Introduction

Definition of thrombosis

Thrombosis occurs when a blood clot forms in a blood vessel, blocking the blood flow. This can cause health problems like deep vein thrombosis (DVT) or pulmonary embolism (PE). This might happen due to a damage to blood vessel walls, odd blood flow, and too much clotting, all known as Virchow’s triad.¹

Importance of early and accurate diagnosis

Early detection of thrombosis is key, as it provides the use of medicines to thin the blood sooner. This can disolve clots, which prevents critical health issues like pulmonary embolism (PE). Any delay or neglect in this case could engender sudden collapse and death.²

Overview of imaging techniques used

To detect thrombosis, doctors use tools like Doppler Ultrasound, CT Venography and MRI/MR Venography. Doppler Ultrasound is not invasive, but CT and MR Venography give very clear images of blood vessels. Each tool has its own advantages and disadvantages.^3,4

Doppler ultrasound

Doppler ultrasound is a non-invasive technique that checks blood flow in vessels using the Doppler effect. It uses the Doppler effect to help reveal blood clots in deep veins or narrow arteries.

Principle: The doppler effect

The Doppler effect is about the change in sound or light waves when seen by someone moving compared to the source of the wave. In medical check-ups, when sound waves from a tool hit moving red blood cells, the sound that bounces back changes in step with the speed and path of the blood. This change in sound is then checked and used to find out how fast and where the blood is moving in the body.

Mechanism: types of doppler ultrasound

• Color Doppler imaging:  It uses red and blue to show which way blood flows—red when it moves toward the device and blue when it moves away. It creates a color map of blood moving in tubes, helping spot issues like uneven flow or clogs
• Spectral Doppler imaging: It illustrates blood flow as a chart. The up-down line shows how fast and in which way the blood moves and the left-right line shows time. It helps look closely at how blood moves, checking for things like pulse, crucial for checking blood vessel health
• Power Doppler imaging: It does not show the way blood moves as color Doppler does. Hence, it is better at finding blood flow, even in small or deep blood ways. It helps a lot when examining t parts with slow flow or when color Doppler is not clear

Advantages

Doppler ultrasound offers several advantages in the diagnosis and management of vascular conditions:

• Non-invasive and safe- It does not use harmful rays, which makes it a safe choice for people, even if they need to check it several times
• Real time blood flow assessment- This method produces images of blood flow through the blood vessels. This means we can immediately check for issues like narrow vessels, blockages, and bulging arteries
• Cheap and accessible- When you compare it to other scans such as CT or MRI, Doppler ultrasound costs less, and it is available. This helps in prompt checking and establishing treatment approaches

Limitations

• Lower chance of finding issues in patients without symptoms- In people who do not show signs but are at high risk, for instance, those with a surgical history, this type of body scan does not work well in spotting deep vein issues near the body's core
• The trouble with the scan in certain groups -  It can be weak in people who are overweight, have swelling, are sore, just had hip or knee surgery,  are wearing casts, or cannot move well
• Hard to spot calf vein clots- Ultrasound tests are not as good at finding clots in the calf veins as they are in the bigger veins in the thigh. This issue might cause some lower leg DVT cases to be skipped
• Chances of False-Positive- Outside things, like pressure on a vein from a mass near the pelvis or other nearby issues, can make ultrasound tests generate wrong positive results.^5,6

Computed tomography (CT) angiography

CT Angiography is a non-invasive way to reveal the inside of blood vessels and tissues. It helps discover what's wrong with the body’s blood flow.

Principle

CT Angiography uses usual CT scans and a special dye to produce clear images of blood vessels. The dye makes the blood vessels more visible by blocking some X-rays. This allows doctors to distinguish between blood vessels and nearby tissues. With this method, doctors can check if the vessels are open, detect blockages, bulges, and other issues in the vessels.

Mechanism

• Contrast administration: A contrast agent, often with iodine, is put into the blood through a vein. This agent takes in X-rays, generating the blood paths clear in pictures
• CT imaging: Fast, sharp CT scans are done right after the contrast is injected. The X-ray beams move around the person, taking detailed images of the body
• Image reconstruction: Smart computer methods build the taken pictures into clear, 3D images of the blood paths. This lets us see the blood move well and find anything odd.⁷

Advantages 

• High temporal resolution – Dual-source CT cuts down on blurs, making heart images clear
• Dual-energy imaging – Captures images at two power levels, helping spot tissues better and cutting down on errors
• Non-invasive – Skips the need for placing tubes in arteries, lessening the chances of bleeding or infection
• Rapid processing – Enables fast imaging, quick checks and treatment necessary in emergencies
• Comprehensive assessment – Offers explicit blood vessel imaging for the correct spotting and care plans
• Prognostic value – Research shows that heart scans promote lower chances of dying from heart problems or attacks⁸

Limitations 

1. Radiation exposure – Ionizing rays can increase cancer risk, so we must be careful, more so in young patients
2. Contrast-induced nephropathy – Iodine dye may hurt the kidneys thus we need a kidney check before scans
3. Calcification artifacts – Severe artery calcification can distort lumen assessment, affecting accuracy
4. Metallic artifacts – Implants like stents can mess up the image quality, making the test difficult
5. Limited access – Requires advanced equipment and trained people, limiting its use.⁹

Magnetic resonance imaging (MRI) and MR venography

MRI is a safe way to see inside the body that uses big magnets and radio waves to make clear pictures of the body's internal structures. Unlike methods that use ionising radiation, MRI provides high quality images of soft tissues, which helps a lot in diagnosing health issues.

Principles of MRI

MRI works by using nuclear magnetic power. When put in a strong magnet field, hydrogen protons in the body line up with that field. When radio waves hit, they break this line up, and as the protons go back to how they were, they give off signals. These signs are picked up and turned into pictures by a computer, showing the internal organs of the body.¹⁰

Magnetic resonance venography (MRV)

​​MRV is a type of MRI that focuses on veins. It uses magnetic resonance technology, usually with intravenous contrast dye, to visualise the structures of the vein. This dye makes the blood flow stand out more, helping to spot issues like deep vein clots, weak veins, or vein changes.¹¹

Advantages

• Non-ionising radiation: MRI does not use rays that can harm the body, cutting down the risk from ray harm
• Superior soft tissue contrast: MRI provides excellent contrast between different soft tissues, helping to find and know more about different health problems
• Multiplanar imaging capability: MRI can obtain images from many sides without moving the person, giving a full view of the body's layout

Limitations

• Contraindications: Those with certain body implants like heart pacers or ear implants can't have MRI considering the strong magnets may harm them
• Longer scan times: MRI scans take a lot of time, making it hard for people who struggle to stay still
• Sensitivity to motion: If the person moves, the picture quality drops, often needing the scan to be done again¹⁰

Summary

• Thrombosis definition: It appears when a blood clot forms inside blood vessels and may lead to major health risks such as DVT or PE
• Early diagnosis importance: Early detection means we can adequately treat it on time, preventing serious issues like collapse or death
• Imaging techniques: Including Doppler Ultrasound, CT Venography, MRI/MR Venography, and Pulmonary Angiography

Doppler ultrasound

• Utilises the Doppler Effect to evaluate blood flow
• Types: Color Doppler, Spectral Doppler, Power Doppler
• Advantages: Non-invasive, real-time imaging, inexpensive
• Limitations: Not so good in patients with no symptoms, obese, or for lower leg vein clots

CT angiography (CTA)

• Uses contrast dye and X-rays for clear vascular imaging
• Advantages: High accuracy, rapid processing, non-invasive
• Limitations: Radiation exposure, kidney risk from dye, issues with metal implants

MRI & MR venography

• Employes magnetic fields and radio waves to visualise veins
• Advantages: No radiation, clear view of soft-tissue, images from multiple angles
• Limitations: Takes a long time, movement sensitivity, not for those with implants