Overview of medical imaging: Focusing on Neuroimaging

Medical imaging Using the Electromagnetic Spectrum Sound waves Visible light X-ray, Fluoroscopy, CT, & Angiography gamma rays - PET (positron emission tomography) Radio waves from nuclear spin – MRI Sound waves - ultrasound

(could use photon picture b/c wave-particle duality) Electromagnetic wave (could use photon picture b/c wave-particle duality) one wavelength

Wave Particle duality of electromagnetic radiation

Electromagnetic Spectrum

Guiding Questions How does the energy interact with tissues? What is the energy used? How does the energy interact with tissues? How is the image produced? What is represented in the image?

Electromagnetic Spectrum Visible Electromagnetic Spectrum

Visible Endoscopy Laparoscopy - ovary

X-RAYs Advantages of X-Ray Disadvantages Roentgen : 1895 Discovered X-rays 1901 Nobel Prize Advantages of X-Ray cheap fast good diagnostic value for many things Disadvantages ionizing radiation - contrast is just density differences

Electromagnetic Spectrum X-RAYs Electromagnetic Spectrum

Roughly Proportional to mass How X-rays work Simple Fit Number of protons Roughly Proportional to mass

X-ray Radiography - 2D (ie Chest) Advantage very fast high resolution Disadvantage ionizing radiation xray contrast

X-ray Radiography - 2D 100KVp

X-ray Radiography - 2D Compton Scattering (Photoelectric effect) [everything going digital now]

Low energy X-ray b/c all tissue Bone healing study on rats X-ray Radiography - 2D Mammography Low energy X-ray b/c all tissue Bone healing study on rats

“Pretty pictures, but they will never replace radiographs” –Neuroradiologist 1972 (X-ray) CT – computed tomography – 3D Godfrey Hounsfield 1972 (nobel prize 1979) Advantage high resolution 1mm x0.4mm x 0.4mm 3D Disadvantage ionizing radiation xray contrast Axial - abdomen Axial - head

What is tomography Red dots are areas of high density Peaks are number of Xrays absorbed (note : normally would do axially and not sagittally)

Why is water in brain dark compared to brain tissue? (X-ray) CT – computed tomography – 3D Axial - head Axial - abdomen Substance HU Air -1000 Fat -120 Water Muscle +40 Bone +1000 Why is water in brain dark compared to brain tissue? Houndsfield Units

CT: What does the image represent? (X-ray) CT – computed tomography – 3D CT: What does the image represent? hyperdensity hypodensity isodensity

CT: What does the image represent? (X-ray) CT – computed tomography – 3D CT: What does the image represent? Image Feature Property Sample tissues Hypodensity (dark) Not much x-ray absorbed Air, fat, water, CSF Hyperdensity (bright) Lots of x-ray absorbed Bone, newly congealed blood Isodensity (gray) Some x-ray absorbed Gray matter, white matter

CT: What does the image represent? (X-ray) CT – computed tomography – 3D CT: What does the image represent?

CT: What does the image represent? (X-ray) CT – computed tomography – 3D CT: What does the image represent?

(X-ray) CT – computed tomography – 3D CT - Hemmorage

Realtime Imaging (Xray) Flouroscopy – 2D Xray advantage : Heart Blood Flow Surgery advantage : disadvantage: high radiation dose

(Xray) CONTRAST – Radiograph, CT, or Flouroscopy Barium Swallow Injection (Iodine Compound) Angiogram

(X-ray) CT – computed tomography – 3D

(X-ray) CT – computed tomography – 3D Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} 13um resolution mouse placenta vasculature mouse microCT/PET

Electromagnetic Spectrum PET – positron emission tomography Electromagnetic Spectrum

Inject Patient with Radioactive Drug PET – positron emission tomography Inject Patient with Radioactive Drug Late 1960’s Drug travels to metabolically active sites (many tumors have high metabolic activity) Drug emits (+) positrons (basically a positively charged electron) FDG - Fluorodeoxyglucose (most common drug) (F18 – + emitter – two hour half-life) Advantage functional imaging Disadvantage some ionizing radiation low resolution (4mm x 4mm x 4mm) need to make/buy FDG (cyclotron)

PET/CT - together CT PET (Xray) CT

PET – positron emission tomography β+ decay, positron travels several mm and collides with an electron produce a pair of annihilation photons (511kev, 180o) simultaneous detection 180o apart

PET – positron emission tomography Abnormal FDG collection Treated Tumor growing again on periphery

PET – positron emission tomography functional brain activity (mostly done with MRI now)

PET/CT - together

PET/CT - together CT PET PET/CT PET

microPET/CT– positron emission tomography Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} signal to noise good bad physics note: signal on expanding sphere drops as 1/R2 (surface area of sphere), therefore closer is better

Electromagnetic Spectrum Ultrasound Electromagnetic Spectrum Discovered (Norris) 1952, clinical 1962 Sound waves 1-15MHz (ear 20 – 20KHz) Echos (reflections) from different density interfaces are recorded Image soft tissue and blood flow (Doppler) Advantages: high resolution (mm) cheap real time imaging safe Disadvantages: skilled technician & interpretation small field of view (~20cm) bone and air problematic

Ultrasound Fetocopsy Image Example Typical ultra sound – sound reflections off surface Fetocopsy Image Example probe Arterial Blood Flow

Electromagnetic Spectrum MRI – Magnetic Resonance Imaging Electromagnetic Spectrum

MRI – Magnetic Resonance Imaging Mansfield and Lauterbur nobel prize 1978 first images 1st published MRI images of abdomen First brain MR Modern T2 image “Interesting images, but will never be as useful as CT” neuroradiologist, 1982 3 Tesla MRI Scanner

MRI Advantages Disadvantages safe expensive great soft tissue contrast long time many contrast options bad for bones mediocre resolution

3 Tesla Magnetic Field (60,000 times Earths field) MRI B0 B0

3 Tesla magnet field MRI Not all the protons line up – thermal energy Protons (hydrogen nuclei act like little magnets) B0 Collective Magnetic Moment of Protons

MRI Stage I Excite B0 Radio Waves end start Collective Magnetic Moment of Protons start end

MRI Stage II listen Make image based on Protons loosing energy Protons dephasing start Fat and water loose energy and dephase at different rates Slow Precession end Fast Precession T1 (energy lose time constant) Imaging T2 (dephasing time constant) Imaging Axial MRI Head Water Fat bright dark bright dark

CT versus MRI CT +Excellent bone imaging +Excellent new acute hemorrhage detection +Skull fracture, calcified lesion +Short scan time, metal devices allowed -Poor contrast and resolution -Radiation MRI +Excellent grey/white matter contrast & spatial resolution +Better for old hemorrhage (and new with Diffusion?) -Long scan time -Pts cannot have metal devices -Claustrophobia, obesity problems +No radiation - expensive

MRI: “Normal” Anatomy corpus callosum fornix thalamus midbrain pons medulla

MRI: “Normal” Anatomy superior frontal g. precuneus cingulate g. lingual g. g. rectus

MRI: Imaging deep structures (thalamus and basal ganglia) Caudate nucleus Putamen & globus pallidus

Disease MRI Tumor (can be combination of Edema and tumor tissue characteristics) Multiple Sclerosis – Active Lessions (basically edema – water)

Why MRI : Detection of Acute Stroke “Diffusion Weighted Imaging (DWI) has proven to be the most effective means of detecting early strokes” Lehigh Magnetic Imaging Center Conventional T2 WI DW-EPI (advanced technique) Sodium ion pumps fail, water goes in cells and can not diffuse.

MRI Brain Injury

MRI Excite Protons Wait then Listen to Protons MRA – magnetic resonance angiogram Single slice from MRA Excite Protons Wait then Listen to Protons

MRI Stack the slices to produce 3D image MRV (Veins) – reverse excite and listen slices MRA (arteries)

Angiography Refers to imaging of blood vessels Several types: conventional x-ray angiography Spiral / helical CT angiography magnetic resonance angiography

X-Ray Angiography inject pt. With contrast agent (e.g. sodium iodide) take series of images at intervals following injection (e.g. 1-second intervals) early images show arteries; later images show veins

Xray: Imaging Vasculature

Xray: Imaging Vasculature 1. Obtain scout 4. Take second image 5. Subtract second image from mask 2. Reverse image of scout = “mask” 3. Inject contrast

MR Angiography often don’t need contrast agent pulse sequences accentuate flowing tissues and minimize contrast from stationary ones usually both arteries and veins are shown together (but can be separated)

MR Angiography

r. Internal carotid injection Lateral view X-ray angiography

r. Internal carotid injection Lateral view X-ray angiography MCA and branches ACA and branches ophthalmic artery carotid siphon internal carotid

l. vertebral injection Lateral view X-ray angiography

Posterior inf. cerebellar artery l. vertebral injection Lateral view X-ray angiography PCA and branches basilar artery Posterior inf. cerebellar artery vertebral artery

Venous sinuses Lateral view X-ray angiography

Superior sagittal sinus Venous sinuses Lateral view X-ray angiography Superior sagittal sinus Superior sagittal sinus Great cerebral vein of Galen Straight sinus Confluence of sinuses Jugular vein & bulb

Anterior view MRA

Anterior view MRA ACA MCA MCA Internal carotid Carotid siphon Basilar artery

r. Internal carotid injection AP view X-ray angiography

r. Internal carotid injection AP view X-ray angiography ACA Carotid siphon MCA Internal carotid

l. Vertebral artery injection AP view X-ray angiography

l. Vertebral artery injection AP view X-ray angiography PCA vertebral artery

r. Internal carotid injection AP view X-ray angiography

Superior sagittal sinus r. Internal carotid injection AP view X-ray angiography Superior sagittal sinus Confluence of sinuses Transverse sinus Sigmoid sinus Jugular vein & bulb

Unused slides

Sound reflections Sound – density determines reflection like light (E&M) – index of refraction determines reflection for light (E&M) Sonar = 10 – 200KHz Incident Reflected Refracted (penetrated)

AMNIOCENTESIS-diagnostic / therapeutic C V S Ultrasound Doppler (frequency shift due to movement) Arterial blood flow Heart Valve functionality AMNIOCENTESIS-diagnostic / therapeutic C V S CORDOCENTESIS-sampling / transfusion BIOPSY- fetal skin / liver SHUNTS-vesicoamniotic / thoracoamniotic FETOSCOPY -usg guided FETAL GENE Rx- stem cell transplants