PHYSIOLOGICAL MR IMAGING

Q.All are true regarding tumour except
a. WHO grade II oligodendrogliomas have significantly higher rCBV than WHO grade II astrocytomas
b. rCBV measurements significantly increased the sensitivity and positive predictive value of conventional MR imaging in glioma grading
c. In radiation necrosis, the enhancing lesion has a lower  rCBV than recurrent tumour
d. ADC measurements of the enhancing components in recurrent tumour are significantly lower than in radiation necrosis
e. peritumoural regions in metastases  show  increase in rCBV or decrease in FA


ANS.----e

The peritumoural regions of high-grade gliomas show a more marked decrease in ADC, fractional anisotropy and NAA and increase in rCBV compared to low-grade tumours. This is a reflection of the more invasive nature of these tumours, which infiltrate the adjacent brain tissue along vascular channels, leading to an rCBV increase; destroy ultrastructural boundaries with a consequent decrease in ADC and FA; and replace normal brain tissue, resulting in a drop of NAA. Metastases on the other hand are surrounded by ‘pure’ vasogenic oedema, which contains no infiltrating tumour cells. These peritumoural regions in metastases therefore show no increase in rCBV or decrease in FA.

Xe ?

Q.All are true regarding Xenon computed tomography  except

a. xenon is freely diffusable and penetrates the blood–brain barrier

b. Xenon computed tomography  can be used to assess cerebral blood perfusion

c. The washout of xenon occurs relatively slowly

d. patient movement during  period of imaging causes misregistration of data

e. patient inhale  of a gas containing 28 per cent xenon

ANS ---c

The washout of xenon occurs relatively rapidly, allowing a repeat examination after 15–20 min.

SIMPLE BUT USEFUL

Q.The size of circle of Willis aneurysms  that can be detected in most of cases  by intracranial MRA  by  state-of-the-art acquisition and postprocessing methodology
a.>2mm
b. >3mm
c. >4mm
d. >5mm
e. >6mm


ANS.---b