|Year : 2018 | Volume
| Issue : 11 | Page : 905-907
A mysterious case of unusual computed radiographic imaging artefacts: A clinician's dilemma
Harihar Vishwanath Hegde1, IK Annie2, Shyamsundar K Joshi2, Swathy S Iyengar1
1 Department of Anaesthesiology, SDM College of Medical Sciences and Hospital, Dharwad, Karnataka, India
2 Department of Radio-Diagnosis, SDM College of Medical Sciences and Hospital, Dharwad, Karnataka, India
|Date of Web Publication||2-Nov-2018|
Dr. Harihar Vishwanath Hegde
Department of Anaesthesiology, SDM College of Medical Sciences and Hospital, Dharwad- 580 009, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Hegde HV, Annie I K, Joshi SK, Iyengar SS. A mysterious case of unusual computed radiographic imaging artefacts: A clinician's dilemma. Indian J Anaesth 2018;62:905-7
|How to cite this URL:|
Hegde HV, Annie I K, Joshi SK, Iyengar SS. A mysterious case of unusual computed radiographic imaging artefacts: A clinician's dilemma. Indian J Anaesth [serial online] 2018 [cited 2018 Nov 15];62:905-7. Available from: http://www.ijaweb.org/text.asp?2018/62/11/905/244830
| Introduction|| |
Imaging artefacts in computed radiography (CR) images can at times pose dilemmas and a clinician should seek the opinion of the radiologist in such a scenario.
| Case Report|| |
A 36-year-old woman, married for 14 years was admitted with history of headache, giddiness and forgetfulness for 4 months, and difficulty in walking for 2 days. She had never conceived and her last menstrual period was 15 days ago. On examination, the patient had an exaggerated right knee-jerk reflex and unsteady gait. Computed tomography showed a left parieto-occipito-temporal glioma with subfalcine and uncal herniation. Pregnancy test was not performed as the husband and wife were sure about the menstrual history. The potential for conception in the intervening period after the last menses, perioperative risk of miscarriage and teratogenicity were explained. She underwent an emergency craniotomy and excision of the tumour successfully under general anaesthesia. A right subclavian central venous catheter (CVC) was inserted intraoperatively. A routine chest radiograph obtained postoperatively to confirm the CVC position revealed the outline of a foetus apparently lying within the patient's abdomen [Figure 1].
The menstrual history was reconfirmed from the husband. Close examination of the radiograph revealed soft tissue outline of a foetus lying transversely within the patient's abdomen with the foetal head to the right side facing cranially, limbs stretched out and the foetal back oriented caudally. We consulted a radiologist for clarification of the radiograph. Further investigation revealed positive history that the chest radiograph of this patient was preceded by a previous exposure of the same imaging plate (IP) for a radiograph of a stillborn foetus. Therefore, the image of the foetus was an artefact in the chest radiograph of this patient.
| Discussion|| |
The chest radiograph revealed a few artefactual shadows which may confuse clinicians, but their occurrence can be explained by understanding the principles of image formation in CR. The CR process [Figure 2], image freely available on the internet] occurs in a series of steps that begin with the IP absorption of the X-rays transmitted through the patient following an exposure. The energy transferred to the photostimulable phosphor material of the IP causes excitation of its electrons, raising them to a higher energy state in the conduction band where they travel freely till they are trapped in a centre called the “F-center.” These trapped electrons constitute the latent image. On scanning the IP with a focussed red laser beam the stored latent image is released in the form of visible light photons. This emitted light is then captured and converted into electric signals, processed, digitised and then displayed as a digital image.
All the trapped energy may not be released on one reading and this residual energy may be released on ensuing exposures of the next patient. To avoid this, information of the residual latent image must be erased. This is done by exposure of the IP to an intense fluorescent light for about 10–15 s, which removes the electrons that were remaining in the “traps” without stimulating further trapping of electrons. Sometimes, failure of the CR reader to erase the residual latent image from the plate occurs despite exposing the plate to intense light. These unerased latent images are less dense and appear as a background in the subsequent radiograph taken with the same IP resulting in an artefact called the “ghost” artefact. This can be avoided by delaying the subsequent exposure for at least 60 s and at times as long as 15 min. In case a high radiation dose exposure is suspected, the plate must be set aside for at least 24 h to ensure fading of the residual image, followed by erasure and reloading.
Three different types of artefacts are seen in this radiograph. The first artefact (“ghost” artefact) is the magnified soft tissue outline of a foetus lying transversely seemingly within the patient's abdomen with non-visualisation of the foetal skeleton. The second artefact seen in the lower half of the radiograph is the aliasing or moiré pattern which is caused by low-frequency grid patterns in the digital image. IP's are sensitive to scatter and hence grids are primarily used in CR imaging to reduce scatter. However, the right grid frequency needs to be selected as grids with low line rate will result in the aliasing/moiré artefact especially when the grid lines are parallel to the plate reader's scan lines. The third artefact is the bright linear horizontal band overlapping the lower chest extending across the chest wall on either side. These lines are caused by foreign materials like dust on the light collector of the CR reader.
| Conclusion|| |
With the growing use of the computed and digital radiography, anaesthesiologists, especially those working in intensive care units and emergency rooms, may encounter clinical scenarios requiring urgent interpretation of radiographic images. These clinicians need to be aware of the radiographic imaging artefacts that can have immediate diagnostic and therapeutic implications. This image serves as an example of the different forms of imaging artefacts that can compromise radiographic interpretation.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]