Sinusitis is an inflammation of the membrane of the sinuses in the nose. These are called the paranasal sinuses and are a part of the upper airways. They are connected to the nasal cavity. Sinusitis can be caused by infection, autoimmune problems or an allergy. Normally, it would be resolved in 10 days. [1]
0.5% of the upper respiratory tract infections result in sinusitis. It is common in adults, but not so common in children, because they don’t have fully developed sinuses. [3]
The paranasal sinuses are the frontal sinuses, the sphenoid sinus, the ethmoid sinus and the maxillary sinus. These cavities are called after the bones that lay around them. They are found all throughout the head. (Picture 1) [1] The sinuses are lined with a mucous membrane which can become infected. Their function is to humidify, filter and warm the air going into the airways. It also senses what is in the air ‘ an unspecific defence mechanism. [2]
Picture 1 The nose and sinuses around the nose [4]
People feel weak, ill and have fever if they have sinusitis. They can also have extreme pain in their face. [5] The physical examination includes inspection of ear, nose and throat. Also checking if the mucous membrane that is visible (nose) is red/swollen ‘ if so than sinusitis is usually present. Palpation of face for pain and swelling. Pain over bridge of the nose ‘ ethmoid sinus, pain behind eyes/headache ‘ sphenoidal sinus, pain above eye ‘ frontal sinus and pain in cheeks ‘ maxillary sinus. [4] Diagnostic tests are furthermore nasal endoscopy, imaging studies (mostly CT or MRI scan), nasal and sinus cultures (when treatment doesn’t work) or allergy testing (when this is the cause). [6]
Treatment involves steroids, painkillers, nasal sprays, saline solutions and/or antibiotics. [5]
Classification of sinusitis depends on two things: duration of the symptoms and changes in the membrane. [6]
– Acute sinusitis
Treatment gives relieve of the symptoms and makes them go away. The membrane will go back to the normal state.
– Chronic sinusitis
Not treated or falsely treated acute sinusitis.
Physics of Conventional Radiography
Electrons are send from the ‘ pool to the + pool (the target) through the x-ray tube. When the electrons hit the target, x-rays are created. X-rays are photons packed into small energy packages. [7] The photon is made in one of two ways:
– Via bremsstrahlung
This means that the electron is send into an atom and the pathway that the electron takes will change. With this change a photon is released. This gives a continuous energy spectrum.
– Via characteristic radiation
This means that the electron goes from the outer layers of the atom to an inner layer with transmission of a photon. This will give specific energies.
X-rays are weaker (attenuated) by absorption and scattering. How weak the x-ray is depending on the material thickness, the material composition and the x-ray energy. If the photon energy goes up then the attenuation goes down (so stronger signal at the detector). It is furthermore, tissue dependent. The attenuation of air is zero. The attenuation of fat is lower than that of muscle and the attenuation of muscle is lower than that of bone. This will mean that when the x-rays are send through the body, they are received with different strengths at the detector (Picture 2). This gives different contrasts. Air will be black, fat and muscle grey and bone white. So, the contrast in soft tissues is poor, but between air, soft tissue and bone the contrast is good. [7]
Picture 2 X-ray system [8]
An x-ray makes a 2D image. Contrast agent will make specific tissues more visible. The picture is made fast, so the patient doesn’t have to lay super still for long in the machine. (Picture 3+Picture 4) There are a few negative points. Because it is only a 2D image, it can’t be known if the object is at front or at the back of the patient. Furthermore, multiple parts are projected over each other, this will mean that there should be multiple pictures taken too reduce errors. [7]
Physics of Computed Tomography (CT)
CT is a scan of a 3D volume, which is split into volume elements. With this a slice of the patient’s body is taken, for example a slice of the head. This slice has depth in it and a good soft tissue contrast. (Picture 6+Picture 7)
Computed tomography uses the same principle as conventional radiography. So, it also uses an x-ray tube and the detector picks up the strength of the photons that are made by the electrons changing direction or changing layer in the atom.
The detector has multiple detector elements. The tube and the detector change position around the patient, in a circle form. The detector then gets the strength of the photons at different positions.
The image is reconstructed by back-projection. Back-projection is the attenuation coefficient calculated for each image voxel. So, the strength of the photons is calculated at each location. This value is called the voxel grey value. The voxel grey values of each view put together gives a shade of white/grey/black. If you do this with a lot of views and there is a filter over it than a picture is made. (Picture 3) The attenuation coefficient depends on x-ray energy. This will give a CT number. This number is specific for a structure, so the soft tissues are also different per structure (good contrast between soft tissue structures). [7]
Picture 5 Back-projection [10]
The negative point is that there are 4000 CT-numbers and only 200 visible grey values. That’s why there are subranges within the range of CT-numbers. Each structure in the body has its own window in which the 200 grey values are incorporated. With different windows different structures can be made clear within the same slice of the body. [7]
Because most detectors have multiple elements, there are multiple slices made at the same time. The more elements, the more slices.
Two tubes and two detectors can be used. This will give a lesser time frame where the patient must be lying super still in the machine. [7]
Comparison
Table 1 Clinical Epidemiological Criteria
Conventional Radiography Computed Tomography
Sensitivity 48-67% [12] 95% [13]
Specificity 75% [12] 97% [13]
Positive predictive value 60-70% [14] 100% [14]
Negative predictive value 33-40% [14] 100% [14]
Table 2 Other Criteria
Conventional Radiography Computed Tomography
Cost (‘) 66,- [15] 190,- [15]
Time (minutes) 1 minute [16] 15 minutes [18]
Radiation (mSievert) 0.09 [15] 9 [15]
Risks The radiation level is too low to cause real damage for an adult, but for an developing baby (so also unborn babies) it could be harmful.
If a contrast agent is used than there could be a reaction to this, which could cause hives or itching. [16] [17] The radiation level is higher than that of conventional radiography, but still not high enough to get cancer (after a single scan). For children the risk is higher. Also for unborn and developing babies the radiation can be harmful. [18]
Discomfort to the patient None [16] None [18]
The difference of computed tomography with conventional radiography is that with CT there is no over-projection, there is better tissue contrast and better visualisation of mediastinum, interstitium and vessels. Furthermore, there is a possibility for reconstructions with CT. [19]
Background radiation is normally up to 10 mSievert, so the radiation that comes from taking a conventional radiography is relatively low. [15]
If the patient is not able to lay still and/or when there are more body parts that must be looked at (scan/picture taken off) in the same session, the duration of the procedure can increase. [16]
Computed tomography is most used to diagnose sinusitis. But this procedure is not available everywhere in the world so conventional radiography is still used in these parts of the world, especially in developing countries. [20]’