Difference Between VQ Scan and CTA

Numerous scanning tools are available in the medical industry with technical evolution. VQ scan and CTA are diagnostic tools used extensively in nuclear medicine to scan organs.

Ventilation-perfusion scan (VQ) measure and identify blood circulation in the lungs. Computed Tomography Angiography (CTA) utilizes an X-ray machine for a high-quality image.

VQ Scan vs CTA

The main difference between a VQ scan and CTA is that a VQ scan is a medical technique that uses a tracer (a radioactive substance) to diagnose the body organs and majorly scan the lungs. It is effectively used by the radiology department. On the contrary, Computer Tomography Angiography (CTA) is a diagnostic procedure that detects if there is any blood clot in the heart and lungs. It evaluates the pulmonary embolism.

VQ Scan vs CTA

VQ scan is called Ventilation-perfusion scan because this diagnostic test is a two-step procedure used in scanning the lungs. The ventilation scan determines the flow of air, while the perfusion scan measures the blood flow of the lungs.

The medical test technique is used to diagnose if there is any blood clot in the lungs.

Computed Tomography Angiography, also called CT angiography or CTA, is commonly used to diagnose pulmonary embolism and present high-quality images by using an X-Ray machine.

This test is utilized in such a way that enables it to scan blood clots in the lungs and pulmonary arteries. It is considered the first imaging test to detect the possibility of acute pulmonary embolism.

Comparison Table Between VQ Scan and CTA

Parameters of ComparisonVQ ScanCTA
Stands forVQ scan stands for Ventilation-perfusion scan.CTA stands for Computed Tomography Angiography.
How it worksIt diagnoses and measures the airflow and blood flow by using the ventilation and perfusion scan tests respectively.It diagnose pulmonary embolism and produce images of tissues and vessels by combining with a CT scan.
Image qualityVQ scan does not provide good quality images of the diagnosed organ.CTA provides high-quality images as compared to the VQ scan.
Radiation ExposureThe radiation exposure in VQ scan is comparatively less.CTA includes a relatively higher risk of radiation exposure than VQ scan.
AccuracyCompared to CTA, it has lesser accuracy to detect and diagnose the lungs or pulmonary embolism.It has significantly high accuracy.

What is VQ Scan?

A Ventilation-perfusion scan is a diagnostic test of the lungs that is proceeded in two major steps or scans. One measures the airflow, and the other measures the blood flow in the lungs.

The scanning includes a radioactive substance with low risk and provides images of the blood clot.

A Blood clot in the lungs area is known as a pulmonary embolus, and symptoms of this medical condition include breathing problems, rapid heart rate, and chest pain.

The VQ scan takes nearly 40 minutes, and low-risk is associated because the amount of radiation is relatively less.

To measure the airflow, a small amount of radioactive tracer substance is provided to inhale through a nebulizer or mouthpiece. The person lies down, and images of the lungs are captured.

To diagnose the blood flow, another radiopharmaceutical substance is injected, and the images will be taken.

What is CTA?

Computed Tomography Angiography or CTA is a diagnostic tool primarily used to diagnose blood clots, blood vessels, pulmonary embolism-related diseases.

Doctors use X-ray machines and CT scans for the high-quality image of the tissues and blood vessels. There could be numerous reasons for which the doctor recommends this test.

It is used to diagnose and identify abnormal blood vessels that may get damaged due to some injury or formed inside the brain. It also located tumors.

CTA tests are used by healthcare and doctors for cancer treatment and kidney transplants.

It is suggested that this test must be done after checking the medical condition and eligibility because it may cause some side effects, including damaging the kidney if the person is diabetic or have some kidney disease.

Main Differences Between VQ Scan and CTA

  1. VQ scan and CTA are the diagnostic tools used by the radiology department and medical center. VQ scan is comparatively an older medical technique which is a two-step process and stands for Ventilation-perfusion scan. On the contrary, the term CTA stands for Computed Tomography Angiography.
  2. VQ scan and CTA diagnose and detect the PE or pulmonary embolism but vary from each other in one or another way. VQ scan diagnoses and measure the airflow and blood flow by using the ventilation and perfusion scan tests, respectively. CTA, on the other side, diagnoses body organs and produces images of tissues and blood vessels by combining them with a CT scan.
  3. For every diagnostic tool, image quality plays a significant role in highlighting the major issues. The image quality of the VQ scan is not that good as compared to the CTA, as the CTA produces relatively high-quality images.
  4. The diagnosing or scanning test are propagated by using some radioactive or radiopharmaceutical material that works as a tracer. The radiopharmaceutical used surely has some radiation exposure. The radiation exposure of VQ scan is relatively less than CTA.
  5. VQ scan and CTA have an accuracy level that provides relevant information to the doctors regarding the affective organ. If the accuracy is concerned, then for the pulmonary embolism, the images or test report of CTA is significantly more accurate than the VQ scan.


VQ scan and CTA are the diagnostic tools used in medical science to detect pulmonary embolism. Both of these tests method have their significance and usage.

VQ scan is comparatively more sensitive with less risk of radiation exposure, while CTA is commonly used nowadays and provides better-diagnosed images with greater accuracy.

The doctor can recommend any of the tests after examining the medical condition.


  1. https://jnm.snmjournals.org/content/49/1/5.short
  2. https://link.springer.com/article/10.1007/s12149-013-0753-1

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