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

HAPPY HOLI

Everyone' s "Girl friend" of Radiology ------

Common Findings in Tuberous Sclerosis

Brain    Cortical tubers    Subependymal nodules (“candle gutterings”)    Ventriculomegaly (“idiopathic or obstructive”)    Redial-glia abnormalities    Subependymal giant cell astrocytoma    Seizures    Infantile spasms (hypsarrhythmia)    Mental handicap Eye    Retinal hamartoma (phakoma of van der Hoeve) Skin    Angiofibroma (of face) (“angiofibroma”)    Ungual fibroma (angiofibroma of nailbed)    Hypomelanotic macules (ash leaf macule)    Shagreen patch (subepidermal fibrosis)    Fibrous forehead plaque Heart    Cardiac rhabdomyoma Kidney    Multiple angiomyolipoma    Multiple cysts Lung    Lymphangiomyomatosis    “Honeycomb lung”    Pheumothorax Bone    Bone islands (sclerotic calvarial patches) “Cystic” bone lucencies (small tubular bones—hands, etc.) Primary diagnostic criteria (only one necessary) are in italics. Many of the features not in italics are “secondary diagnostic criteria”—two or more of which and/or a family history can also be used to make a clinical diagnosis of the tuberous sclerosis complex.

INTRACRANIAL TUMOUR

Q.All are true regarding intracranial tumour except

a. Fat-containing neoplasms are  teratoma and dermoid

b. chemical shift artifact is big hurdle in detecting  presence of fat in tumour

c. Fat-selective suppression methods –useless in the distinction of etiologies of hyperintense tumors on T1W

d. Melanin in tumors is seen as high intensity on T1W and intermediate intensity on T2W

e. fat is hyperintense on T1W and intermediate intensity on conventional T2W

ANS.---c

Chemical shift artifact provides clue to the presence of fat in tumour. This artifact is displayed as a region of signal void at fat–water interfaces and hyperintensity at water–fat interfaces along the frequency-encoding axis . Fat-selective suppression methods  can play a role in the distinction of etiologies of hyperintense tumors on T1-weighted images.

?Spetzler and Martin

Q. All are true regarding AVM grading system (proposed by Spetzler and Martin)
a. higher grades lesions indicate  that lesions are more surgically difficult
b. evaluates  the size of the nidus, the location of the nidus, and the arterial feeders
c.“eloquent” areas AVMs is is given score of 1
d. large or diffuse AVMs encompassing the entirety of critical structures are classified as grade VI
e.  large AVMs with  eloquent cortex involvement , deep drainage belongs to grade V

ANS ---b
Spetzler and Martin grading of AVMs involves  evaluation of three features: the size of the nidus, the location of the nidus, and the venous drainage pattern.

? Chemical Exchange Saturation transfer (CEST) agent

Q.All are true regarding chemical exchange saturation transfer (CEST) agent except

a. make use of the phenomenon of magnetization transfer between water protons and protons in other molecules

b. used to detect endogenous species that are abundant in vivo, such as amide groups in tumors

c. offer unique approaches to obtaining MR contrast from physiologic changes such as pH

d. acquisition of two data sets is required

e. rely on the same principles of relaxation as simple paramagnetic ions

ANS .---e

CHEMICAL EXCHANGE AGENTS is a different class of contrast agents that does not rely on the same principles of relaxation as simple paramagnetic ions but instead make use of the phenomenon of magnetization transfer between water protons and protons in other molecules, such as in amide groups, which have a different resonant frequency. These so-called chemical exchange saturation transfer (CEST) agents produce contrast in appropriate imaging sequences as a result of magnetization transfer between water protons and protons in the agent that may dissociate and thereby undergo “chemical exchange.”

 By applying saturating radiofrequency energy at the precise frequency of the labile proton while it is chemically associated with the agent (which is different from the frequency of the solute water), one causes the MR signal from the water to decrease when the exchange occurs. The magnitude of the effect on the MR signal intensity depends strongly on the rate at which the protons exchange between the agent and the water. Moreover, the effect of the agent is visible only when the saturating RF pulse is applied to induce the effect.

In simple CEST experiments, acquisition of two data sets is required; in one, an RF pulse is applied at the frequency of the agent-bound proton, and in a second, the applied RF is set symmetrically on the other side of the water resonance. The signal from the first data set contains a combination of the CEST effect and direct saturation of the water, whereas the second acquisition measures only the latter. Subtraction of these two sets results in signal changes due to the CEST effect alone. CEST techniques have been used to detect endogenous species that are abundant in vivo, such as amide groups in tumors (36) and -OH groups in glycogen in perfused liver

Dynamic susceptibility contrast (DSC) MRI

Q. All are true regarding dynamic susceptibility contrast (DSC) MRI except

a. T2 and T2* are increased relative to normal physiologic value

b. the contrast agent is usually injected as a rapid bolus

c. images are acquired rapidly to monitor the signal change on time scales of 2 seconds or less

d. the tighter the bolus, the better

e.  rapid the transit time of contrast through the tissue is a big challenge of DSC MRI

ANS.---a

When contrast agent is present in high concentration in the vasculature, T2 and T2* are decreased relative to normal physiologic values. Smaller T2 or T2* means that the signal intensity on T2- and T2*-weighted images is decreased relative to normal

PROTECT PENUMBRA TO LOVE

Q.All are true regarding pathophysiology of stroke except

a. Normal cerebral blood flow is in the range of 50 to 55 mL/100 g brain tissue/min

b. cerebral blood flow values below 10 mL/100 g/min may lead to infarction within a matter of minutes

c. Cell depolarization is not observed until blood flow drops below 10 mL/100 g/min

d. penumbra surround the zone around the central core

e. In acute period there is a swelling and softening of the tissue with evidence of mass effect

ANS.----e

An initial acute period lasts for the first 2 days after the infarction in which gross examination demonstrates what appears to be normal tissue. This is followed by a subacute period during which there is a swelling and softening of the tissue with evidence of mass effect. This subacute period (with reference to pathology) generally extends for 7 to 10 days after the infarction, with maximal edema occurring at approximately 3 to 5 days. The chronic period extends from weeks to months after the infarction. During this time the infarcted tissue evolves into an area of encephalomalacia or cystic change.

Functionally the ischemic tissue can be divided into three compartments. The infarct core representing the dead or dying tissue is at the center of the infarction. The zone around the central core may have lost electrical activity, but it has more moderate reductions in blood flow and is defined as the penumbra. With reperfusion this tissue may be salvageable, but without reperfusion it may go on to infarction . Surrounding the penumbra is tissue with mildly reduced blood flow, often called the oligemic region. This tissue is more likely to survive; however, this region too may go on to infarct if perfusion is further hemodynamically altered.

WHAT IS ECCHORDOSIS?

Q.All are true regarding intracranial pathology except

a. Almost all cranial chordomas are found in relation to the clivus

b. Ecchordosis refers to a nodule of benign cells of notochordal origin

c. Pituicytoma and Granular Cell Tumors  is situated anteriorly  within the gland

d. Pituicytoma and Granular Cell Tumors  are extremely vascular

 e.chordomas are  histologically benign but locally invasive and destructive

ANS.---c

The most telling feature of  Pituicytoma and Granular Cell Tumors is its the specific anatomic site .In fact, the diagnosis of Pituicytoma and Granular Cell Tumors should be suspected when the pituitary mass is situated posteriorly within the gland and the normal posterior lobe hyperintensity cannot be identified. Of course, the most common posteriorly situated pituitary tumor is still the adenoma.

Ecchordosis refers to a nodule of benign cells of notochordal origin, usually the size of a pea, that occurs in or attached to the clivus . Although related to chordoma embryologically, ecchordosis differs from chordoma in that it is not a neoplasm and has no potential for growth or dissemination