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Things You Need To Know About PET Scan

There are questions with regard to PET-Scan. By and large the name of the scan in English is "positron emission tomography”. In nuclear medicine exam often called PET or positron emission tomography. The process of PET scan is pretty much the same as scintigraphy wherein the analyzing the functioning of an organ or a structure of the body is done by using a contrast product injected into the patient. The radiotracer gets activated by coming in contact with the organs and in the presence of an anomaly.


Images of these reactions are captured by a machine and reproduced on a computer screen. The three-dimensional reconstruction makes it possible to visualize the zones of high concentration of the tracer (zones in red). The doctor can identify an abnormality or pathology. As one of the primary advantage, A PET scan allows the obtaining of 3D cuts, which is not the case of scintigraphy. This comes out as a useful method in oncology for detecting or monitoring a tumor.

Why prescribe a tomography?

PET CT scan is mainly prescribed:

  • For the detection of metastases, to know the effectiveness of treatment put in place or to confirm a tumor recurrence when a blood test revealed an increase in tumor markers.
  • In cardiology to study the functioning of the myocardium (for example after a heart attack) or coronary arteries
  • In neurology to confirm the presence of brain damage and degenerative disease such as Alzheimer's or Parkinson's disease.

How does a PET scan work?

In terms of the time duration, the PET scan takes about two hours. Intravenous injection of the radioactive substance is the first step. The patient is kept laid down for one hour in a usual basis. It is the standard time required in order to have the contrast material to enter the body and reach the organs to be examined. The patient is then placed for about twenty minutes in a machine equipped with a ring-shaped opening whilst they are still lying on their back. That's when PET images are created. The results cannot be put out or discussed immediately as it takes some time for study and analysis of the image.

Some of the health conditions determined in PET scan are:

  • The presence and nature of tumor lesions, recurrence of the disease or metastasis of cancer at an early stage;
  • The presence of vascular disorders, post-traumatic changes, foci of epilepsy and Parkinsonism in the brain, as well as causes of dementia;
  • The viability of the myocardium (heart muscle) in ischemic heart disease, congenital heart defects.
The Reason Why MRI Scan Is So Noisy

It is not debatable that MRI scan has been one of the most reliable and best tests for getting diagnosis of multiple ailments and to obtain images of the internal organs of the body. But the question remains why the test procedure or the equipment for that matter is so noisy. So let us figure out.


The Magnetic Resonance imaging machine is basically composed of a powerful magnet, mostly superconductors, with a transmitter and a radio wave receiver, in addition to all the electronics needed to coordinate its operation. It is the reason why the magnet creates a powerful magnetic field even more powerful than that of the earth, the transmitter, in turn, emits radio waves that are directed towards the patient. These waves activate the protons of the different tissues and the receiver picks up the emitted signal with which will create the image.

The MRI machine has four magnets, one main, the largest and most powerful, and the other three smaller ones are the gradients. These smaller ones are inside a large metal coil called the gradient coil. The gradient coil is made of copper electromagnets that create a secondary magnetic field in each of the three directions of space and fulfil a fundamental function since they are responsible for spatially locating the Magnetic Resonance signal and encoding it to create the image that is performed by MRI scan centre in East Delhi.

Why so much acoustic noise? To generate the magnetic field an electric current has to be applied and when it is applied in the presence of a static magnetic field they produce variable magnetic forces that act on the gradient coil (mechanical vibration) and causes it to expand and contract rapidly in a matter of milliseconds producing movements or vibrations generating the noise that is manifested throughout the room, so we can say that the main reason the noise generated by the RM machine present in the MRI test labs in Delhi are the gradient coils.

There are other factors that contribute to generate noise such as the modification of acquisition parameters, acoustic noise tends to improve with the decrease of the thickness of cut, the field of vision (FOV), TR (repetition time) and TE ( echo time) but this may affect the resulting image.

On the other hand, the characteristics of the acoustic noise have a spatial dependence depending on the position and the size of the patient the levels can vary in about 10dB.

Studies conducted including a variety of pulse sequences where several gradients are applied resulted in this type of sequence (3D and GR) being among the strongest with levels ranging from 103 - 113 dB. Other studies also measured the acoustic noise generated by the echo-planar (EPI) and the FSE (fast spin-echo) sequences in 1.5T, noise levels ranging from 114 to 115 dB and at 3T levels in the range of 126 to 131 dB for these noise levels the use of hearing protection is recommended.

General Electric GE developed a technology called Silent Scan a few years ago that allows to reduce acoustic noise to a level similar to that of ambient sound, if we take into account that an RM scanner without this technology generates a noise of approximately 100 dB, depending on several factors, this decrease of almost 30 dB causes greater patient satisfaction and generates a more pleasant silent and comfortable experience.

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