BIOE 220/rad 220 Review session 7

1. BIOE 220/rad 220 Review session 7 March 13, 2012

2. What We’ll Cover Today • Discussion of the final review • General questions? • Common issues on hw, and questions we’ve received • Cranial nerve review • Time for more questions

3. Slice Interleaving • On the homework, you had a problem where you imported every 18th frame of some data • Many students thought that we were looking at every 18th frame • If you looked at the other frames, you’d see that they were images of other slices • During typical scan, we have a TE that is much shorter than TR • That “dead time” can be used to acquire other slices in Z • As long as only one slab is excited at a time, we can collect up to floor(TR/TE) slices concurrently

4. MTT • On the homework, there was a problem about mean transit time • During lecture, mean transit time was defined as the average amount of time for blood to flow through a voxel • In the homework, we asked the amount of time to reach half maximum CBV • If you read Buxton, you’ll find that there are two different meanings for MTT, used interchangeably and ambiguously • In Greg’s lecture, MTT referred to the amount of time to move through a voxel • In the homework, MTT referred to the average amount of time for the bolus to reach the site • Bolus injection occurred at time zero on the HW, which probably should have been specified explicitly

5. Using bolus signal change to find CBV • In the last couple homeworks, we’ve asked you to find the ratio of CBV between two tissues based on the area under the signal deflection • If the signal remained flat, it would mean that there was no contrast passing through • By measuring the total effect of the contrast on the signal as it passes through, we infer the amount of contrast that passed through • This allows us to estimate the relative blood volume for two regions responding to the same bolus, but it does not give us an absolute measure of CBV

6. How to tell if fat suppressed • As Kim said in class, unless fat suppression is used, fat will appear bright (or very bright) in each type of MR image • In the head, we see fat outside the skull below the skin (subcutaneous fat) • In images of the spine, fat will appear under the skin, posterior to the spine (at the edge of the image) • May also see fat in bone marrow, particularly in older patients • If you see bright fat under the skin, suppression was not used, otherwise it was used • Chemical saturation can be used to suppress fat in any of our sequences, STIR can only get T2 weighting (why?_

7. How to tell if there is contrast • Look for vessels • Whenever we discuss MR contrast in class, we’re referring to gadolinium in the vasculature • If vessels show up very bright, it is usually a contrast image • In the head, superior sagittal sinus showing up bright is an obvious indication of contrast • Some sequences will use flow of vessels to make them show up bright. If the rest of the image appears normal but vessels are bright, then contrast was used. If the rest of the image is suppressed, we may be looking at non-contrast enhanced angiography • In CT, don’t confuse calcified structures (choroid plexus in ventricles, pineal gland) for contrast in vessels

8. How to Identify Modality - Review yes T2 Spin Echo Is CSF very bright? Are the bones bright? no MRI no yes Are CSF and Gray Matter the Same Brightness? yes Are we seeing a projection, or a slice? Proton Density Slice Projection CSF is dark Is gray matter brighter than white matter? CT Radiograph no T1 Weighting yes FLAIR (T2 contrast, dark CSF)

9. Imaging modality in the spine? • Some people have asked how to recognize the MR imaging modality in the spine • Easiest landmarks are CSF around spinal cord and fat under skin • If CSF is bright, we’re T2 weighted, if CSF is dark we have T1 weighting • If fat is bright, no fat suppression was used, if fat is dark then it was suppressed (either chemical saturation, or STIR) • (As far as I can tell, we don’t use FLAIR on the spine) • If you see bright areas scattered through the image (triangles in lower vertebra in the homework) then contrast was probably used • If you’re given an axial image of the spine, you should be able to recognize T1 versus T2 by looking at the gray and white matter in the column • (Unlike in the brain, gray matter inside, white matter outside)

10. CRANIAL NERVES!!!!! SUPER FUN YAY

11. Cranial nerves • Olfactory • Optic • Oculomotor • Trochlear • Trigeminal • Abducens • Facial • Vestibulocochlear • Glossopharyngeal • Vagus • Spinal Accessory • Hypoglossal

12. Cranial Nerves

13. Cranial Nerves

15. Eye Muscles Pupils equally round and reactive to light and accommodation : PERRLA - CN II and III in tact.

16. Tongue Muscles • There are many tongue muscles, and CN XII innervates all of them (except one that is innervated by CN X). • Genioglossus is primarily responsible for sticking your tongue out. It attaches on the mandible in the center of your chin and joins the rest of the tongue muscles.

17. Tongue Muscles

18. Tongue Muscles

19. CRANIAL NERVE EXAM! • Smell (I), sight (II), eye muscles (III, IV, VI), hearing (VIII), biting down (V), making faces (VII), neck rotation (XI). • Touch (V), taste (VII, IX), pharyngeal muscles (IX, X), stick out the tongue (XII)