MRI scan

During a MRI scan, pictures of almost all the tissue in the body are taken. The tissue that has the least hydrogen atoms, such as the bones turns out dark. The tissues that have many hydrogen atoms, such as fatty tissue looks much brighter. The timing of the radio wave pulses is constantly changed to gain information about the different types of tissues present. An MRI scan is normally used as an extremely accurate method of disease detection and structural abnormalities throughout the body.

Patient with any metallic materials within the body must notify their physician prior to the MRI scan. This is because, metallic chips, materials, metal implants, surgical clips or foreign materials (artificial joints, metallic bone plates or prosthetic devices, etc) can significantly distort the images obtained by an MRI scanner. Patients with pacemakers, metal chips or clips in and around the eyeballs cannot be scanned by an MRI because of the risk that the magnet may move the metal in these areas. Patients with artificial heart valves, metallic ear implants, bullet fragments and chemotherapy or insulin pumps should not undergo MRI scanning.

MRI scan can cause a small risk to the fetus in the first 12 weeks of pregnancy. Therefore scans are not performed on pregnant women. The MRI machine produces loud thumping and humming noise when the procedure is performed. Therefore ear plugs are usually given to the patients to reduce the noise. MRI scans are a useful aid in the assessment of certain back conditions. MRI is an aid to detail studies of nerve root injuries like lumbar disc herniation and lumbar spinal stenosis. It is also extensively used in spinal disc and lumbar disc diseases and isthmic spondylolisthesis. It is also useful to rule out tumors and spinal infections.

Ultrasound

Ultrasonography is a medical imaging technique that is also called ultrasound scanning or sonography. High frequency sound waves and their echoes and used in this technique for obtaining images from inside the human body. The echoes of sound waves reflected from the human body are recorded and displayed as a real-time visual image. This technique is similar to the echo location used by bats, whales and dolphins. The sonar used by submarines also operates with the same technique. Ultrasound is useful method to examine many of the body's internal organs like heart, liver, gallbladder, spleen, pancreas, kidneys and bladder.

Ultrasound Scanning

1. Sound Waves: A transducer (a small handheld device) emits high-frequency sound waves.
   
2. Echoes: These sound waves bounce off tissues, organs, and other structures inside the body.
   
3. Image Formation: The transducer detects the echoes and sends this information to a computer, which creates images based on the patterns of the echoes.
   

Types of Ultra sound:

1. Abdominal Ultra sound: Evaluates organs in the abdomen, such as the liver, gallbladder, spleen, pancreas, and kidneys.
   
2. Pelvic Ultra sound: Assesses reproductive organs (uterus, ovaries) and bladder.
   
3. Obstetric Ultra sound: Monitors pregnancy and fetal development, to assess the risk of fetal abnormalities such as neural tube defects or Down's syndrome
   
4. Cardiac Ultrasound (Echocardiogram): Evaluates heart structure and function.
   
5. Doppler Ultra sound: Measures blood flow through vessels.
   
6. Musculoskeletal Ultra sound: Examines muscles, tendons, and joints.
   
7. Thyroid Ultra sound: Evaluates the thyroid gland.
   

Preparation:

• Fasting: May be required for certain abdominal ultrasounds.
  
• Full Bladder: Often necessary for pelvic ultrasounds.
  
• Loose Clothing: Wear comfortable, loose-fitting clothes for easy access to the area being examined.
  

Procedure:

1. Preparation: The patient may be asked to lie on a table and expose the area to be examined.
   
2. Application of Gel: A special gel is applied to the skin to help transmit sound waves.
   
3. Transducer Use: The healthcare provider moves the transducer over the area, capturing images.
   
4. Image Review: The images are reviewed in real-time, and the provider may take multiple images from different angles.
   

Benefits:

• Non-Invasive: No needles or incisions.
  
• Safe: Uses sound waves, not radiation.
  
• Real-Time Imaging: Allows dynamic assessment of moving structures.
  
• Widely Available: Accessible in most healthcare settings.
  

Applications:

• Diagnosis: Identifying and evaluating various medical conditions.
  
• Monitoring: Tracking the progress of diseases or conditions.
  
• Guidance: Assisting in procedures such as biopsies or fluid drainage.
  

Common Uses:

• Pregnancy Monitoring: Checking fetal health and development.
  
• Organ Assessment: Evaluating the liver, kidneys, and other organs.
  
• Cardiac Evaluation: Assessing heart function and detecting abnormalities.
  
• Blood Flow Analysis: Checking for blood clots or poor circulation.
  
• Musculoskeletal Issues: Diagnosing tendonitis, bursitis, or tears.
  

Ultrasound examinations are versatile and essential tools in modern medical diagnostics, providing crucial information for the diagnosis and management of many health conditions.

Carotid Doppler ultrasound scanning is a diagnostic method used to assess blood flow through the carotid arteries, which are the primary vessels supplying the neck and head. This non-invasive modality is employed in the evaluation of various conditions, including:
1. Carotid artery stenosis (narrowing) - a common finding associated with increased risk of stroke. Doppler echocardiography image reveals any narrowing of the arteries or turbu￾lence in blood flow.
Echocardiography is a diagnostic tech￾nique used to evaluate structural and functional abnormalities of the heart including:
1. Heart wall: Detecting changes in thickness, texture or motion.
2. Heart chambers: Assessing size, shape, and function.
3. Heart valves: Evaluating valve leaflet movement, regurgitation and stenosis.
4. Large coronary arteries: Identifying narrowing or obstruction.
In addition to detecting cardiovascular lesions, echocardiography is also employed in the diagnosis of:
1. Congenital heart disease: Abnormalities present at birth.
2. Cardiomyopathy: Heart muscle disorders characterized by impaired function.
3. Aneurysms: Ballooning or dilation of the heart or blood vessel walls.
4. Pericarditis: Inflammation of the pericardial sac surrounding the heart.
5. Blood clots in the heart: Emboli that may have originated from other sources and traveled to the heart.

2. Transient ischemic attacks (TIAs), also known as "mini-strokes" or "warning strokes" - a temporary loss of blood flow to the brain.
3. Stroke - a neurovascular event characterized by permanent disruption of blood flow to the brain.
Doppler echocardiography is a valuable diagnostic tool that enables the measurement of blood flow velocity (speed) within the heart. This modality allows cardiologists to:
1. Assess structural abnormalities: Such as mitral valve prolapse, where the mitral valve leaflets protrude into the left ventricle.
2. Evaluate septal defects: Abnormal openings in the septum that separate the right and left sides of the heart.
By analyzing blood flow velocity, Doppler echocardiography can help diagnose and monitor various cardiovascular conditions, including those affecting the heart valves and septum.

Cataract Surgery: An ultrasound probe is inserted into the lens capsule through a small incision in the cornea. The incision is made using a diamond tipped instrument. The ultrasound probe softens the lens by emitting sound waves. It then sucks out the softened lens tissue. Only the front part of the lens capsule is removed.

Doppler ultrasound is a type of echocardiography that utilizes the principles of Doppler shift to measure the velocity of moving structures. This technique involves transmitting high-frequency ultrasonic waves from an emitter and detecting the frequency changes resulting from the interaction with moving targets, such as blood flowing through a blood vessel.
Doppler ultrasonography has become a widely accepted diagnostic modality for detecting various vascular conditions. Specifically, it is commonly employed to:
1. Identify arterial narrowing or stenosis in the neck, often resulting from atherosclerosis (the accumulation of fatty deposits on artery walls).
2. Detect blood clots (thrombi) within veins, as seen in deep vein thrombosis.
In addition to its vascular applications, Doppler ultrasound is also used for:
1. Fetal monitoring: To non-invasively assess fetal heart rate and detect any potential abnormalities.
2. Dialysis and cardiopulmonary bypass procedures: To monitor for air emboli (air bubbles) that may form during these interventions.
3. Blood pressure measurement: As a non-invasive means to estimate blood pressure, particularly in situations where direct measurement is not possible or practical.
The process begins with the emission of pulses of ultrasound at a specific frequency. As these pulses interact with moving objects, such as red blood cells in a vessel, the frequency of the reflected signals (echoes) shifts due to the Doppler effect. A sensor detects these frequency changes and converts them into meaningful data, providing valuable information about the velocity or flow characteristics of the target structure, for example, blood flow through an artery or vein.

Ancillary term used in ultrasound imaging to describe an anechoic region or structure that does not produce any reflective echoes (sonographic signals) when exposed to ultrasound waves. This is typically seen in structures containing clear fluid, such as:
1. Cysts: Fluid-filled cavities that do not reflect ultrasound signals.
In these cases, the lack of echogenicity allows for better visualization and differentiation from surrounding tissues.
"Echogenic" - A descriptive term used in ultrasound imaging to identify structures that produce reflective echoes or signals when exposed to ultrasound waves. In other words, an echogenic structure is one that generates a strong sonographic signal, allowing it to be visualized and characterized on the ultrasound image.

The frequency of ultrasound waves used in medical imaging varies depending on the type of examination and the depth of the tissue being imaged. Here are some general guidelines:

Common Frequencies:

1. General Diagnostic Ultrasound:
   • Frequencies typically range from 2 MHz to 15 MHz.
     
   
   
2. Abdominal Ultrasound:
   • Lower frequencies around 2 MHz to 5 MHz.
     
   • Lower frequencies provide deeper penetration but lower resolution.
     
   
   
3. Pelvic Ultrasound:
   • Frequencies typically in the range of 3 MHz to 7.5 MHz.
     
   
   
4. Obstetric Ultrasound:
   • Frequencies around 2 MHz to 5 MHz for deeper penetration to view the fetus.
     
   
   
5. Cardiac Ultrasound (Echocardiogram):
   • Frequencies typically range from 2.5 MHz to 5 MHz.
     
   
   
6. Vascular Ultrasound:
   • Frequencies around 5 MHz to 10 MHz.
     
   
   
7. Musculoskeletal Ultrasound:
   • Higher frequencies around 7.5 MHz to 15 MHz.
     
   • Higher frequencies provide better resolution for superficial structures.
     
   
   
8. Small Parts (Thyroid, Breast, Scrotal):
   • Frequencies in the range of 7.5 MHz to 15 MHz.
     
   
   

• Penetration vs. Resolution: Lower frequencies penetrate deeper into the body but produce images with lower resolution. Higher frequencies provide higher resolution images but do not penetrate as deeply.
  
• Tissue Characteristics: Different tissues reflect sound waves differently, so the frequency is chosen based on the specific characteristics and location of the tissue being examined.
  

Specific Frequency Ranges:

1. 2-3.5 MHz: Deep structures like the liver, kidneys, and heart.
   
2. 3.5-5 MHz: General abdominal and obstetric imaging.
   
3. 5-7.5 MHz: Breast, thyroid, and vascular imaging.
   
4. 7.5-10 MHz: Musculoskeletal and superficial structures.
   
5. 10-15 MHz: Very superficial structures and detailed imaging of small parts.
   

Normally the term ultrasound refers to frequencies above 20 kHz (the maximum frequency a human can hear), medical ultrasound utilizes frequencies in the range of several MHz to achieve the necessary balance between resolution and penetration for effective imaging of different tissues and organs.

As you can see from the table above, specific band of frequencies are chosen for optimal imaging.

• Resolution: Higher frequencies provide better resolution, allowing for more detailed images of tissues and structures.
  
• Penetration: The choice of frequency is a trade-off between penetration and resolution. Lower frequencies penetrate deeper but have lower resolution, while higher frequencies provide detailed images of superficial structures.
  

Movement of the internal tissues and organs are captured in ultrasound. Ultrasonography enables the physicians to diagnose a variety of disease conditions and also assess the damage caused to the systems. The ultrasound machine transmits high frequency sound pulses into the human body by using probes. These sound waves that travel into the body hit a boundary between the tissues inside the body and reflect the sound waves to the probe. Some waves travel even further and they reach another boundary and then get reflected back. The waves that are reflected are picked up by the probe and relayed back into the ultrasound machine.

The ultrasound machine in turn calculates the distance from the probe to the tissue or organ by using the speed of sound tissue and the time of each echo's return. The machine displays these distances and intensities of the echoes on the screen. Through the echoes that are produced the sonologist can identify how far away an object is, how large it is, its shape and consistency (fluid, solid or mixed). Two dimensional images are formed and reflected on the screen. Different types of ultrasound are used for different disease conditions. Ultrasound is used in a variety of clinical settings including obstetrics and gynecology, cardiology and cancer detection.

Echocardiogram

An echocardiogram is a diagnostic test that gives the doctor an idea of how the heart appears in motion. An echo uses ultrasound waves to pick up echoes from different parts of your heart. An echocardiogram throws light on the size of the heart and the condition of the heart valves. The pumping capacity of the heart is determined with an echocardiogram. Any damage to heart muscles or valves can be diagnosed with an echocardiogram. An echocardiogram is helpful in detecting any structural problems of the heart, its chambers or blood vessels surrounding it. An echocardiogram is used to detect any blood clots within the heart. This diagnostic test is used to check for causes of irregular heartbeats, enlarged heart or heart murmurs. The functioning of the heart after an attack can be checked with an echocardiogram.

Trans thoracic echocardiogram is the standard cardiogram where the doctor monitors sound wave echoes that bounce off the heart and other internal structures.

Doppler echocardiogram is based on Doppler signals that change pitch when they bounce off the heart and blood vessels. This feature is often part of other cardiogram procedures.

Stress echocardiogram is taken when a patient is undergoing a treadmill stress test.

Trans esophageal echocardiogram involves passing a probe through the throat into the chest wall. The transducer then shows clear images of the heart. This type of echocardiogram can be uncomfortable and is often performed under sedative. Trans esophageal echocardiogram is also used during surgery to monitor the heart function. Abnormal blood flow between the heart's chambers can be detected.