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ENGG 167 MEDICAL IMAGING

Nov. 6

Nuclear Medicine & SPECT imaging

References: The Essential Physics of Medical Imaging, Bushberg et al, 2nd ed.Chapters 19, 21, 22, 24.

Physics and Radiobiology of Nuclear Medicine, G. B. Saha, 2nd ed. 2001.

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Schedule This Week

1) No class Wednesday

2) Journal club Thurs/Friday(choose a paper on MRI/PET/SPECT imaging)

3) Lab 5 can be due on Friday

4) No lab this week!

5) Scan through Chapters 19, 21& 24 in Bushberg

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Nuclear Medicine

Ref: Bushberg

1) Gamma Camera & SPECT imaging2) Radionuclides3) Dose Assessment

No lab this week!Scan through Chapters 19, 21& 24 in Bushberg

3rd Journal Club Review – Thursday/Friday(see last slide today for instructions)

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Nuclear Imaging with a Gamma Camera

Radioactive atom held within a pharmaceutical molecule, allowing specific localization and imaging

Often used to search for bone metastases of cancer tumors

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Nuclear Imaging with a Gamma Camera - example 1

Reference: http://www.med.harvard.edu/JPNM/TF99_00/Sept21/WriteUp.html

PresentationA 65 year old male with a history of non-insulin dependent diabetesmellitus, alcohol abuse, and severe peripheral vascular diseasepresented with a non-healing ulcer of the left first toe.

Three Phase Bone Scan25 millicuries of Tc-99m MDP were administered intravenously. Dynamic 2-5 second images were obtained for 60 seconds after injection (angiographic phase). A static tissue phase image was obtained. Delayed skeletal phase images were obtained at 2-4 hours after injection. Gallium Scan5 milliCuries of Ga- 67 citrate were administered intravenously. Delayed images of the feet were obtained at 48 hours.

Imaging FindingsRadiography, three phase bone scan and gallium scan were performed.

Three Phase Bone ScanThe flow phase of the three-phase bone scan demonstrates diffuse increased flow to the left foot with focal accumulation in the first digit. On the tissue phase, there is marked asymmetry with increase activity in the left foot. In addition, there is mild localization in the first digit (shown by arrow). The delayed images demonstrate focal uptake at the left first MTP joint and first interphalangeal joint (shown by arrows). The uptake in three phase bone scans is related to blood flow and osteoblastic activity. In the study by R.H. Gold et al, the mean sensitivity is 85% and the specificity is 54% (3). Gallium ScanThe gallium scan (bottom two images) demonstrates focal increased tracer uptake in the left first toe.Mechanisms of Ga-67 citrate uptake include: (1) direct leukocyte and bacterial uptake, (2) lactoferrin and transferring binding, (3) increased vascularity, and (4) increased bone turnover.

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Single photon emission computed tomography (SPECT) with gamma cameras

Ref: Bushberg

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Gamma camera design – scintillators with PMTs

Ref: Bushberg

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Localizing the signal X, Y, Z

Ref: Bushberg

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Nuclear Medicine Radionuclides

Ref: Bushberg

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Tc99m - most common radionuclide used

Ref: Bushberg

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SPECT images – detection of counts

Ref: Bushberg

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Gamma camera – has limitation of resolution versus distance

Ref: Bushberg

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Gamma camera imaging system performance

Ref: Bushberg

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camera images – correction for sparse sampling

Ref: Bushberg

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emission images – homogeneous test fields

Ref: Bushberg

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Multiple sequential projections for SPECT imaging

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Filtered Backprojection SPECT imaging

Ref: Bushberg

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Attenuation correction in computed SPECT imaging

Ref: Bushberg

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Imaging the temporal sequence of radiation can be essential for useful information about function.

Ref: Bushberg

Time-activity curve

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Sequenced imaging - heart imaging

Ref: Bushberg

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Sequenced imaging - heart imaging

Ref: Bushberg

Tc99m labeled red blood cells

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Thyroid Scan - single element gamma camera

Ref: Bushberg

• Safety monitoring for those who handle I-123 or I-131.• swallow capsule of weakly activated NaI• measure uptake in thyroid, compare values to that of a phantom and subjects thigh.• this activity provides a reference, and higher values than normal indicate occupational exposure has occurred.

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Nuclear Fission Reactor production of 99Mo

Ref: Bushberg

Fission products are generated from rods of 235U inserted into reactor core.

Chemical separation of 99Mo, 131I, 133Xe is readily possible from rod material.

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Nuclear Fission Reactors are also used to generate isotopes via neutron capture

Ref: Bushberg

Low specific activity due to problems separating target materialfrom product, but can readily produce:

One exception which has high separation yield is 125I

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Radionuclide generators: separate long decay parent from fast decay daughter nuclide

Ref: Bushberg

99Mo from 99mTc

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Radionuclide generators: separate long decay parent from fast decay daughter nuclide

Ref: Bushberg

Typically delivered with 37 to 111 GBq activity (1 to 3 Cu)Mo decay allows the generator to be “milked” every dayTc buildup occurs between milkingsGenerator last about 1 week

Tc-99m radiopharmaceutical prepared by injection of 99mTcO4 into a sterile vial of freeze-dried pharmaceutical.

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Medical Radionuclide Uses - I

Ref: Bushberg

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Medical Radionuclide Uses - II

Ref: Bushberg

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Shielding calculations

Ref: Bushberg

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Exposure Rate Constants

Ref: Bushberg