Atormac
Neurology India
menu-bar5 Open access journal indexed with Index Medicus
  Users online: 3996  
 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
 »Related articles
  »  Article in PDF (1,413 KB)
  »  Citation Manager
  »  Access Statistics
  »  Reader Comments
  »  Email Alert *
  »  Add to My List *
* Registration required (free)  

 
  In this Article
 »  Abstract
 »  Materials and Me...
 » Results
 » Discussion
 » Conclusions
 »  References
 »  Article Figures
 »  Article Tables

 Article Access Statistics
    Viewed2688    
    Printed77    
    Emailed0    
    PDF Downloaded125    
    Comments [Add]    

Recommend this journal

 


 
Table of Contents    
ORIGINAL ARTICLE
Year : 2017  |  Volume : 65  |  Issue : 5  |  Page : 1046-1052

Perfusion MR imaging of enhancing brain tumors: Comparison of arterial spin labeling technique with dynamic susceptibility contrast technique


1 Department of Radiodiagnosis, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
2 Department of Radiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
3 Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

Date of Web Publication6-Sep-2017

Correspondence Address:
Neetu Soni
Department of Radiodiagnosis, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226 014, Uttar Pradesh
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/neuroindia.NI_871_16

Rights and Permissions

 » Abstract 

Objective: Arterial spin labeling (ASL) magnetic resonance (MR) perfusion is a noninvasive and repeatable method for quantitatively measuring cerebral blood flow (CBF). This study aims to compare measurements of ASL-derived CBF with dynamic susceptibility contrast (DSC) MRI in the assessment of enhancing brain tumors (primary and metastatic), with an aim to use ASL as an alternative to DSC.
Materials and Methods: Thirty patients with newly diagnosed brain tumors (16 meningiomas, 6 gliomas, 3 metastases, 2 cerebellopontine angle schwannoma, 1 central neurocytoma, and 2 low-grade gliomas) were examined using a 3T MR scanner. Values of CBF, regional cerebral blood flow (rCBF), and regional cerebral blood volume (rCBV) were determined in the tumor (T) as well as in the contralateral normal gray matter (GM) and white matter (WM). Tumor-to-GM or WM CBF, rCBF, and rCBV ratios were calculated to estimate normalized perfusion values (i.e., ASL normalized tumor blood flow [nTBF], DSC nTBF, and DSC normalized tumor blood volume [nTBV]) from the ASL and DSC techniques. ASL and DSC MRI derived perfusion parameters were compared using paired t-test and correlated using Pearson correlation coefficient.
Results: Mean values for ASL nTBF and DSC nTBF using contralateral GM as the reference point were 2.98 ± 1.67and 2.91 ± 1.43, respectively. A very strong correlation coefficient was found between ASL nTBF and DSC nTBF with contralateral GM as the reference region (r = 0.903; R2= 0.813). Mean DSC nTBF and DSC nTBV also showed strong correlation (r = 0.83; R2= 0.701).
Conclusion: Our study results suggested that measurement of CBF from ASL possesses the potential for a noninvasive assessment of blood flow in intracranial tumors as an alternate to DSC MRI, in those patients requiring multiple follow-up imaging and in patients with impaired renal functions.


Keywords: Brain tumor imaging, dynamic susceptibility contrast, magnetic resonance imaging, normalized tumor blood flow, normalized tumor blood volume, pseudo-continuous arterial spin labeling
Key Message:
Non-invasive estimation of blood flow of intracranial tumors may be carried out by arterial spin labeling (ASL). This may serve as an alternative technique to dynamic susceptibility contrast (DSC) magnetic resonance imaging, especially in those subjects who require multiple follow up imaging and those with impaired renal functions, since an exogenously administered gadolinium contrast administration is not required in the former technique. However, the images obtained by the ASL technique are of lower resolution and take a longer acquisition time than those obtained by the DSC technique.


How to cite this article:
Soni N, Dhanota DS, Kumar S, Jaiswal AK, Srivastava AK. Perfusion MR imaging of enhancing brain tumors: Comparison of arterial spin labeling technique with dynamic susceptibility contrast technique. Neurol India 2017;65:1046-52

How to cite this URL:
Soni N, Dhanota DS, Kumar S, Jaiswal AK, Srivastava AK. Perfusion MR imaging of enhancing brain tumors: Comparison of arterial spin labeling technique with dynamic susceptibility contrast technique. Neurol India [serial online] 2017 [cited 2019 Oct 17];65:1046-52. Available from: http://www.neurologyindia.com/text.asp?2017/65/5/1046/214093


The two most common methods of magnetic resonance imaging (MRI) used for measuring brain perfusion are dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL), with more extensive clinical experience existing for DSC perfusion MRI. Perfusion MRI estimates tumor neoangiogenesis, which helps in tumor grading, guiding stereotactic biopsy, surgical planning, differentiating radiation necrosis from recurrent tumor, and assessing therapeutic response in clinical trials of new anti-angiogenic agents.[1],[2],[3],[4],[5] Both DSC and ASL perfusion MRI have been compared in various studies of brain tumors.[2],[6],[7],[8],[9],[10],[11],[12]

ASL technique was first reported by Deter et al.,[13] who provided absolute quantification of CBF using magnetically-labeled blood-water as an endogenous tracer, which makes ASL a promising technique for studying perfusion in patients with renal failure and in those who require repetitive follow-ups. Recently developed three-dimensional pseudo-continuous arterial spin labeling (3D PCASL) sequence, incorporating high-field, parallel imaging with background suppression, provides increased sensitivity.[1] These features may move ASL from the research stage towards clinical usage.[9] DSC-MRI based on T2-weighted imaging measures perfusion using an exogenous contrast agent. Comparative studies between ASL and DSC-MRI have found a close linear correlation between these two perfusion techniques.[2],[6],[7],[8],[12],[14],[15] The present study was conducted to compare the role of perfusion parameters obtained from ASL and DSC perfusion MRI in enhancing brain tumors (primary and metastatic) detected on the conventional MRI in our set of population, and to assess the feasibility of using ASL as an alternative to DSC.


 » Materials and Methods Top


Patient population

Thirty patients (age range = 19–71 years; 16 male and 14 female patients) with newly diagnosed enhancing brain tumors (primary and metastatic) were enrolled in this institutional ethics committee (IEC)-approved prospective study (July 2013 to September 2014). Informed consent was obtained from each patient prior to their undergoing the perfusion MRI. Patients with nonenhancing lesions, previous surgical interventions, and imaging with susceptibility artifacts that affects evaluation, were excluded from the study. The final diagnosis of the patients was obtained based on the clinical background, histopathology (after acquiring the perfusion MRI), and follow-up.

Magnetic resonance imaging acquisition

MRI was performed on a 3T MR scanner (Signa HDxt, General Electric, Milwaukee, USA) with a 16-channel head-neck-spine coil. The lesions were evaluated with conventional imaging using routine axial T2/T1-weighted, fluid-attenuated inversion recovery (FLAIR), diffusion-weighted imaging (DWI) sequences including 3D PCASL (combining pseudo continuous arterial spin labeling [PCASL], and three dimensional [3D] fast spin echo encoding and spiral trajectory acquisition techniques), and DSC perfusion MRI followed by postcontrast axial T1-weighted and 3D BRAVO (brain volume) sequences with same planning of DSC and ASL, respectively, to overlay CBF, and relative cerebral blood volume (rCBV) perfusion maps. Acquisition parameters for the 3D PCASL are described in our previous article by Soni et al.[16] DSC-MRI, a gradient echo EPI (echo planar imaging) sequence, was performed with the following parameters: TR = 2s/TE = 20.2 ms/slices = 20/slice thickness = 6 mm/spacing = 0/matrix = 128 × 96/average = 1/FOV = 24 cm × 24 cm/bandwidth = 62.5 kHz/scan time = 1 min 20s/axial plane. A series of 42 such scans were obtained at 1 s/image during the first pass of dynamic intravenous administration of gadolinium-DTPA (0.1 mmol/kg) at a rate of 3–5 ml/s followed by 20 ml saline flush at the same rate.

Image processing and data analysis

Post processing of ASL and DSC data was performed on ADW4.4 GE workstation using Functool 3D ASL and Brain stat Software to obtain color-coded CBF, rCBF, and rCBV maps, respectively, from each patient [Figure 1]. At least 3 regions of interest (ROIs) of 4–7 mm 2 were drawn over the tumor region showing the highest perfusion value in the CBF, rCBV, and rCBF maps, avoiding the regions of vessels, calcification, hemorrhage, cyst, and necrosis [Figure 2].
Figure 1: ROI was placed in the colored portion of the tumor showing the highest perfusion values in a similar manner and at the same region of the tumor in both DSC (a) and ASL (b) perfusion maps

Click here to view
Figure 2: ASL perfusion map (a), overlapped 3D BRAVO image (b) shows placement of ROIs at the normal gray matter (ROI 1), white matter (ROI 2) and tumor (ROI 3). Normalization was done by dividing the average tumor blood flow (ROI 3) by gray matter cerebral blood flow (ROI 1) and white matter cerebral blood flow (ROI 2) separately

Click here to view


For normalization, to avoid age and patient dependent CBF variations,

ROIs were placed in the the contralateral normal appearing frontal GM and periventricular WM [Figure 2]. The 3 ROI values were averaged to obtain the mean. The mean value of tumor ROI was divided by the mean value of contralateral normal GM and WM ROI to estimate normalized nTBF and nTBV values based on the CBF and rCBV maps.

Statistical analysis

ASL nTBF was compared with DSC nTBF values using paired t-test. Linear regression and Pearson's correlation were employed to examine the correlation between DSC and ASL-derived CBF values in tumor as well as normal GM and WM region. These statistical analyses were performed using the SPSS, version 16.0 software package (SPSS Inc., Chicago, IL, USA).


 » Results Top


All the patients recruited had a newly detected tumor and had not undergone any prior treatment. Tissue for histological analysis had been obtained at biopsy or during surgical resection of the tumor, and revealed 16 meningiomas, 6 gliomas, 3 metastases, 2 cerebellopontine angle schwannomas, and 1 central neurocytoma. Two patients did not undergo a histopathological examination; however, they had the characteristic MR features of a low-grade glioma and are on regular follow up.

Quantitative normalized perfusion value measurements

Quantitative perfusion values normalized to GM and WM (i.e., ASL nTBF, DSC nTBF, and DSC nTBV) as reference region were obtained in all 30 tumors [Table 1] and [Table 2]. Distribution of ASL nTBF, DSC nTBF, and DSC nTBV showed the highest values for meningiomas and the lowest values for gliomas among all the tumors [Table 3] and [Figure 3].
Table 1: Results of the perfusion MRI (ASLnTBF, DSCnTBF and DSCnTBV) normalised to GM and WM in all 30 tumour patients

Click here to view
Table 2: Quantitative normalized tumour perfusion values (mean±S.D) in ASL and DSC in all tumours

Click here to view
Table 3: Quantitative normalized perfusion values (mean±S.D) with GM as reference region in gliomas and non gliomas/meningiomas and non meningiomas

Click here to view
Figure 3: Boxplot showing ASL (ASL nTBF) and DSC MRI (DSC nTBF and nTBV) values normalized to GM in different tumor types

Click here to view


Pearson's correlation coefficient between ASL and DSC normalized perfusion values

A highly strong correlation coefficient between ASL nTBF and DSC nTBF was found in all 30 tumors when normalized to GM [Figure 4] rather than to WM as the reference region [Table 4], with the highest correlation being seen in gliomas. Similarly, correlation coefficient for DSC nTBF and DSC nTBV was also calculated and found to be high (r = 0.83 with R2= 0.701) when normalized to GM. Our study results support that PCASL could be used as an alternative to DSC-MRI in non-invasively estimating the in vivo intracranial tumor blood flow.
Figure 4: Scatter plot diagram showing correlation between ASL nTBF and DSC nTBF, normalized to gray matter (a) and white matter (b) in all 30 brain tumor patients. The line represents linear regression between ASL nTBF and DSC nTBF with the Pearson correlation coefficient of r = 0.902 and r = 0.732, respectively. (c) Similarly, the Pearson correlation coefficient between DSC nTBF and nTBV was r = 0.83 normalized to gray matter

Click here to view
Table 4: Pearson's correlation coefficient for ASL nTBF and DSC nTBFs

Click here to view


The mean ASL absolute tumor blood flow (TBF) values were also calculated among all tumors and subtypes [Table 5]. Similarly, the mean of normal absolute ASL CBF values were calculated for normal GM and WM separately in all 30 patients [Table 5].
Table 5: Absolute ASL TBF values (mean±S.D) in different tumour subtypes and from normal GM and WM

Click here to view



 » Discussion Top


The purpose of this study was to quantitatively compare perfusion values from ASL with DSC MRI in brain tumors, with an aim to evaluate the usage of ASL as an alternative to DSC in routine clinical and research studies. In routine clinical practice, brain tumor perfusion is mainly calculated from rCBF and rCBV perfusion maps using DSC MRI. ASL is a relatively new, evolving technique for clinical and research studies. The types of contrast agents (exogenous gadolinium-based contrast agent in DSC MRI and endogenous tracer in the ASL technique) and the post-processing algorithm used in these two perfusion techniques provide different perfusion values.[7],[12],[17],[18],[19] DSC-MRI is based on T2-weighted imaging and requires a faster dynamic echo-planar imaging scan with parallel imaging to cover the whole brain.[19],[20] ASL provides absolute CBF values, which is difficult with DSC MRI because of a careful selection of arterial input function (AIF) and advanced post-processing deconvolutional algorithms.[21] ASL was, therefore, quantitatively compared with DSC MRI by means of normalized perfusion values in this study. Our study demonstrated evidence that supported a close linear correlation between normalized perfusion values derived from ASL and DSC [Figure 4], and the results are consistent with previous studies [Table 6].[2],[7],[8],[22]
Table 6: Correlation coefficient values (r) in studies comparing ASL and DSC techniques

Click here to view


The correlation coefficient value in our study is in close approximation with the study done by Van Westen et al., where GM was used as the reference region for normalization.[22] The slight difference which is seen when we compared our results with that of other studies may be due to reference region choice and tumor composition. Our ASL nTBF and DSC nTBF values normalized to WM showed a weak correlation [Figure 4]. Underestimation of WM CBF by ASL due to the long transit times and higher water content of the normal contralateral white matter in brain tumors make WM a questionable reference region.[9],[23],[24]

Most previous MRI studies performed DSC nTBV for the evaluation of brain tumor perfusion and showed a diagnostic comparison with CBF.[9],[12],[18],[19],[25] As seen in the previous studies, a strong correlation was seen between DSC nTBF and DSC nTBV (r = 0.837) [Figure 4], supporting the fact that DSC nTBF may be as good as DSC nTBV for the assessment of brain tumor perfusion.[7] Ata et al.,[12] also reported a strong correlation (r = 0.91, P> 0.001) in the comparison of relative regional DSC rCBF and rCBV values.

Correlation coefficient in gliomas was reported to be stronger than meningiomas [0.98 vs 0.814]. Although the sample size of gliomas in our study was small (n = 8), nTBF ASL and nTBF DSC values lie in the range that were similar to the findings of the previous studies [Table 7]. The slight difference from the other studies could be mainly due to a higher number of patients with a high-grade gliomas recruited by them. In our study, among all the tumors, meningiomas have shown the highest ASL nTBF (3.7 ± 1.63) and absolute ASL TBF (177 ± 89.2 ml/min/100 g) values, which is in agreement with a previously published study [Table 3] and [Table 5].[22] Thus, our study results indicate that ASL can be used as an alternative to DSC.
Table 7: Normalised TBF values (mean,±S.D) in gliomas (both high grade [HG] and low grade [LG]), results of previous studies compared with present study

Click here to view


Similar good correlation has been reported for overall brain tumors in a few recent studies.[2],[6],[7],[8],[9],[10],[11],[12] Close linear correlation (r = 0.83; P<.005) was found by Warmuth et al.,[2] between ASL and DSC in histologically proved brain tumors. Weber et al.,[6] suggested that ASL and DSC MRI techniques determining rCBF in brain metastasis after stereotactic radiosurgery allow prediction of the treatment outcome with equal confidence. Jarnum et al.,[7] also found a good correlation between the normalized ASL and DSC nTBF values (r = 0.82) in 28 enhancing brain tumors. Similarly, Lehmann et al.,[8] analyzed patients of gliomas, metastases, and meningiomas with ASL and DSC MRI sequences, and concluded that ASL is a good alternative to DSC MRI. Other recent studies, have also found a good correlation between ASL and DSC techniques, and suggested that ASL perfusion can be used in clinical practice.[9],[10],[11],[12] More recently, Ata et al.,[12] also reported a strong correlation (r = 0.86) with a high sensitivity and specificity between DSC and multiphase ASL in 27 brain tumor patients. In general, most of the studies support the opinion that ASL could be a noninvasive alternative to DSC.

ASL offers several advantages over DSC due to its noninvasive nature, simple post-processing, no exogenous contrast use, being safe in patients with impaired renal function, and having the ability to provide quantitative tissue perfusion. This renders ASL an ideal technique for routine clinical and research studies. Certain pathological conditions severely impair the blood–brain barrier and result in extravascular contrast agent leakage, which results in miscalculation of the DSC perfusion mapping. There are a few limitations of ASL, such as generating only the CBF perfusion map, which are of relatively lower resolution and takes a longer acquisition time than the DSC perfusion map.[1],[12]

Limitation

Although data from our current study is encouraging, the study included a small number of patients, especially those with a high or a low-grade glioma, and patients with metastases.


 » Conclusions Top


This study has shown a very strong correlation between 3D PCASL and DSC MRI perfusion values and support the possibility of ASL being used as an alternative to DSC MRI for the evaluation of brain tumors. Nowadays, with the more extensive use of 3T scanners, improved ASL perfusion sequences with whole brain coverage, low cost, safety in impaired renal function, easy availability, and simple quantification are possible to execute. The ASL method can be introduced in everyday clinical practice and has a wide range of applications including the monitoring and follow-up of brain tumors while avoiding the requirement of repeated contrast injections.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
 » References Top

1.
Wolf RL, Detre JA. Clinical neuroimaging using arterial spin-labeled perfusion magnetic resonance imaging. Neurotherapeutics 2007;4:346-59.  Back to cited text no. 1
    
2.
Warmuth C, Gunther M, Zimmer C. Quantification of blood flow in brain tumors: Comparison of arterial spin labeling and dynamic susceptibility-weighted contrast-enhanced MR imaging. Radiology 2003;228:523-32.  Back to cited text no. 2
    
3.
Wolf RL, Wang JJ, Wang SM, Melhem ER, O'Rourke DM, Judy KD, et al. Grading of CNS neoplasms using continuous arterial spin labeled perfusion MR imaging at 3 tesla. J Magn Reson Imaging 2005;22:475-82.  Back to cited text no. 3
    
4.
Lev MH, Rosen BR. Clinical applications of intracranial perfusion MR imaging. Am J Neuroradiol 1999;9:309-31.  Back to cited text no. 4
    
5.
Roberts HC, Roberts TPL, Brasch RC, Dillon WP. Quantitative measurement of microvascular permeability in human brain tumors achieved using dynamic contrast-enhanced MR imaging: Correlation with histologic grade. Am J Neuroradiol 2000;21:891-9.  Back to cited text no. 5
    
6.
Weber MA, Lichy MP, Thilmann C, Gunther M, Delorme S, Zuna I, et al. Assessment of irradiated brain metastases by means of arterial spin-labeling and dynamic susceptibility-weighted contrast-enhanced perfusion MRI: Initial results. Invest Radiol 2004;39:277-87.  Back to cited text no. 6
    
7.
Järnum H, Steffensen EG, Knutsson L, Günther M, Delorme S, Zuna I, et al. Perfusion MRI of brain tumours: A comparative study of pseudo-continuous arterial spin labelling and dynamic susceptibility contrast imaging. Neuroradiology 2010;52:307-17.  Back to cited text no. 7
    
8.
Lehmann P, Monet P, Marco G, Saliou G, Perrin M, Stoquart-Elsankari S, et al. A comparative study of perfusion measurement in brain tumours at 3 Tesla MR: Arterial spin labeling versus dynamic susceptibility contrast-enhanced MRI. Eur Neurol 2010;64:21-6.  Back to cited text no. 8
    
9.
Knutsson L, van Westen D, Petersen ET, Bloch KM, Holtås S, Ståhlberg F, et al. Absolute quantification of cerebral blood flow: Correlation between dynamic susceptibility contrast MRI and model-free arterial spin labeling, Magn Reson Imaging 2010;28:1-7.  Back to cited text no. 9
    
10.
White CM, Pope WB, Zaw T, Qiao J, Naeini KM, Lai A, et al. Regional and voxel-wise comparisons of blood flow measurements between dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) and arterial spin labeling (ASL) in brain tumors. J. Neuroimaging 2014;24:23-30.  Back to cited text no. 10
    
11.
Jiang J, Zhao L, Zhang Y, Zhang S, Yao Y, Qin Y, et al. Comparative analysis of arterial spin labeling and dynamic susceptibility contrast perfusion imaging for quantitative perfusion. Int J Clin Exp Pathol 2014;15:2790-9.  Back to cited text no. 11
    
12.
Ata ES, Turgut M, Eraslan C, Dayanir YO. Comparison between dynamic susceptibility contrast magnetic resonance imaging and arterial spin labelling techniques in distinguishing malignant from benign brain tumors. Eur J Radiol 2016;85:1545-53.  Back to cited text no. 12
    
13.
Detre JA, Leigh JS, Williams DS, Koretsky AP. Perfusion imaging. Magn Reson Med 1992;23:37-45.  Back to cited text no. 13
    
14.
Kimura H, Takeuchi H, Koshimoto Y, Arishima H, Uematsu H, Kawamura Y, et al., Perfusion imaging of meningioma by using continuous arterial spin-labeling: Comparison with dynamic susceptibility-weighted contrast-enhanced MR images and histopatologic features. AJNR Am J Neuroradiol 2006;27:85-93.  Back to cited text no. 14
    
15.
Ozsunar Y, Mullins ME, Kwong K, Hochberg FH, Ament C, Schaefer PW, et al. Glioma recurrence versus radiation necrosis? A pilot comparison of arterial spin labeled, dynamic susceptibility contrast enhanced MRI and FDG-PET imaging. Acad Radiol 2010;17:282-90.  Back to cited text no. 15
    
16.
Soni N, Jain A, Kumar S, Pandey CM, Awasthi A. Arterial spin labeling magnetic resonance perfusion study to evaluate the effects of age and gender on normal cerebral blood flow. Neurol India 2016;64:S32-8.  Back to cited text no. 16
    
17.
Spampinato MV, Smith JK, Kwock L, Ewend M, Grimme JD, Camacho DL, et al. Cerebral blood volume measurements and proton MR spectroscopy in grading of oligodendroglial tumors. AJR Am J Roentgenol 2007;188:204-12.  Back to cited text no. 17
    
18.
Shin JH, Lee HK, Kwun BD, Kim JS, Kang W, Choi CG, et al. Using relative cerebral blood flow and volume to evaluate the histopathologic grade of cerebral gliomas: Preliminary results. AJR Am J Roentgenol 2002;179:783-89.  Back to cited text no. 18
    
19.
Knutsson L, Stahlberg F, Wirestam R. Aspects on the accuracy of cerebral perfusion parameters obtained by dynamic susceptibility contrast MRI: A simulation study. Magn Reson Imaging 2004;22:789-98.  Back to cited text no. 19
    
20.
Griswold MA, Jakob PM, Heidemann RM, Nittka M, Jellus V, Wang J, et al. Generalized autocalibrating partially parallel acquisitions. Magn Reson Med 2002;47:1202-10.  Back to cited text no. 20
    
21.
Petersen ET, Zimine I, Ho YC, Golay X. Non-invasive measurement of perfusion: A critical review of arterial spin labelling techniques. Br J Radiol 2006;79:688-701.  Back to cited text no. 21
    
22.
Van Westen D, Knutsson L, Petersen E T, Bloch KM, Ståhlberg F. Comparison of arterial blood volume obtained from model-free arterial spin labelling (ASL) and cerebral blood volume obtained from contrast enhanced dynamic susceptibility weighted imaging (DSC) in brain tumours. Magn Reson Imaging 2006;55:219-32.  Back to cited text no. 22
    
23.
Andersen C. In vivo estimation of water content in cerebral white matter of brain tumour patients and normal individuals: Towards a quantitative brain oedema definition. Acta Neurochir 1997;139:249-55.  Back to cited text no. 23
    
24.
Alsop DC, Detre JA. Reduced transit-time sensitivity in noninvasive magnetic resonance imaging of human cerebral blood flow. J Cereb Blood Flow Metab 1996;16:1236-49.  Back to cited text no. 24
    
25.
Jenkinson MD, Smith TS, Joyce KA, Fildes D, Broome J, du Plessis DG, et al. Cerebral blood volume, genotype and chemosensitivity in oligodendroglial tumours. Neuroradiology 2006;48:703-13.  Back to cited text no. 25
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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