Presentation on theme: "Mid Term Revision Directed Study 1 Dr Mohamed El Safwany, MD."— Presentation transcript:
Mid Term Revision Directed Study 1 Dr Mohamed El Safwany, MD.
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 . 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
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
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
The first spiral scan is acquired simultaneously with the beginning of the contrast injection, and therefore without any hepatic contrast enhancement
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
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
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.
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.
Optimization Of CT Scan Protocol In Acute Abdomen
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,
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)
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
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.
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 mm.
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
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
CT -HCC pre contrast
Arterial enhancement (central and early)
Washout on portal venous indicates fast flow
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
CT COLONOGRAPHY Dissection Strip, anus to caecum Endoluminal (for fun only) 800/40 window Axial to loops Orientation Overview
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
Incomplete air column -Excess fluidSupineProne Can rotate image volume to view as a Ba enema in 3D
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
Renal Vasculature Evaluation Using A Multidetector CT Scanner 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.
Scan ning 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 image acquisition parameters (60 cc after contrast). Further which a delayed acquisition (12/15 min after contrast injection) is done with 5mm slice and 5mm collimation to image the pelvicalyceal system, ureter and bladder. No oral contrast is used. Acquired images were axially reconstructed with overlapping slices and transferred to an imaging workstation
MIP reconstruction is the technique of choice for image presentation because it is able to produce angiography like images
REQUIREMENTS FOR CTA PATIENT PREPARATION ACQUSITION PARAMETERS CONTRAST MEDIUM ADMINISTRATION POSTPROCESSING TECHNIQUES
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.