Mid Term Revision Directed Study 1

1. Mid Term Revision Directed Study 1 Dr Mohamed El Safwany, MD.

2. Advanced tumor detection and characterization Taking vascularity and perfusion type into account, lesions such as hepatic adenomas, focal nodular hyperplasia and less-differentiated hepatocellular carcinomas, as well as endocrine metastases and sarcomas, will result in hyperattenuation. Metastases of other origins will show hypoattenuation with various temporal characteristics in the early arterial phase [6]. If a monophase and monoslice CT technique is applied, many of the hypervascular hepatic lesions will be completely invisible, but up to 30 % more lesions are detected in the early arterial phase compared with the portal venous phase

3. Acquisition of multiple perfusion phases • slice thickness 3.2 mm • reconstruction interval 1.6 • pitch 1.2 • gantry rotation 0.5 s • field of view 350–450 mm • 150–200 mAs

4. As the scanning process is usually initiated simultaneously with the beginning of an intravenous contrast injection of 120 ml of low osmolar, nonionic contrast agent at an injection rate of 5 ml/s, no bolus tracking techniques are necessary. Contrast agents with higher iodine concentrations (370–400 mg I/ml) may be advantageous in CT hepatic imaging, especially in the visual evaluation of the arterial phase detectability of hepatocellular carcinomas

5. The first spiral scan is acquired simultaneously with the beginning of the contrast injection, and therefore without any hepatic contrast enhancement

6. The second spiral liver scan, approximately 10 seconds after contrast initiation, usually shows moderate contrast enhancement of the abdominal aorta and the hepatic artery, without admixture of enhanced portal venous blood

7. The late arterial phase, acquired approximately 20 seconds after contrast initiation, leads to a clear depiction of the hepatic artery and its branches, due to a distinctive contrast enhancement

8. CT Angiogram • Quickly becoming the test of choice for initial evaluation of a suspected PE. • CT unlikely to miss any lesion. • CT has better sensitivity, specificity and can be used directly to screen for PE. • CT can be used to follow up “non diagnostic V/Q scans.

9. Pulmonary angiogram • Gold Standard. • Positive angiogram provides 100% certainty that an obstruction exists in the pulmonary artery. • Negative angiogram provides > 90% certainty in the exclusion of PE.

10. Optimization Of CT Scan Protocol In Acute Abdomen

11. Scan Protocols • core of every CT examination. • protocols should be appropriate for the clinical indication • should include all aspects of the exam such • positioning, • nursing instructions, • scan parameters( including radiation dose) • reconstruction/reformatting instructions,

12. Scanning parameters • multislice CT is better than single slice • MSCT : • –High quality • –Wider range of examination • –Thinner slices • –Shorter scan time • –Multiphases protocol • –Better reconstruction ( isotropic voxel)

13. Slice thickness: Acquire thins, reconstruct thick: Less noise • Scan coverage: scan length • Rotation speed: Keep fastest…for most regions to allow breath hold tech and more coverage

14. Increment • is the distance between the reconstructed images in the Z direction. • When the chosen increment is smaller than the slice thickness, the images are created with an overlap.

15. Increment • is useful to reduce partial volume effect, giving you better detail of the anatomy and high quality 2D and 3D post-processing . • can be freely adapted from 0.1 - 10 mm.

17. General Hints • Topogram : AP, 512 or 768 mm. • Patient positioning: Patient lying in supine position, arms positioned comfortably above the head in the head-arm rest lower legs supported. • Patient respiratory instructions: inspiration • Scout : AP and lateral

18. General Hints • Limit scan to intended anatomic area to cut dose by 10% • –Abdomen: • Just above diaphragm – Inferior pubic symphysis • –Chest: • Routine: Apex to adrenals • PE or benign clinical reasons: Apex to lung bases

20. CT -HCC pre contrast

21. Arterial enhancement (central and early)

22. Washout on portal venousindicates fast flow

23. HCC Summary • US - usually heterogeneous Usually HepB +ve with raised alpha FP • CT – C- low density C+A – central early contrast (high flow rate) C+PV – washout cf with liver – may have a capsule • MR – intracellular fat on T1 out of phase - similar perfusion characteristics to CT

24. CT COLONOGRAPHY Dissection Strip, anus to caecum Endoluminal (for fun only) Orientation Overview 800/40 window Axial to loops

25. Advantages / disadvantages • Sensitivity and specificity is of the order of 90 % for 10 mm polyps. • Easy, quick and well tolerated. • Beats barium enema hands down. • Safer than optical colonoscopy • Approx. half the price of optical colonoscopy • No intervention possible as in optical Cy • At present for “Ba enema” indications, but is likely to be used for screening in future. • Radiology manpower training required. • Radiation dose equivalent to Ba Enema

26. Incomplete air column -Excess fluid Supine Prone Can rotate image volume to view as a Ba enema in 3D

27. Diverticular disease

28. CT ENTEROCLYSIS Jejunum often thick-walled Can evaluate bowel wall due to negative contrast in lumen and IV contrast in wall. Evaluates stomach well also Plus standard CT Reserved for older patients due to radiation dose

29. Renal Vasculature Evaluation Using A Multidetector CTScanner The technique consists of image acquisition, image processing and finally image display. As regards the image acquisition the following was our protocol: 100cc of iodinated contrast was injected at 2.5 ml/sec, using automated techniques e.g.: care bolus (for beginning of acquisition). Images that were obtained were of 1.25 mm slice thickness with 1mm slice collimation.

30. Scanning is done from the twelfth dorsal or the first lumbar vertebral level to the level of the pubic symphysis. After the arterialphase, a venous phase is followed using same imageacquisition parameters (60 cc after contrast). Furtherwhich a delayed acquisition (12/15 min after contrastinjection) is done with 5mm slice and 5mm collimation toimage the pelvicalyceal system, ureter and bladder. Nooral contrast is used. Acquired images were axiallyreconstructed with overlapping slices and transferred toan imaging workstation

31. MIP reconstruction is the technique of choice for image presentation because it is able to produce angiography like images

32. REQUIREMENTS FOR CTA • PATIENT PREPARATION • ACQUSITION PARAMETERS • CONTRAST MEDIUM ADMINISTRATION • POSTPROCESSING TECHNIQUES

33. PARAMETERS • USUALLY ROUTINE CT PRECEDES A CTA EXAM. THE ROUTINE EXAM IS USED AS A REFERENCE SCAN HELPING TO DETERMING THE SCANNING RANGE IN CTA.

34. SLICE THICKNESS SPATIAL RESOLUTION SLICE THICKNESS

35. CEREBRAL CTA ABDOMINAL CTA THORACIC CTA 1MM (LOWER mA) 3MM 3MM SLICE THICKNESS

36. PITCH SPATIAL RESOLUTION SPIRAL PITCH

37. TWO TECHNIQUES TO REDUCE MOTION ARTIFACTS IN CARDIAC CT • PROSPECTIVE TRIGGERING • RETROSPECTIVE GATING

38. 3-D VISUALIZATION TOOLS IN CTA • MPR • MIP • SSD • VR • CINE

39. Good Luck