise ratio. TSM depends only on the signal intensity curve. [8]

MR perfusion studies have now become an integral part of the standard protocol of brain tumor analysis; they have positively impacted the management decisions taken by the multidisciplinary treating team of a neurosurgeon, a neuroradiologist and a radiotherapist. [9]

These newer MRI techniques can provide answer to many clinical problems such as:

  • Differentiating a brain tumor from an abscess and demyelination
  • Differentiating a primary from a secondary tumor
  • Identifying the appropriate site for taking a biopsy
  • Identifying the type of primary neoplasm
  • Grading the primary neoplasm
  • Assessing the response to treatment - necrosis, recurrence or malignant transformation
  • Differentiating radiation changes from recurrence.


Even though these MR techniques have been able to answer these questions, they still have their own limitations. However, the way scientific knowledge and technology are advancing, it is quite possible that we may, in the near future, be able to provide diagnosis that may be equivalent to a histopathological examination of the tumors.

 
  References Top

1.
Cha S. Update on brain tumor imaging: From anatomy to physiology. AJNR Am J Neuroradiol 2006;27:475-87.  Back to cited text no. 1
    
2.
Mohindra N, Neyaz Z. Magnetic resonance sequences: Practical neurological applications. Neurol India 2015;63:241-9.  Back to cited text no. 2
[PUBMED]  Medknow Journal  
3.
Zhang H, Tan Y, Wang XC, Qing JB, Wang L, Wu XF, et al. Susceptibility-weighted imaging: The value in cerebral astrocytomas grading. Neurol India 2013;61:389-95.  Back to cited text no. 3
[PUBMED]  Medknow Journal  
4.
Zhao ZX, Lan K, Xiao JH, Zhang Y, Xu P, Jia L, et al. A new method to classify pathologic grades of astrocytomas based on magnetic resonance imaging appearances. Neurol India 2010;58:685-90.  Back to cited text no. 4
[PUBMED]  Medknow Journal  
5.
Le Bihan D. Apparent diffusion coefficient and beyond: What diffusion MR imaging can tell us about tissue structure. Radiology 2013;268:318-22.  Back to cited text no. 5
    
6.
Yamasaki F, Kurisu K, Satoh K, Arita K, Sugiyama K, Ohtaki M, et al. Apparent diffusion coefficient of human brain tumors at MR imaging. Radiology 2005;235:985-91.  Back to cited text no. 6
    
7.
Roberts HC, Roberts TP, Brasch RC, Dillon WP. Quantitative measurement of microvascular permeability in human brain tumors achieved using dynamic contrast-enhanced MR imaging: Correlation with histologic grade. AJNR Am J Neuroradiol 2000;21:891-9.  Back to cited text no. 7
    
8.
Hu C, Hu S, Gao X, Sun C, Gan W, Liu Y, et al. Feasibility of tissue similarity map (TSM) based relative cerebral blood volume (rCBV) in the evaluation of gliomas. Neurol India 2015;63:525-31.  Back to cited text no. 8
    
9.
Geer CP, Simonds J, Anvery A, Chen MY, Burdette JH, Zapadka ME, et al. Does MR perfusion imaging impact management decisions for patients with brain tumors? A prospective study. AJNR Am J Neuroradiol 2012;33:556-62.  Back to cited text no. 9
    




 

Top
Print this article  Email this article
   
Online since 20th March '04
Published by Wolters Kluwer - Medknow