VASCULAR 

Acute ischemic stroke: A-41-year-old-male-patient-with-complaints-of-right-upper-and-lower-limb-weakness-for-2-days.[Fig 1] MRI: Areas of diffusion restriction (Images A and B, yellow arrows) with T2 FLAIR hyperintensities (Image C, purple arrows) and no blooming involving left fronto-parietal and insular regions (MCA, MCA-ACA watershed and MCA-PCA watershed areas) – suggestive of Acute non-haemorrhagic infarcts. ASL shows reduced cerebral blood flow in involved areas (Image E, red arrow).

Left Internal Carotid Artery Thrombosis: A-69-year-old-male-came-with-complaints-of-right-upper-limb-and-lower-limb-weakness-for-2-days.[Fig 2] MRI: Multiple foci of diffusion restriction with T2 FLAIR hyperintense signal noted in the subcortical and deep white matters of the left temporal-parietal lobes and periventricular white matter  (Image A, yellow arrows) suggestive of acute non-hemorrhagic infarcts. On TOF IC-EC MRA thrombosis in right vertebral artery and left ICA, with reduced flow signals observed in the left MCA (Images E and F, purple arrow) .ASL shows reduced perfusion in the left cerebral hemisphere (Image G, red arrow).

Carotid stenosis: A-68-year-old-female-came-with-complaints-of-dizziness-since-1-week.[Fig 3] CT EC angiography shows focal narrowing of carotid bulb with eccentric vessel wall calcification causing luminal narrowing (Image A, green arrow).ASL shows reduced perfusion in the right cerebral hemisphere. (Image B , red arrows) 

Arterio-venous malformation: A-49-year-old-male-with-complaints-of-headache-since-one-month.[Fig 4] MRI: Area of multiple serpiginous vessels with a central nidus and multiple flow voids in the right frontal region (Image A, yellow).It is arising from the M1 segment  of the right MCA (Image B & C, blue arrows).ASL shows increased cerebral blood flow within the lesion (Image D, white arrow). 

Diffusion Perfusion Mismatch: A-2-year-old-male-child-with-complaints-of-left-upper-limb-weakness-since-6-hours.[Fig 5] MRI:  Multiple foci of gyral diffusion restriction (Image A & B, green arrows) and corresponding T2 FLAIR hyperintensity (Image C, blue arrow).Relative increased volume of hypoperfusion on ASL involving right frontal lobe (Image D , yellow arrow) in comparison to the segmented volume on ADC depicting ischemic penumbra. 

NEOPLASTIC 

Brain metastases: A-44-year-old-female-patient-with-diagnosed-breast-carcinoma,-now-presenting-with-seizures. [Fig 6] MRI: T1 hypointense lesion in right parietal lobe (Image A, purple arrow), T2 FLAIR isointense lesion with perifocal edema (Image B, yellow arrow). Post-contrast images show avid homogeneous enhancement (Image C, green arrow). Increased cerebral blood flow within the lesion on ASL (Image D, red arrow).

Meningioma: A-45-year-old-female-with-complaints-of-severe-headache-for-3-months. [Fig 7] MRI:  A well-defined T1 hypointense (Image B, green arrow)/T2 isointense (Image A, purple arrow) extra-axial lesion with avid contrast enhancement (Image C, yellow arrow) in the left frontal region with vasogenic edema and midline shift. ASL shows increased cerebral blood flow within the lesion (Image D, red arrow).

Primary CNS lymphoma: A-55-year-old-male-with-behavioral-changes-for-3-weeks.[Fig 8] MRI: An ill-defined, diffusion-restricting (Image A, yellow arrow), T1 hypointense (Image B, green arrow) and T2/FLAIR hypointense lesion (Image C, blue arrow) with  perifocal edema in right frontal lobe. The lesion shows patchy post-contrast enhancement (Image D, purple arrow). There is decreased cerebral blood flow in the lesion on ASL (Image E, red arrow).

Glioblastoma multiforme: A-48-year-old-female-with-complaints-of-seizures-associated-with-headache-and-vomiting.[Fig 9] MRI:  An intra-axial supratentorial, multilobulated lesion in right medial temporal lobe. It is T1 hypointense/T2 hyperintense (Images A and B, yellow arrows) with peri-lesional edema and shows thick peripheral enhancement and central non-enhancing core, suggestive of necrosis (Image C, purple arrow). Multiple intra-lesional foci of blooming are seen on SWAN, suggestive of hemorrhage (Image D, green arrow). ASL shows increased cerebral blood flow within the lesion (Image E, red arrow).

Diffuse glioma:A-45-year-old-female-with-complaints-of-right-sided-headache-for-1-day-and-1-episode-of-focal-seizures-1-week-ago.[Fig 10] MRI: Ill-defined, diffusion hyperintense (Image A, green arrow), T1 hypointense (Image D, blue arrow), T2/FLAIR hyperintense lesion (Image B, yellow arrow) and non-enhancing on post-contrast T1 images (Image E, purple arrow) with perifocal edema in right frontal temporal region with mass effects. ASL shows increased cerebral blood flow in right fronto-parietal lobes (Image C, red arrow).

Focal leptomeningeal mass - meningeal carcinomatosis: A-65-year-old-female,-K/C/O-carcinoma-left-breast,-post-mastectomy-(2006)-and-on-tamoxifen-for-5-years-complaints-of-numbness-in-right-arm-and-on-right-side-of-the-face.[Fig 11] MRI: Multiple non-restricting nodular enhancing leptomeningeal lesions (Image A & B, red arrows) with peripheral vasogenic edema (Image E, maroon arrow) in left central sulcus. Leptomeningeal lesions with peripheral enhancement were noted (Image D & F, purple arrows). ASL shows reduced perfusion in the region of the lesion (Image G, green arrow).

INFECTIVE 

Neurocysticercosis: A-48-year-old-female-with-complaints-of-tingling-sensation-in-the-left-upper-and-lower-limbs. [Fig 12] MRI: A well-defined T2 FLAIR hypointense (Image A, green arrow)/T1 hypointense (Image C, blue arrow) ring-enhancing lesion (Image B & E, yellow arrow) demonstrating ‘cyst-with-dot-sign’ in right high parietal region with T2 FLAIR hyperintense perifocal edema (Image A, purple arrow). ASL shows increased cerebral perfusion in the region of ring-enhancing lesion (Image C, red arrow) and decreased cerebral perfusion in the region of perifocal edema (Image C, white arrow).

Tuberculoma with meningitis: A-43-year-old-male-who-is-HRV-positive,-with-complaints-of-persistent-throbbing-headache-for-6-weeks. [Fig 13] MRI: Few rounded lesions involving bilateral cerebral hemispheres, evidenced by concentric rim diffusion hyperintensity (Image A, green arrows) with low signal intensity on T1 (Image D, purple arrow) and high signal intensity on T2 FLAIR images (Image B, blue arrows) with an additional subtle post-contrast ring enhancement (Image E, white arrow) and pachymeningeal enhancement (Image B, red arrow). ASL shows decreased perfusion in the region of lesion (Image C, yellow arrow).

Cerebral abscess:A-48-year-old-male-found-unconscious-with-3-episodes-of-seizures-on-arrival-to-ER. [Fig 14] MRI:  A well-defined diffusion-restricting lesion (Image A & B, green arrows), T1 hypointense (Image E, yellow arrow), T2 FLAIR hyperintense (Image D, blue arrows) thick-walled collection with peripheral post-contrast enhancement (Image F, white arrow) in right frontal region with fluid-fluid levels, mild perifocal FLAIR hyperintense edema, and subtle hemosiderin staining on SWAN (Image C, purple arrows). ASL shows decreased cerebral blood flow within the lesion (Image G, red arrow).

Cortical encephalitis: A-27-year-old-male-with-complaints-of-seizure-and-altered-sensorium.[Fig 15] MRI: Areas of gyral diffusion restriction (Image A and B, yellow arrows) with FLAIR hyperintensity (Image C, yellow arrows) involving left parieto-temporal region. Sulcal hyperintensities  in right parietal region. Symmetrical diffusion restriction with T2 FLAIR hyperintensity in the bilateral mesial temporal region, suggesting post-ictal changes (Purple arrows). Increased cerebral blood flow in left parieto-temporal and right parietal regions on ASL (Image D, red arrows).

Intracranial caseating tuberculomas with meningitis: A-57-year-old-male-with-complaints-of-intermittent-headache-and-fever-since-3-weeks. [Fig 16] MRI: Few intra-axial ring-enhancing lesions (Image D & F, yellow arrows) in  right frontal lobe with corresponding central diffusion restriction (Image A & B, purple arrows), central T1 hypointensity (Image C, blue arrows) and T2 FLAIR hypointensity (Image E, maroon arrows) with peripheral T2 FLAIR hyperintensity (Image E, maroon arrows), T1 hyperintense rim (Image C, blue arrows) and pachymeningeal enhancement (Image D & F, red arrow). ASL shows increased perfusion in the region of the lesions (Image G, white arrows).

NEURODEGENRATIVE 

Alzheimer’s disease: A-70-year-old-male-patient-with-complaints-of-cognitive-decline.[Fig 17] MRI: T2 FLAIR shows diffuse cortical atrophy with parietal (Image A, green arrows) and temporal predominance (Image B, yellow arrows). ASL shows reduced CBF in the bilateral parietal (Image C, purple arrows) and temporal regions (Image D, red arrows).

Dementia with Lewy bodies: A-76-year-old-male-with-complaints-of-forgetfulness-and-bilateral-upper-limb-tremors. [Fig 18] MRI: Diffuse cerebral atrophy with parietal predominance (Image A). ASL shows reduced CBF in the bilateral parietal lobes and occipital lobes (Image C, red arrows) with focal increase in CBF of the posterior cingulate cortex (‘Cingulate island sign’) (Image B, purple arrow).

MISCELLANEOUS 

Interictal state: A-2-year-old-child-with-seizures-and-transient-left-sided-weakness.[Fig 19] MRI: No foci of diffusion restriction (Image A). Asymmetrically prominent hypointense cortical veins in right fronto-parietal regions on SWAN (Image B, yellow arrow). Reduced CBF in right fronto-parietal regions on ASL (Image C, red arrow).

Hemiplegic migraine: A-36-year-old-female-patient-with-complaints-of-severe-headache-with-aura-and-transient-left-sided-weakness.[Fig 20] MRI: No foci of diffusion restriction or gyral thickening on T2/FLAIR. ASL shows increased CBF in right fronto-parietal regions (Image C, red arrow).

Progressive Supranuclear Palsy: A-67-year-old-male-with-complaints-of-abnormal-eye-movements-postural-instability-and-falls.[Fig 21] MRI:  T2 FLAIR image (Image A) shows reduction in the anteroposterior midline midbrain diameter (yellow arrows) – ‘Mickey-Mouse-sign’. T2 FLAIR midline sagittal image (Image B) shows reduction in midbrain width (blue arrow) with associated reduced midbrain-to-pons width ratio (green arrow) and T2 FLAIR midline sagittal image (Image C) shows flattening of superior aspect of midbrain (purple arrow) - Hummingbird sign. ASL shows a relative decrease in CBF in bilateral frontal lobes (Image D, red arrows).

Localizing focus of seizures: A-54-year-old-male-with-complaints-of-headache-2-episodes-of-seizures-and-altered-sensorium-associated-with-giddiness-and-blackouts-since-1-week.[Fig 22] MRI:  Prominent tortuous cortical veins evidenced by T2 FLAIR hyperintensity in left parietal and occipital regions. ASL shows increased perfusion in left parietal and occipital regions.