Brain Imaging Techniques

Cerebral Angiography

• Utilized in the diagnosis of vascular pathologies like atherosclerotic disease, aneurysms, vasculitis, and arteriovenous malformation
• An invasive procedure involving arterial access via the common femoral artery
• A radiopaque contrast agent is injected
• Major cerebral arteries are outlined using X-ray images

Computed Tomography (CT)

• CT scans are advantageous for uncooperative patients
• Useful in identifying fresh hemorrhages and bone fractures
• CT scans involve exposure to ionizing radiation, making them unsuitable for pregnant women and children
• CT scans provide limited distinction between gray and white matter
• CT scans have poor localization of ischemic infarct

Magnetic Resonance Imaging (MRI)

• MRI provides better anatomic detail of normal and abnormal structures compared to CT scans
• Allows viewing of a variety of abnormalities
• Enables differentiation between gray and white matter and tissue and bone
• MRI does not involve exposure to ionizing radiation

WADA Test

• Used to test for cerebral dominance
• Sodium amytal infusion is integrated with angiography
• Induces functional ablation of the brain
• Assumes interruption of language functions after drug infusion
• An integral part of surgical management of epilepsy and tissue removal
• Signs of drug anesthetization include contralateral hemiplegia with interrupted language if dominant for language
• Transient speech arrest with confusion, and no aphasia if the non-dominant hemisphere is affected

Auditory System

• Complete Auditory Pathway: Cochlea -> Cochlear nuclei -> superior Olivary complex -> lateral lemniscus -> inferior colliculus -> medial geniculate nucleus -> primary auditory cortex -> Wernicke's area
• C -> CN -> SOC -> LL -> IC -> MGN -> PAC -> WA
• The Superior Olivary Complex (SOC) processes sound localization cues and sends the information to the Inferior Colliculus (IC)
• The Medial Geniculate Nucleus (MGN) relays the signal to the Primary Auditory Cortex (PAC)
• The Primary Auditory Cortex (PAC) handles final sound processing and interpretation
• Wernicke's Area (WA) aids in speech comprehension

Visual System - Eye

• The retina, a tissue layer at the back of the eye, contains photoreceptor cells called rods and cones, converting light into electrical signals for brain transmission
• Rods are responsible for vision in dim light (night vision)
• Cones are responsible for color vision and sharp detail in bright light

Optic Nerve

• Contains nerve fibers transmitting electrical signals from the retina to the brain
• Information from the left visual field of both eyes is processed in the right hemisphere of the brain
• Information from the right visual field is processed in the left hemisphere

Optic Chiasm

• The point where the optic nerves from both eyes meet and partially cross
• Nasal fibers of the optic nerves (from the inner half of each retina) cross to the opposite side
• Temporal fibers (from the outer half of each retina) remain on the same side
• Visual information continues as the optic tract after passing through the optic chiasm, each tract carrying information from the opposite visual field of both eyes
• The optic tract travels to the Lateral Geniculate Nucleus (LGN) of the thalamus

Lateral Geniculate Nucleus (LGN)

• Acts as a relay station for visual information within the thalamus
• Processes and sorts visual signals before transmitting them to the visual cortex

Optic Radiations

• Visual information travels via optic radiations, which are nerve fibers projecting from the LGN to the primary visual cortex in the occipital lobe

Primary Visual Cortex (PVC)

• The area where the brain begins to process and interpret visual information
• Responsible for detecting edges, colors, and contrasts
• Processes raw form information like outlines, shapes, and colors, and higher-level processing occurs in other areas of the brain

Visual Association Areas

• Visual information is sent to higher-level visual association areas in the occipital, temporal, and parietal lobes for complex processing
• Ventral pathway ("what" pathway): processes object recognition and identification; travels from PVC to the inferotemporal cortex in the temporal lobe
• Dorsal pathway ("where" pathway): processes spatial awareness, motion, and object location; travels from PVC to the parietal lobe

Visual System and Communication

• Language can activate the visual system to create mental imagery
• Brains create mental images to aid understanding and memory when reading or hearing language
• Vision and language are critical for effective communication
• Visual cues and language are often used together to communicate thoughts, feelings, and ideas

Attention and Perception

• Language can direct attention to specific visual stimuli
• Language influences the perception of visual stimuli
• How an object is described linguistically can affect how it is perceived

Pathology of the Central Nervous System - Cardiovascular Accident (Stroke)

• A medical condition where blood flow to the brain is blocked, or a blood vessel bursts inside or on the surface of the brain
• Two types: ischemic or hemorrhagic
• Can result in loss of sensorimotor, speech, and language functions depending on the lesion location

Neoplasm

• It is an abnormal growth of cells in the brain that can be benign or malignant
• Involves invasion of normal structure by uncontrolled cell growth
• Symptoms, depending on the lesion site, may include headaches, seizures, nausea, vision changes, and cognitive difficulties

Demyelination (Multiple Sclerosis - MS)

• The protective covering of nerve fibers is damaged or destroyed by the immune system attacking the myelin sheath or when Milan is impaired by defect, toxins, or other conditions
• As myelin is stripped away, nerve fibers become exposed, slowing or blocking electrical impulse conduction
• Symptoms can be muscle weakness, loss of sensation, balance problems in coordination, and speech and swallowing issues in late stages
• Key symptom: numbness, tingling, or pins and needles sensation

Degeneration (ALS)

• Involves the generation of motor neurons in the brain and spinal cord
• Symptoms include muscle twitches in the arm, leg, shoulder, or tongue, tight and stiff muscles, muscle weakness affecting an arm, a leg, neck, or diaphragm, slurred and nasal speech, difficulty chewing or swallowing, and difficulty breathing

Degeneration (Alzheimer’s)

• A neurodegenerative condition with a slow onset and progressive impairment of behavioral and cognitive functions
• These functions include memory, comprehension, language, attention, reasoning, and judgment

Motor Disorders (Parkinson’s)

• A degenerative disease affecting nuclei in the midbrain and brainstem, caused by the orientation of dopamine-producing neurons in the basal ganglia
• Symptoms include resting tremor, muscle rigidity (unusual stiffness and difficulty moving), slowness and difficulty initiating movement, and impaired balance

Motor Disorders (Cerebral Palsy)

• A neurological disorder affecting movement, muscle tone, and sensory motor skills caused by lack of oxygen during, before, or after birth
• Symptoms: motor symptoms, posture issues, and speech and swallowing difficulties
• Can result in intellectual disabilities, seizures, and vision or hearing problems

Bacterial and Viral Infections

• Viral or bacterial infection inflammatory infection of CNS membrane (e.g., meningitis)
• Symptoms include headache, fever, stiff neck, and long-term cognitive issues

Epilepsy

• Involves seizures, which are uncontrolled bursts of electrical activity that change sensations, behaviors, awareness, and muscle movements
• Can cause sensory motor and cognitive impairments

Traumatic Brain Injury

• Caused by a forceful bump, blow, or jolt to the head or when an object penetrates the skull and enters the brain
• Symptoms depend on the legion site along with cognitive impairment, speech and language, difficulty, and swallowing issues

Somatosensory System

• It involves the bodily experience of eternal and internal sensation (including pain, temperature, touch, and proprioception)
• Transmits sensory information from the body to the brain, enabling the detection of sensations like touch, pain, temperature, and proprioception (awareness of body position)
• Begins with specialized receptors in the skin, muscles, joints, and blood vessels that convert sensation to neural signals and transmit them through the spinal cord to the sensory cortex in the parietal lobe

Types of Sensation

• Mechanoreception (touch, pressure, vibration, proprioception)
• Thermoreception (cold and heat)
• Nociception (Pain)
• Dorsal Column-Medial Lemniscal Pathway (DCML): a sensory pathway that carries information related to fine touch, proprioception (body position sense), and vibration from the body to the brain
• Spinothalamic Tract: transmits information about pain, temperature, and crude touch from the body to the brain

Trigeminal Nerve (Cranial Nerve V)

• The main sensory nerve of the face, responsible for conveying sensations from the skin, mucous membranes, and sinuses of the face to the brain
• Ophthalmic (V1): Sensory information from the forehead, scalp, and upper eyelid
• Maxillary (V2): Sensory information from the middle part of the face, including the cheek, upper lip, and upper teeth
• Mandibular (V3): Sensory information from the lower part of the face, including the chin, lower lip, and lower teeth