Items tagged “ct”
25 results found
Article
Capillary hemangioma of the orbit
Capillary hemangiomas of the orbit, also known as strawberry hemangiomas, on account of its coloring, or orbital infantile hemangiomas, are the most common orbital tumors of infancy, and unlike orbital cavernous hemangiomas, they are neoplasms rather than vascular malformations.
Clinical presen...
Article
Fetal dosimetry
NB: Please consult original article(s) and discuss with your local radiology department/radiation physicist before making any clinical decision.
Although radiation exposure to the gravid uterus is to be avoided whenever possible, and only deliberately performed after careful weighing up of the ...
Article
Tube arcing
Tube arcing occurs when there is a short-circuit within the tube, typically from the cathode to the tube envelope. The result is a temporary loss of x-ray output and a localized artifact.
A number of causes of tube arcing are recognized 1:
insulator surface flashover
insulator breakdow...
Article
Striated nephrogram
Striated nephrogram is a descriptive term indicating the appearance of alternating linear bands of high and low attenuation in a radial pattern extending through the corticomedullary layers of the kidney on iodine-based intravenous contrast-enhanced imaging.
It is important to know that a simil...
Article
McAfee classification of thoracolumbar spinal fractures
McAfee classification of acute traumatic spinal injuries is one of a number of thoracolumbar spinal fracture classification systems and based on the three-column concept of the spine (of Denis). It requires CT for an accurate assessment.
Usage
The McAfee classification uses terminology that is...
Article
Contrast media extravasation
Contrast media extravasation (CMEV) refers to the leakage of intravenously-administered contrast media from the normal intravascular compartment into surrounding soft tissues; it is a well-known complication of contrast-enhanced CT. It can also occur in MRI, but the complications are rare given ...
Article
Pitch (CT)
Pitch (P) is a term used in helical CT with two terminologies depending on whether single slice or multislice CT scanners are used 1-3.
Single slice CT (SSCT)
The term detector pitch is the table distance traveled in one 360° gantry rotation divided by beam collimation 2.
For example, if the ...
Article
Pyonephrosis
Pyonephrosis is a term given to an infection of the kidney with pus in the upper collecting system which can progress to obstruction.
Pyonephrosis may be suspected when the clinical symptoms of fever and flank pain are combined with the radiologic evidence of urinary tract obstruction 1. Debris...
Article
Tuberculous peritonitis
Tuberculous peritonitis is a form of extrapulmonary tuberculosis affecting the peritoneum. It is frequently seen in association with other forms of gastrointestinal tuberculosis 6.
Epidemiology
Tuberculosis is usually confined to the respiratory system but may involve any organ system 1. Extra...
Article
CT stair-step artifact
The CT stair-step artifact is found in straight structures which are oriented obliquely with respect to movement of the table and appear around the edges of sagittal and coronal reformatted images when wide collimations and non-overlapping reconstruction intervals are used.
It is also seen in c...
Article
Iodinated contrast-induced thyrotoxicosis
Iodinated contrast-induced thyrotoxicosis is rare and may occur in patients with pre-existing thyroid disease and through complications of thyrotoxicosis (e.g. cardiac arrhythmia) may be fatal. Patients with a normal thyroid gland are unaffected.
Patients with existing thyrotoxicosis should no...
Article
Meglumine iotroxate (Biliscopin)
Meglumine iotroxate (BiliscopinTM) is an iodinated, intravenous contrast agent that is preferentially excreted into the biliary tree and is used in CT intravenous cholangiography.
The typical dose is 100 mL Biliscopin (105 mg meglumine iotroxate/mL; 5.0 g iodine), which is administered via slow...
Article
Hounsfield unit
Hounsfield units (HU) are a dimensionless unit universally used in computed tomography (CT) scanning to express CT numbers in a standardized and convenient form. Hounsfield units are obtained from a linear transformation of the measured attenuation coefficients 1. This transformation (figure 1) ...
Article
Helical CT image acquisition
Helical (a.k.a. spiral) CT image acquisition was a major advance on the earlier stepwise ("stop and shoot") method.
With helical CT, the patient is moved through a rotating x-ray beam and detector set. From the perspective of the patient, the x-ray beam from the CT traces a helical path. The he...
Article
Lung hyperinflation
Lung hyperinflation is a common feature of patients with chronic obstructive pulmonary disease (COPD). It is also linked to aging and other chronic diseases that cause airflow obstruction.
Pathology
The airflow limitation during expiration is produced by two factors:
destruction of the lung p...
Article
CT fluoroscopy
Computed tomography (CT) fluoroscopy combines the conventional advantages of both CT and fluoroscopy and has an important role in image-guided interventions where real-time imaging is required.
Historically, fluoroscopy was the main image guidance tool for interventional radiology procedures. T...
Article
Image reconstruction in CT fluoroscopy
Image reconstruction in CT fluoroscopy requires the computer to provide very fast reconstructions of images in order to provide immediate and accurate spatial and anatomical feedback during a procedure. This is achieved by:
use of a small reconstruction matrix – e.g. 256 x 256 (compared with co...
Article
Radiation dose considerations in CT fluoroscopy
Consideration needs to be made to the radiation dose to both the patient and radiologist in CT fluoroscopy, given the relatively high and continuous radiation exposure involved.
Radiation exposure to the patient
The patient surface dosage may range between 2 and 10 mGy/sec, with exposure times...
Article
Kernel (image reconstruction for CT)
The kernel, also known as a convolution algorithm, refers to the process used to modify the frequency contents of projection data prior to back projection during image reconstruction in a CT scanner 1. This process corrects the image by reducing blurring 1. The kernel affects the appearance of i...
Article
Cone beam effect
Cone beam effect artifacts are seen in multidetector row CT (cone beam CT) acquisitions 1. Modern CT scanners use more detector arrays to increase the number of sections acquired per rotation. This causes the x-ray beams to become cone-shaped as opposed to fan-shaped 2. As a result instead of co...
Unable to process the form. Check for errors and try again.