Description of computed tomography scans


CT of the central nervous system (CNS)
– makes it possible to assess the nervous tissue, with differentiation of the grey and white matter, the spaces containing cerebrospinal fluid, the ventricular system, and the system of arachnoid cysts. The scan is done without preparing the patient in emergency conditions such as: injury, differentiation of ischaemic and haemorrhage strokes, as well as in diagnostics of subarachnoid haemorrhages (SAH). Besides the abovementioned conditions, the patient should always be on an empty stomach in case it is necessary to administer an intravenous contrast medium. Apart from a very few exceptions, the contrast medium is administered if there is a suspicion of growth processes and/or metastasis, inflammations within the cerebrum, meninges and bones, and if regressive changes or other CNS disorders are suspected.


CT of the pituitary gland
– the scan is performed only in persons with contraindications for the magnetic resonance imaging (MRI) examination, having a better diagnostic value in patients who are suspected of having proliferative lesions of the pituitary gland, most frequently adenomas. Referring the patient to this scan, one should remember that because of the use of thin-section images, it is intended only for the assessment of the pituitary gland, sella turcica, cavernous sinuses and arachnoid cysts, both perisellar and suprasellar.


CT of the petrous pyramid– performed with the spiral and multi-slice technique - a method of choice in CT scans of the petrous pyramid. The protocol of the scan should include slices below 1 mm (submillimetre), available only in multi-slice scanners. The older type of tomograph scanners, in which these options are not available, do not enable staff to obtain an optimal image of all the structures of the internal and middle ear. The CT of the petrous pyramid is an HRCT scan, performed without a contrast agent, and the patient does not have to be on an empty stomach. It enables an assessment of the auditory ossicles, cochlea, hemispheric canals, internal and external acoustic ducts, pneumatisation of mastoid cells, congenital anomalies, posttraumatic lesions, and both benign and malignant growth processes. The quality of the obtained image in 2D and 3D reconstructions is a direct consequence of the scan parameters such as the thickness of the slice and bed slide, which depend on the class and quality of the slices of the scanner. Thanks to the spiral, multi-slice CT, the following methods of secondary processing of images have also become available: virtual endoscopy of the inner ear, multi-planar rendering of the data (MPR) and volume rendering (VR), which significantly increases the value of diagnostics of the petrous pyramids.


CT of the eye sockets– the advantage of the multi-slice scanners, in this case, is based on a significant decrease in the radiation dosage, which is of vital importance in CT scans of the eyeball area due to the risk of cataracts. Apart from this, the use of sub-millimeter slices, together with the CT of the petrous pyramids, provides a highly accurate analysis of posttraumatic injuries within the whole facial skeleton. With the exception of posttraumatic conditions and a search for foreign matter in the eye sockets, the scan is performed with the use of a contrast agent (thus the patient should be on an empty stomach). In non-traumatic cases, the CT is recommended only when the result of a routine USG is unequivocal. The CT scan enables an assessment of the neoplastic infiltration from the outside, metastases to the eyeball and extra ocular structures and primary cancers of the eyeball and other structures inside the eye sockets.


CT of the facial skeleton
– the scan is recommended in the assessment of dental processes of the upper and lower jaw and after injuries to the facial skeleton. The scan is performed without a contrast agent, contrary to the diagnostics of patients with neoplastic disease (primary and secondary cancers and infiltrations from the adjoining organs). During the scan the patient usually lies on the abdomen, with the head tilted backwards. The use of multi-slice CT and thin slices of the imaging affects the quality of the 3D rendering and enables a more accurate assessment of the bone structures, which is especially important in post-trauma conditions.


CT of the paranasal sinuses– the scan is to assess congenital lesions, post-traumatic and inflammatory conditions. It is performed using the HRCT method, which does not require the administration of contrast agents and is linked to low-dose radiation. Patients with suspicions of primary or secondary cancers in the sinuses are scanned with the use of a contrasting agent and in such cases they should present for the scan on an empty stomach. Despite various methods of data acquisition (patient’s position), the use of a multi-slice spiral CT makes it possible to obtain frontal, side and cross views with the use of multi-planar renderings (MPR).


CT Perfusion – thanks to the fact that spiral scanners have been introduced to diagnostics, with the CINE option (multiple scanning at the same level), a modern assessment of blood flow in the capillaries of an examined area is now possible. This method has been applied e.g. in the assessment of cerebral blood flow. It enables the imaging of the penumbra and ischemic areas before the formation of irreversible morphological lesions therein, namely myocardial infarction. The classic CT reveals the areas of infarction, without any opportunity for penumbra analysis. Together with an increase in the number of slices in computer tomography, there is an increase in the range of cerebral volume in which the blood flow is examined. It provides an opportunity for better assessment of the ischaemia and its range. CT Perfusion has also been introduced for diagnostics of tumours of the brain, liver, prostate gland and other organs.


CT of the neck– CT scans of the neck, larynx and nasopharynx are carried out in the diagnostics of organs located in the neck. These examinations should be done after the intravenous administration of a contrast medium, which should be performed before the patient has eaten. Imaging of the neck is performed to assess the lymph nodes, inflammatory and neoplastic infiltrations, and the relationship to the arterial and venous vessels, airways or salivary glands. The accuracy of the diagnostics of the larynx increases considerably with the use of secondary rendering such as 3D, MIP, MPR volume rendering and others, enabling a better imaging of the shape, assessment of the size and detection of lesions related to this organ.


Angiography (CT angiography)– this highly useful clinical examination has come about thanks to the introduction of the spiral CT, and its quality has continued to improve with the evolution of multi-slice technology. Technological progress has enabled the examination of vessels of increasingly smaller diameter. Nowadays multi-slice tomography scanners enable the scanning of such large anatomical areas as the arterial vessels of the lower limbs, hip arteries and the end portion of the abdominal aorta. To picture the blood vessels, the blood circulating therein must be mixed with a contrast medium; because it is necessary to administer a large amount of this medium (usually 2 or more ml/kg of body weight), non-ion based media are used in the examination, which decreases the risk of complications. Before the CT scan, a Doppler USG of the examined vessels is recommended, except for the pulmonary artery and patients with SAH. Apart from the routine assessment of cross views of the vessels, 2D and 3D renderings of the inside of the vessel, containing blood with the contrast medium, are an important element of the assessment of the CT angiography scan. The examination may concern, among others: cerebral vessels (searching for vascular malformations), cervical and spinal arteries (assessment of atherosclerotic lesions), abdominal vessels (narrowing of the main arterial trunks, especially renal trunks, in searching for causes of hypertension), pulmonary arteries (pulmonary embolism or its large branches), and thoracic and/or abdominal aorta (diagnostics of aneurysms).


CT of the abdominal cavity– computed tomography is one of the basic techniques for investigations of the abdominal cavity. It enables the assessment of the parenchymatous organs – the liver, spleen, pancreas, and kidneys. If the USG result is unequivocal, it is performed to confirm the diagnosis and to provide a differential diagnosis of primary and secondary neoplasms and benign lesions. Apart from this, the gall bladder and extrahepatic and intrahepatic bile ducts are also examined. This method makes it possible to check the range of inflammatory and neoplastic infiltrations within the stomach walls, small and large intestines, adrenals, and assess the likelihood of recurrence at the site of the removed tumour. The proper preparation of the patient is always required. The intestinal loops should be filled with a 1-2% water solution of iodine, ion-based contrast medium, which enables the differentiation of the intestinal interior, its wall, and structures adjacent to the intestines. Before the scan, the patient remains on an empty stomach for 5-6 hours. The amount of orally administered fluid and the time taken for the contrast administration depends on the indications for the examination. Thanks to spiral multi-slice computer tomography scanners, dynamic-multiphase scanning has nowadays become standard. Perfusion examinations in the liver and pancreas are something of a novelty.


Dynamic scan of the liver and/or pancreas– the procedure is performed to differentiate between metastases and vascular malformations of the liver and if neoplastic disease of the pancreas is suspected. It is based on a scan of these organs in both the arterial and venous phase (2-phase examination), and in an examination of the liver, and in the portal phase (3-phase examination). The chance of dynamic examinations has come about with the introduction of spiral machines, especially multi-slice ones (the scanner must "follow" the flowing of the contrast medium through the arterial, capillary and venous beds).

Indications for the CT of the liver:

  • Diagnostics of tumours: undifferentiated hepatic lesion, primary hepatic neoplasms, metastases
  • After a procedure: complications (haematoma, bile leakage. abscess), perfusion disorders
  • Vascular: portal vein thrombosis, anatomy of vessels (assessment before an operation/procedure),Osler disease
  • Other: abscess, injury
  • Quantitative measurements: haemosyderosis (iron content), volume of the liver and tumours

 


Virtual colonoscopy – CT colonography
– a procedure recommended as a screening test when colorectal polyps, post-inflammatory lesions, diverticulosis, and neoplasms are suspected, and in all patients with contraindications against the classic colonoscopy, which is a standard test in detecting and diagnosing diseases of the large intestine. Before introducing the virtual colonoscopy procedure into imaging diagnostics, the intestines could only be assessed when filled with a 1-2% solution of ion-based, iodine-based contrast media using a classic CT scan. Due to this, it was impossible to assess the thickness of the wall, any change in the position of the intestines or a change in the width of their lumen. A virtual colonoscopy enables the assessment of the interior surface of the intestinal walls. It can be done only on appropriate workstations, high performance computers, enabling an advanced 3D reconstruction with the use of Navigator software. Another prerequisite for obtaining a legible image of the inside of the intestine is the complete emptying of food residue from its lumen. The patient should be prepared as he would be for traditional colonoscopy. However, there is a chance that in the near future, contrast media will be available which will bind with the chyme and enable it to be singled out in the picture. The quality of this method is increasing with a shortened examination time due to peristalsis and the necessity of holding one’s breath. The examination can only be performed with the use of multi-slice tomography.


CT of the chest and mediastinum– the most frequent indications are the assessment of organs contained in the chest in benign and malignant neoplastic processes, both primary and secondary, and in chronic or atypical inflammatory diseases. Other groups of recommendations are an assessment of the range of infiltration in a neoplasm of the oesophagus, lesions of the mediastinal lymph nodes, pulmonary embolism, lesions post-radiotherapy, neoplastic infiltrations coming from the pericardium or heart and injuries to the chest. To obtain an intensive enhancement of the heart and large vessels in the mediastinum, the intravenous administration of a contrast agent is required, making it possible to differentiate pathological changes from the normal state of the organs. For selective assessment of the pulmonary tissue, a HRCT scan of the chest is performed without a contrast medium. The HRCT is recommended in the case of pneumoconiosis, systemic diseases of the connective tissue, interstitial pulmonary fibrosis, bronchiectasis and oedemas.

Indications for the spiral and multi-slice CT scan:

  • Diagnostics of tumours: tumours of the lungs and mediastinum, secondaries, assessment of a tumour (single tumour), assessment of tumour progression
  • Detection and quantitative assessment: occult inflammatory process,  breakdown, asbestosis, silicosis, oedema, bronchiectasis
  • Location preceding: biopsy, bronchoscopy, bronchoalveolar lavage, differentiation of lesions in the lungs from pleural lesions

High resolution computed tomography (HRCT) - Diffuse lung diseases:

  • Detection of discreet lesions in the parenchyma of the lungs
  • Morphological characteristics
  • Quantitative assessment of lesions in the parenchyma of the lungs
  • Location of the lung or bronchoalveolar lavage before an open biopsy


CT of the spinal canal
– A CT of the spinal canal is performed solely to assess the bony elements in posttraumatic lesions, neoplastic infiltrations or degenerative diseases of the facet joints of the spine. Pathologies of the intervertebral disc and surfaces of adjacent vertebral bodies act as another indication. Patients do not have to be on an empty stomach. Generally the scan does not require administration of the contrast medium.


CT of bones and/or joints– A CT of these organs covers two different methods of examination depending on the indications. The first group of indications consists of examinations performed without contrast media and aimed at an assessment of the bony structure in case of Paget’s disease, fibrous dysplasia, posttraumatic lesions or degenerative disease of joints, in the case of an ambiguous clinical and radiological picture in the plain X-ray image. The other group of indications, apart from the assessment of the bony structures, include pathologies of soft tissues around bones and inflammatory and neoplastic infiltrations, both those spreading from bones onto soft tissues and the other way round. The indications comprise benign and malignant cancers of bones and joints, an assessment of the range of cancerous infiltrations and their relationship to the marrow cavity and soft tissues and chronic and atypical inflammatory conditions of bones and joints. In such cases it is necessary to administer a contrast medium, and the patient should remain on an empty stomach. The CT multi-slice systems, besides the possibility of a detailed assessment of complicated fractures (thin layers, retro-reconstructions and 3D), are even able to produce high-quality images of soft tissues e.g. sacral ligaments, for which the examination of choice is magnetic resonance. Additionally, modern software makes it possible to put one picture on another, from various points of view, so as to calculate the angles, e.g. of anteversion, amongst others, which may be helpful when planning orthopaedic procedures.


CT of the small pelvis
– this examination is intended for an assessment of the urinary bladder in neoplastic processes, pelvic lymph nodes, and a range of neoplastic infiltrations in the reproductive organs, before elective surgery or irradiations or for an assessment of the likelihood of the recurrence of unclear USG results. A frequent indication in men is an examination of the range of neoplastic processes of the prostate gland and possible expansion of the neighbouring organs, with an unclear USG result. This examination, similarly to the abdominal CT, always requires the careful preparation of the patient before the scan, of course with the exception of those carrying injuries. The preparation is aimed at filling the intestinal loops with a 1-2% water solution of an iodine- and ion-based contrast agent, which makes it possible to separate the inside of the intestine from its wall and to separate the intestine from the adjacent structures. Before the examination the patient remains on an empty stomach for 5-6 hours. The total amount of fluid administered orally depends on whether this examination is combined with the abdominal tomography or is performed as a separate scan. Patients who undergo only the CT scan of the pelvis may alternatively have the contrast medium administered via the rectum.