stroke evolution

• Hyperacute: <6 hours: best described as cytotoxicoedema represented by the shift of waterin neurons. Because this is a relatively modest change, the CT in this stage is usually negative. On occasion, a CT scan obtainedin the hyperacute phase can give direct signs(e.g., vessel hyperdensity, subtle parenchymalhypodensity) or indirect signals (e.g., sulcaleffacement, gyral swelling, ventricular compression,fading of the white matter/grey matter interface)of hyperacute ischaemia. Such findingshave a negative prognostic value and are directlyassociated with the degree of neurological disability. Vessel hyperdensity in major cerebralarteries or one of their branches (the middlecerebral artery is the most commonly affected)can be observed within the first minutes following the onset of neurological signs andsymptoms and takes place before the appearanceof CT findings of the parenchymal infarct inthe corresponding territory. This increasein intravascular density, which is visible on CT without the use of contrast agents, appearsto be caused by the formation of an endoluminalclot, either by arterial thrombosis orembolism

Acute: – The acute phase of ischaemia occurs within the first 24 hours of the event, but typically begins within 6 hours after the stroke onset. From a neuropathological point of view, vasogenic oedema is present as supported by the filling of the extracellular spaces of the brain due to a blood-brain barrier breakdown. 

Subacute:  

24 hours after the event and continues until six weeks from the onset. From a neuropathological

point of view, beginning in the start of the second week there is an increase in   the vasogenic oedema as  in CT by an area with increasingly low attenuation coefficients, better defined margins and mass effect (internal cerebral herniations are possible,especially in cases of massive ischaemia) the ischaemic area appears most clearlytwo to three days after clinical onset of stroke.From the second week after the event, the oedemaand mass effect gradually subside and the area of hypodensity becomes less clear in some cases it disappears altogetherand the ischaemic area becomes difficultor impossible to distinguish from the normalbrain surrounding it. This is the so-called“fogging effect”, which is supported neuropathologicallyby an increase in cellularity dueto the invasion of microphages and the proliferation of capillaries 

Chronic: the chronic stage of ischaemiacoincides with the start of the sixth week from the onset of the clinical stroke and ischaracterized by repair processes. Parenchyma lhypodensity with well-defined marginsappears with attenuation values in the CSF range

Neuroradiology book

http://books.google.com/books?id=uH0R1SX7b0IC&printsec=frontcover&dq=neuroradiology&hl=en&ei=TSNoTt_AKoSCgAfQ0ezrDA&sa=X&oi=book_result&ct=result&resnum=5&sqi=2&ved=0CD4Q6AEwBA#v=onepage&q=stroke&f=false


http://books.google.com/books?id=bR6YTH1fycUC&printsec=frontcover&dq=neuroradiology&hl=en&ei=TSNoTt_AKoSCgAfQ0ezrDA&sa=X&oi=book_result&ct=result&resnum=6&sqi=2&ved=0CEQQ6AEwBQ#v=onepage&q&f=false

how to read brain MRI

http://www.med.wayne.edu/diagradiology/anatomy_modules/brain/brain.html

http://www.med.harvard.edu/aanlib/cases/caseNA/pb9.htm


https://www.msu.edu/~brains/brains/human/index.html

spinal stenosis

http://www.youtube.com/watch?v=WGY6GDJUBPY&NR=1

How to read Spine MRI

Cervical Spine MRI
http://www.youtube.com/watch?v=iyWEXDSt7xY&NR=1

http://www.youtube.com/watch?v=9n09uGsCEkA&NR=1
http://www.youtube.com/watch?v=SwNF_foFfAQ&feature=related

lumbar spine MRI
http://www.youtube.com/watch?v=C9LBdAwBVZg&feature=related
http://www.youtube.com/watch?v=PZqimf1DbcE&feature=related

MRI basics

What is MRI??
MAgnetric resonance Imaging: When we apply magnetic field --> Hydrogen from water molecule starts moving in direction of Field ,rate of spin depends  on strength of magnetic field ...now if you remove magnetic field --> Hydrogen will try to come back to normal ...

In a typical T₁-weighted image, water molecules in a sample are excited with the imposition of a strong magnetic field. This causes many of the protons in water molecules to precess simultaneously, producing signals in MRI. In T₂-weighted images, contrast is produced by measuring the loss of coherence or synchrony between the water protons. When water is in an environment where it can freely tumble, relaxation tends to take longer. In certain clinical situations, this can generate contrast between an area of pathology and the surrounding healthy tissue.
spinning will produce contarst---faster in free flowing water like Ventricle...while slower in gret-white matter.while negligible in bone

Diffusion weighted MRI:
In diffusion-weighted images, instead of a homogeneous magnetic field, the homogeneity is varied linearly by a pulsed field gradient. Another gradient pulse is applied in the same direction but with opposite magnitude to refocus or rephase the spins. The refocusing will not be perfect for protons that have moved during the time interval between the pulses, and the signal measured by the MRI machine is reduced. This reduction in signal due to the application of the pulse gradient can be related to the amount of diffusion that is occurring.
The first successful clinical application of DWI was in imaging the brain following stroke in adults. Areas which were injured during a stroke showed up "darker" on an ADC map compared to healthy tissue. At about the same time as it became evident to researchers that DWI could be used to assess the severity of injury in adult stroke patients, they also noticed that ADC values varied depending on which way the pulse gradient was applied. This orientation-dependent contrast is generated by diffusion anisotropy, meaning that the diffusion in parts of the brain has directionality. This may be useful for determining structures in the brain which could restrict the flow of water in one direction, such as the myelinated axons of nerve cells (which is affected by multiple sclerosis). However, in imaging the brain following a stroke, it may actually prevent the injury from being seen. To compensate for this, it is necessary to apply a mathematical operator, called a tensor, to fully characterize the motion of water in all directions.
Diffusion-weighted images are very useful to diagnose vascular strokes in the brain. It is also used more and more in the staging of non small cell lung cancer, where it is a serious candidate to replace positron emission tomography as the 'gold standard' for this type of disease. Diffusion tensor imaging is being developed for studying the diseases of the white matter of the brain as well as for studies of other body tissues


FLAIR:
Fluid Attenuated Inversion Recovery (FLAIR)^[27] is an inversion-recovery pulse sequence used to null signal from fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid (CSF) so as to bring out the periventricular hyperintense lesions, such as multiple sclerosis (MS) plaques. By carefully choosing the inversion time TI (the time between the inversion and excitation pulses), the signal from any particular tissue can be suppressed

neural foraminal stenosis