Transient Interruption of Contrast

NOVEMBER 2016 | volume 54 number 2 THE SOUTH AFRICAN RADIOGRAPHER peer reviewed CASE REPORT

Case report: Transient interruption of contrast

E Magaya Dip D Rad (UZ), B Sc Special Honours in D Rad (NUST), Dip Ultrasound (ECUREI - Uganda) Principal radiographer, Baines Imaging Group, Harare, Zimbabwe

Abstract Transient interruption of bolus contrast is a physiologic artefact due to a poor mixture of blood and contrast material. It is en- countered when performing computed tomography pulmonary angiograms (CTPA). A working knowledge of this phenomenon is crucial to avoid a misdiagnosis of pulmonary embolism. A relatively high percentage (5-6%) of CTPA has been deemed in- conclusive or technically insufficient due to poor contrast enhancement of the pulmonary arteries, which affects 40% of CTPAs. This case report describes this phenomenon and the setting in which it occurs. The patient’s clinical history, radiological findings, appearance, and possible countermeasures, are described. Keywords Bolus contrast, artefact, computed tomography, pulmonary angiograms, pulmonary embolism.

Case report tient that further scans were needed. For terruption to the flow of contrast into the the repeat scan, the patient was instruct- pulmonary trunk.[3] A female inpatient geriatric was referred ed not to take a deep breath prior to the It is believed that when a patient inspires to the CT department. She complained scan but to just hold her breath following deeply, just before scanning begins, it re- of chest pains, shortness of breath and normal breathing. The scan showed that sults in either increased venous return of had reduced saturations of 83% (normal the pulmonary arteries were opacified unopacified blood from the inferior vena above 90%). A CT pulmonary angiogram (Figure 3). In this instance there were no cava or reduced delivery of iodinated con- was requested to rule out pulmonary em- obvious filling defects typically found on trast from the superior vena cava.[4] Un- bolism. The examination was treated as CTPA (see Figure 4). an emergency since pulmonary embolism opacified blood entering the right atrium is one of the leading causes of acute car- Discussion dilutes the contrast column coming from diovascular disease, after myocardial inf- the superior vena cava; the result is seen arction and stroke, which may be fatal.[1] Transient interruption of contrast (TIC) is as a transient decrease in attenuation.[4] Urea and creatinine levels were within the a flow artefact that consists of relatively After inspiring deeply patients tend to per- normal range. Informed consent was ob- poor contrast opacification in the pul- form the Valsalva manoeuvre involuntarily tained from the patient. It was ascertained monary arteries while there is optimum when asked to hold their breath prior to that the patient had no known allergies to contrast enhancement in the aorta and scanning. This can cause an increase in in- iodine. A pre-contrast scan was not per- superior vena cava.[2] This phenomenon trathoracic pressure leading to decreased formed. The contrast enhanced sequence is unwelcome for many reasons, mostly blood filling of both ventricles, resulting in was obtained after administration of 80ml because it may result in emboli being ob- reduced cardiac output and delaying peak of Jopamiron (Iopamidol) 370mgI/ml in- scured within the insufficiently opacified contrast enhancement of the pulmonary jected at a rate of 4ml/s followed by 20ml pulmonary artery leading to a misdiagno- arteries.[5] In other cases the presence of of normal saline. The contrast was inject- sis. This then means that it is a phenom- a patent foramen ovale causes a transient ed using a Medrad Stellant injector pump. enon, which all CT radiographers should intra-cardiac right-to-left shunt with deep The scan and view scan was positioned a be aware of, as it has potentially devastat- inspiration.[4] Patients with large areas of centimetre below the carina. The contrast ing consequences. active lung disease, like atelectasis, also was automatically tracked using Surestart tend to have lower contrast enhancement Further imaging may be needed to ex- until 160 Hounsfield units (HU) had been in pulmonary arteries. A reason for this clude thrombus hidden in the poorly en- reached, after which it automatically trig- could be regional vasoconstriction, which hanced vessels.[2] A repeat CT scan means gered scanning. Before the start of the leads to increased pulmonary vascular increased ionising dose to patients, and scan the patient was instructed to take a resistance and therefore decreased blood adds to the costs of the examination. An- deep breath and hold her breath. An im- flow in the pulmonary arteries.[5] mediate review of the CT scan was done other disadvantage is that patients may on the console monitor. It demonstrated become anxious. So how does this arte- Literature suggests that TIC is more preva- contrast within the superior vena cava, fact come about? Instructing patients to lent in pregnant patients than the general ascending thoracic aorta and descending take a deep breath and hold their breath population, ranging from 5.6% to 35.7%.[6] aorta, but with an unenhanced pulmonary immediately prior to scanning, as what This is because of the haemodynamics trunk (see Figures 1 and 2). A radiologist occurred during this CTPA examination, effects of pregnancy which include an reviewed the scan and informed the pa- has been reported to result in transient in- increase in cardiac output, total vascular

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Figure 1. A contrast-enhanced axial CT image of the thorax showing Figure 2. A contrast enhanced coronal CT image of the same patient the superior vena cava (bottom right arrow, white outline), ascending as above shows the superior vena cava (short grey arrow, on the aorta (top right arrow, white outline) and descending aorta (bottom right) and ascending aorta (top left arrow) opacified with contrast left arrow, white outline) opacified with contrast while the pulmonary while the pulmonary trunk (bottom left white arrow) is not opacified. trunk is relatively unenhanced (top left grey arrow, black outline).

Figure 3. A CT axial scan of the thorax in the same patient showing Figure 4. A CT axial scan of the thorax in a different patient showing opacification of the main pulmonary trunk (top left arrow, white positive saddleback pulmonary emboli. The pulmonary trunk is outline) and pulmonary arteries (right black arrow showing the opacified which allows easy identification of the emboli against the right pulmonary artery and the bottom left arrow, thick grey outline, white background of contrast (both arrows, left and right). showing the left pulmonary artery) after breathing normally during the scan. resistance, heart rate and plasma volume. case report, had a better outcome. The used as the optimal protocol for pulmo- These hemodynamics effects lead to dilu- breathing instructions should be easy to nary artery imaging. The drawback to this tion of the contrast bolus and an increase understand as much as possible. Instruc- protocol is that it suffers inferior parenchy- in inferior vena cava pressure, which can tions such as ’stop breathing’ or ’hold your mal enhancement and should be reserved [6] give rise to TIC. breath’ appear most appropriate while for failed inspiratory breath-hold CTPA.[1] Scanning with the patient breath-holding the automatically generated ’take a deep In pregnant patients, with suspected pul- [1] at ease was shown to have a beneficial breath in and hold it’ should be avoided. monary embolism, a pulmonary protocol effect of improving contrast density in To reduce inspiration and breath-holding optimised for use in pregnancy include a pulmonary arteries therefore improving associated artefacts some authors have high flow rate of contrast (in the region diagnostic image quality.[5] This could ex- promoted expiratory CTPA. They conclud- between 5 and 7ml/s), a high volume of plain why the second examination, in this ed that that expiratory scanning could be contrast and shallow held inspiration

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Conclusion References Computerised tomography pulmonary an- 1. Coulier B, Van den Broeck S. A case of 4. Bernabé-García J.M, García-Espasa C, Are- giography remains the gold standard for massive transient reduction of attenu- nas-Jiménez J et al. Has “respiratory coach- diagnosing pulmonary emboli.[6] One of ation of iodine contrast bolus during ing” before deep inspiration an impact on computed tomography pulmonary angi- the incidence of transient contrast interrup- the major artefacts, which hinder diagnos- ography: Why and how to avoid it. J of tion during pulmonary CT angiography? In- tic accuracy of CTPA, is the flow-related the Belgian Society of Radiology 2013; sights Imaging 2012;. 3(5):505-511. one called transient interruption of con- 96(5): 304-7. trast (TIC). Having a working knowledge 5. Paper S., Lau K.K., Li J, Ardley N, Lau T. 2. Wittram C, Maher CMM, Yoo AJ et Breath-hold at ease : a method of improv- of this artefact should enable CT radiog- al. 2004. CT angiography of pulmo- ing the diagnostic quality of CT pulmonary raphers to reduce indeterminate CTPAs. nary embolism: diagnostic criteria and angiogram. Poster presented at: European This would lead to increased confidence causes of misdiagnosis. RadioGraphics Congress of Radiology; Mar 2012 1-5; Vi- in reporting by radiologists and ultimately 2004; 24 (5): 1219-1238. enna, Austria. [5] better patient management. 3. Lloyd S., Sahu A.,Riordan R. Diagnosis 6. Ridge C.A., Mhuircheartaigh JN, Dodd of pulmonary embolism by computed JD, Skehan S.J. 2011. Pulmonary CT an- Acknowledgement tomographic pulmonary angiography giography protocol adapted to the hemo- with and without optimal contrast en- dynamic effects of pregnancy. AJR 2011; Ethics permission to write this case study hancement : a prospective single centre 197(5):1058-1063. was obtained from the head of the radiolo- audit. Hong Kong J of Rradiology 2012; gy department and the chief radiographer. 15: 162-169.