BMME 560 & BME 590IMedical Imaging: X-ray, CT, and

Nuclear Methods

Nuclear Medicine Imaging Part 2

Today

• Clinical and research applications– Planar scintigraphy– Cardiac imaging– Cancer imaging– Neurological imaging– Other

Planar Scintigraphy

• Basically, this is SPECT without the CT part.

• Take one or two views of the emission data and base the diagnosis on that

• Like projection radiography vs. X-ray CT

• For focal areas, use pinhole

Thyroid Scan

• A common procedure is to study the function of the thyroid gland

• Use a pinhole collimator to get magnification and focus on the organ.

Isotope Half-life Energy123I 13 hours 159 keV

131I 8 days 356 keV

99mTcO4 (pertechnetate)

6 hours 140 keV

High-energy, betas

Expensive, 4-24 hours distribution

Less efficient uptake, cheap, 15-30 min distn

Thyroid Scan

Studies regional function of thyroid via its uptakeHyperthyroidism, hypothyroidism, benign masses vs. cancers

Cold nodule

Source: http://www.uhrad.com/spectarc/nucs022.htm

Bone Scan

• 99mTc-MDP is incorporated into extracellular matrix as new bone is formed

• Uptake depends on local blood flow and osteoblast activity

• Used to examine cancer metastasis to bones• Also, stress fractures and other bone functional

abnormalities• Also, functional abnormalities when other

tissues act like bone

Bone Scans

Metastatic involvement

Source: http://www.mcg.edu/radscape/CaseStudies/Christy_Barnosky/MetStats.htm

Bone Scans

Calcified uterine fibroids above the bladderSource: http://www.uhrad.com/spectarc/nucs020.htm

Stress fracture of the footSource: http://www.uhrad.com/spectarc/nucs012.htm

SPECT Bone Scan

• Reference: http://www.uhrad.com/spectarc/nucs010.htm

Cardiac Functional Imaging

• All major imaging modalities are working on the heart– CT: Fast multislice cardiac CT– Cardiac MRI– Echocardiography– SPECT: Cardiac perfusion imaging– PET: Cardiac viability and perfusion

Cardiac Perfusion Imaging

• Measurement of blood flow to cardiac tissue via coronary arteries

• Coronary arteries may be blocked by plaques

• Stress versus rest studies may reveal a difference

• SPECT is cheap and has long been used for this purpose– Several agents, mostly 201Tl (older) and 99mTc

SPECT Cardiac Imaging

The left ventricle takes most of the blood flow to the heart.

It is shaped like a rounded cone.

Dark regions indicate reduced blood flow to a portion of the myocardium

SPECT Cardiac Imaging

• But, reduced blood flow could have more than one reason:– The coronary artery supplying it is partially

blocked– The tissue is dead

• Which is worse?

• To determine, try imaging at stress and rest

Cardiac Imaging

• If the coronary artery is blocked, the physician must make a treatment decision:– Revascularize (coronary bypass)– Pharmaceuticals

• This depends on the assessment of the outcome of each procedure– If an expensive procedure (bypass) will help, do it.– Otherwise, don’t

• Depends on viability: Could the cardiac tissue be restored?

PET Cardiac Imaging

• FDG is a glucose analog; stunned cardiac tissue still uses some glucose.

• FDG helps determine the viability of tissue: could it be brought back?

• 13NH3 and rubidium are PET perfusion agents

Cardiac PET

13N FDG

10 min half-life!

Can also use 82Rb – 6-hour half-life and generator-produced

Would you send to bypass?

Source: http://www.thompsonpet.com/zportal/portals/phys/clinical/jnmpetlit/index_html/JNM_CardApps

Gated Imaging

• Each event recorded by the detector has a time associated with it.

• By synchronizing these times with the ECG signal, we can divide the events into different pars of the cardiac cycle

• A 3D movie of SPECT or PET

• Assess wall motion as well as perfusion

• What price do we pay?

Gated Imaging

Conventional SPECT

Gated SPECT

Sixteen 3D datasetsor one 4D dataset

One 3Ddataset

Gated SPECT

Cancer Imaging

• Cancers may be anatomically similar to the surrounding tissue, but functionally different.

• Active cancers take up lots of glucose– So do inflammations

• PET’s first approved clinical application was in the study of lung cancer

• SPECT is used to image cancers as well

PET Cancer Imaging

• Pre- and post-therapy images of lung cancer and metastases

Source: Appl Radiol 31(6):9-17, 2002. © 2002 Anderson Publishing, Ltd.

PET Cancer Imaging

Source: http://www.bocaradiology.com/Procedures/PET.html

Liver, but no metsDiffuse spread of prostate cancer to bone

PET Cancer Imaging

• Whole-body PET is currently approved for:– Non-small-cell lung carcinoma– Head and neck carcinoma– Lymphoma– Melanoma– Colorectal carcinoma– Esophageal carcinoma– Thyroid carcinoma– Solitary pulmonary nodule (lung)

SPECT Cancer Imaging

• 111In-Prostascint SPECT/CT– Binds to Prostate-specific membrane antigen– FDG PET is not very good for this purpose –

Why?

Source: http://ieeexplore.ieee.org/iel5/9892/31436/01462741.pdf?arnumber=1462741

Neurological Imaging

• The brain is important, too.

• Applications include regional cerebral blood flow (SPECT) and brain activation studies (PET)

Brain SPECT

• 99mTc-HMPAO and 99mTc-ECD are brain perfusion agents– Cross blood-brain barrier and are then trapped– Highest signal from gray matter– 123I-IMP behaves similarly

• Some development of neuroreceptor ligands– For imaging of dementia and other neurological

disorders

Reference: http://brighamrad.harvard.edu/education/online/BrainSPECT/BrSPECT.html

Brain SPECT

Ischemic stroke via 99mTc-HMPAO

Source: http://brighamrad.harvard.edu/education/online/BrainSPECT/Contents.html

Physicians look for asymmetry

PET Neuroimaging

• Can use FDG

• Interesting things can be done with other radionuclides– 11C (20 minutes) is used to label all kinds of

organic molecules– 15O (2 minutes) is incorporated into water

Source: http://clinicalcenter.nih.gov/pet/images.html

FDG Brain PET

Shows brain metabolic activity

Gray matter is hot

This patient is normal. What would a dark region indicate?

11C Raclopride

This is a dopamine receptor antagonist.

The basal ganglia light up.

15O-water

Shows cerebral blood flow, but a little different from SPECT ligands

Shows tissue function with respect to water transport – does not get trapped in tissue

Noisy

2 minute half-life!

PET Neuroimaging

Abnormally low activity in right temporal lobe in epileptic patient

Source: http://www.bocaradiology.com/Procedures/PET.html

FDG and C-11

FDG

C-11 methionine

Patient imaged post-radiation therapy for brain tumor. FDG shows suspicious region, but C-11 is more specific

Source: http://www.med.harvard.edu/JPNM/TF00_01/Sept26/WriteUp.html

White blood cell SPECT

• Tried-and-true method: Extract patient’s blood sample, isolate leukocytes, label with 111In, and reinject– Can also use 99mTc

• Newer method: “in vivo labeling” of leukocytes with 99mTc LeukoScan™

• Leukocytes collect at sites of infection and inflammation– Used in all parts of the body

111In WBC SPECT

Source: http://www.rad.kumc.edu/nucmed/clinical/wbcscan.htm

67Ga-citrate

• Gallium was one of the earliest NM agents

• It binds to a protein (transferrin) in the circulating blood and follows it to sites of infection

• Problems with gallium– Messy – 3 energy peaks (93, 185, 300 keV)– Long-lived – 78 hour half-life

Ga-67 vs. In-111

Patient has pneumonia – Ga-67 is better for opportunistic infections

Source: Journal of Nuclear Medicine Technology Volume 32, Number 2, 2004 47-57

SPECT Aerosol Agents

• 133Xe and 99mTc-Technegas are delivered through inhalation

• Lung ventilation is assessed by gating to respiratory cycle

• Often compared with lung perfusion via 99mTc-MAA

Source: radchem.nevada.edu/chem312/lectures/chem%20312%20lect%204%20radiotracer.ppt

New Things

• Radiolabeled antibodies

• Reporter genes– Via NaI symporter (NIS) molecule

• NIS gene product mediates radioiodine (PET, SPECT) transport into the cell

• NIS has been sequenced

• Faster, cheaper labeling methods