Introduction to abdomeno-pelvic CT

There are many types of CT devices according to the slice thickness they produce. - The thinner the thickness of slices the better resolution and details of images we can get. e.g. high resolution CT is a type of nonenhanced CT used to view interstitial lung diseases.

Uses of CT in elective cases Staging of tumors As Further investigation for incidental findings on other imaging techniques. For bone fractures it’s better to use CT CT guided procedures.

Uses of CT in emergency cases PE protocol. RTA (to know if there’s vascular injury). In neurology to know the type of strokes and if there’s hemorrhage. i.e. to differentiate hemorrhagic from non-hemorrhagic strokes

We have to have a detailed history of the patient to be in the safe side: - So we should ask about pregnancy (CT is very risky in the first trimester) and should warn the patient about these risks. - We should know if he has any allergy (to any drugs; specifically to any contrast agents), if he is allergic we should look for safer maneuvers but if we are obliged to use that contrast we should prepare him by giving pridnesolone tablets 1 day before the scan. Now if he said that he doesn’t have any allergy and during the scan he developed allergic reaction we should have an emergency set to deal with the situation (hydrocortison, antihestamine …etc).

Steps for Routine CT abdomen-pelvic scan: 1- fasting 6-8 h in adults, 4 h in children “missed meal”. 2- oral contrast; 1 L over 1 hour before scan 3- IV contrast. 4- scanning Put in mind; Routine abdomen-pelvic CT scan needs oral and IV contrasts.

1. fasting 1- oral contrast.(most important ) to prevent nausea and vomiting and to make the lumen as clear as possible 2-prevent aspiration if intubation in need , and lead to chemical pneumonia 3- frequent vomiting..

2- NICM “nonionic contrast media” No contraindication 2. Oral contrast: 1- gastrografin “iodinated”may lead to aspiration (chemical pneumonitis) pulmonary edema 2- NICM “nonionic contrast media” No contraindication Very safe in all cases, available and cheap. .

Oral contrasts are diluted in water or juices and we tell the patient to drink it over hour before scan Barium can be used in very diluted suspension but we don’t use it routinely (not like in flouroscopy) because it’ll give hyperdense field that will hide the mucosa, surrounding structures and lesions we are looking for so it’ll cause sever artifact

3. IV contrast: We use NICM, it is contraindicated as an IV contrast in; Renal failure; It is important to have recent KFT (one month at maximum) to avoid contrast-induced nephrotoxicity. If the patient has high creatinine then look for other modalities. If the patient undergoing hemodialysis do CT before hemodialysis. Allergy drugs (penecilline, cephalosporine), food (Iodine containing foods like egg, fish …etc). And previous allergy to contast. we may obercome this problem by the use of Hydrocortisone

Route of IV contrast i.V upper arm. svc Rt side of heart lung left side of heart body arteries (till this point is the arterial phase) portal system liver  systemic venous (till this point is the routine phase) excretion of contrast via kidneys. The idea here is about the scanning time. This time is fixed according to the study I do .

Route of IV contrast Three phases: 1-Arterial phase. 25 sec 2-Porto-venous phase. 40-60 sec 3-Delayed.>2-5 min Routine abdomen-pelvic CT scan is taken in porto venous. Angio CT arterial Delayed: ureter injury, CT urography, UGS, liver lesion.

Route of IV contrast - These times are measured through several studies. - As an example, the arterial time was measured to be 25 sec so after 25 sec the contrast will be outside the arteries. I can still see the arteries and study them but it will not be clear and the contrast will be very faint. - The idea about taking oral and IV contrast is to cover all the possibilities and to obtain full picture of anatomy like if we are studying the small bowel we don’t know where is the pathology so we give oral to see the lumen and IV to see the wall, mucosa … etc. - IV contrasts are mainly for solid organs like liver, spleen, kidneys, blood vessels, lymph nodes.

protocols 1. Routine  abdomen & pelvis oral & IV contrast porto venous. 2. Stone protocol abdomen pelvis without oral or IV contrast because the contrast will give me hyperdense field and the stone is already hyperdense so we will not be able to discriminate the stones. 3. Liver protocol without ( without IV contrast , to see if there is calcification and base line for enhancement ) + triple phases (arterial – to see angiogenesis- , PV & delayed) .

4. Adrenal protocol without + PV & delayed But in adrenal we need more delay (15 min ) due to less perfusion 5. pancreatic protocol  without + arterial , PV

- Routine means that in any elective case we do the scan using oral and IV contrast in the porto venous route. - The Idea about protocols is to differentiate between different lesions (malignant, benign, cystic, abcess …etc). - Every lesion has unique behavior regarding the contrast (uptake, washout). Malignant: rapid uptake and rapid washout - Benign: delayed uptake. Simple Cysts: will not uptake any contrast

Important notes: + abdomen & pelvis CT routinely from base of lung to pelvis , needs oral & IV contrast & scanning at PV phase. +clinical data is important to determine the protocol. +Some times You can modify the protocol according to the patient’s condition & pathology.

Now the Dr is talking about images in CT abdomen and pelvis Atlas Now the Dr is talking about images in CT abdomen and pelvis Atlas. Most questions on abdomeno-pelvic CT will come from Atlas images.

Azygos and hemiazygos veins are important and come in the exam Azygos and hemiazygos veins are important and come in the exam. You should know the structures piercing the diaphragm and at which level they pierce 1- IVC: T8 2- esophagus: T10 3- aorta: T12

Branches of aorta: 1- celiac trunk: T12 2- superior mesentric artery: L1 3- inferior mesentric artery: L3 Bifurcation of aorta at L4 union of IVC at L5

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