Atlas of BRAIN MRI

Brain magnetic resonance imaging (MRI) is a common medical imaging method that allows clinicians to examine the brain’s anatomy⁽¹⁾. It uses a magnetic field and radio waves to produce detailed images of the brain and the brainstem to detect various conditions⁽²⁾. These include tumors, inflammatory ailments, and developmental and structural abnormalities.

Given the different pathological conditions that MRI can help detect, it is vital to understand the brain’s anatomy as seen on MRI.

How Does Brain MRI Work?

Unlike X-rays or computed tomography (CT) scans, MRI does not use radiation. However, the procedure may last for 30 minutes to 2 hours⁽³⁾.

Moreover, magnetic resonance imaging is often the most sensitive imaging technique in assessing the structure of the brain and spinal cord⁽⁴⁾. MRI excites the tissue hydrogen protons, emitting electromagnetic signals back to the MRI machine. This MRI machine detects the signals’ intensity and translates the result into a gray-scale image.

Contrast agents, like gadolinium, may be given through an IV to increase the visibility of the body’s internal structures.

The most common MRI sequences used include T1-weighted (T1w) and T2-weighted (T2w) scans⁽⁵⁾. T1w sequences display those structures mainly made with fat. Thus, they reveal gray matter as gray, white matter as white, bones as black, and cerebrospinal fluid as black. 

Meanwhile, T2w sequences highlight structures containing more water. These sequences display the gray matter as gray, white matter as darker gray, bones as black, and cerebrospinal fluid as white. 

The orientation is another vital element of the scan. Three MRI orientations include axial (from top to bottom), coronal (from front to back), and sagittal (side to side) views⁽⁶⁾.

Brain Anatomy

Part of the central nervous system, the brain is an essential organ that regulates memories, thoughts, emotions, motor skills, and all other processes involved in the body⁽⁷⁾.

Cerebrum

The cerebrum or front of the brain consists of the right and left hemispheres⁽⁸⁾. Its main functions include the initiation and coordination of movement, reasoning, problem-solving, emotions, learning, touch, vision, and hearing.

Brainstem

The brainstem is the middle part of the brain, including the medulla, pons, and midbrain⁽⁹⁾. Its main functions include relaying sensory information, like pain, eye and mouth movement, involuntary muscle movements, respirations, hunger, consciousness, and cardiac function.

Medulla

The medulla oblongata is the lowest part of the brainstem and is the most crucial part of the brain⁽¹⁰⁾. It contains important control centers for the heart and the lungs. 

Pons

Pons is a deep part of the brain located in the brainstem⁽¹¹⁾. It possesses many of the control areas for the movement of the eyes and face. 

Midbrain

Midbrain refers to the shortest segment of the brainstem⁽¹²⁾. However, it has several structures necessary to maintain different body functions, such as processing auditory and visual information and controlling movements of the eyes and face.

Cerebellum

The cerebellum is the back of the brain located at the back of the head⁽¹³⁾. Its main functions include coordinating voluntary muscle movements and maintaining posture and balance.

Brain Lobes

Some pathological conditions may be observed from specific brain lobes⁽¹⁴⁾. These brain lobes consist of the frontal lobe, parietal lobe, occipital lobe, temporal lobe, limbic lobe, and insular lobe.

Frontal Lobe

The frontal lobe refers to the brain’s largest section located at the front of the head⁽¹⁵⁾. Moreover, the frontal lobe is responsible for personality characteristics, movement, and recognition of smell.

Parietal Lobe

The parietal lobe is the middle part of the brain that helps individuals recognize objects and comprehend spatial relations⁽¹⁶⁾. This lobe is responsible for pain interpretation and touch.

Occipital Lobe

The back part of the brain — the occipital lobe — is involved with vision⁽¹⁷⁾. 

Temporal Lobe

The temporal lobe refers to the brain’s sides responsible for short-term memory, musical rhythm, and speech⁽¹⁸⁾.

Limbic Lobe

Lying deep in the parietal and frontal lobes, the limbic lobe is a functional unit usually called the limbic system⁽¹⁹⁾. It helps influence bodily functions, like memory, learning, and behavior⁽²⁰⁾.

Insular Lobe

Lying lateral to the extreme capsule of basal ganglia, the insular lobe is a small part of the cerebral cortex found deep within the meeting point of the temporal, parietal, and frontal lobes⁽²¹⁾. The insular lobe plays a role in autonomic control,  pain processing, and taste perception⁽²²⁾.

Different Conditions That Brain MRI Can Detect 

 Brain MRI may help detect specific abnormalities or conditions in the brain⁽²³⁾. These include: 

• Tumors
• Aneurysms
• Congenital abnormalities
• Hemorrhage, or bleeding into the brain or spinal cord
• Hydrocephalus or fluid in the brain
• Degenerative diseases, multiple sclerosis, encephalomyelitis (inflammation of the brain or spinal cord), and hypoxic encephalopathy (dysfunction of the brain caused by lack of oxygen)

Thus, understanding the brain anatomy and how MRI works can help one learn MRI’s essential role in detecting brain-related conditions.