Basics of thoracic nuclear medicine

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Nuclear medicine, or nuclear scintigraphy, is a branch of medical imaging that uses radiopharmaceuticals (pharmaceuticals labelled to radioactive atoms) to evaluate physiological processes and diagnose a variety of diseases. Nuclear medicine differs from other imaging modalities in that it shows primarily the function of the system being investigated, as opposed to its anatomy. The chapter focuses on Indications; Restraint and patient preparation; Technique.

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Image of 5.1
5.1 TAC from the CrVC in a normal dog illustrating a good bolus injection. The curve was obtained by drawing a ROI over the CrVC and plotting the counts in the ROI (y axis) over time in seconds (x axis). Notice the tall and narrow-based peak of the curve. The width of the peak at 50% of the peak maximum height (full width half maximum, FWHM) is 1 second, indicating an excellent bolus.
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5.2 Left lateral images illustrating a normal first pass radionuclide angiogram in a dog. The images are taken at a rate of 4 frames per second, representing the 3 seconds immediately after the intravenous injection of Tc DTPA. The radionuclide outlines the CrVC, (top left), right heart, lungs, left heart and aorta. Notice that the margins of the aorta are distinct and the lung field clears completely (last two images, bottom right) during the levophase.
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5.3 TAC from the CrVC in a normal dog illustrating a split bolus. This is an example of a biphasic bolus: the first peak in the TAC (A) is followed by a second peak (B), which may be erroneously interpreted as a recirculation peak compatible with a left-to-right shunt. This mistake is easily avoided by evaluating the TAC in conjunction with the dynamic acquisition.
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5.4 Pulmonary TAC (blue) in a normal dog showing an initial increase and successive sharp fall of the pulmonary counts as the radioactive bolus passes through the pulmonary circulation (QP). The curve in red represents systemic activity in the lungs (QS), which is due to blood flow in the bronchial branches of the broncho-oesophageal artery. The dotted lines represent fitted curves, which were generated by the computer during the analysis and calculation of QP:QS ratio. The image in the top right corner illustrates positioning of the pulmonary ROI in the caudodorsal aspect of the lungs.
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5.5 Pulmonary TAC in a dog with a left-to-right shunt. The curve was generated in the same way as the one in Figure 5.4 . Notice the large systemic peak (QS), indicating recirculation of the radiopharmaceutical through the left-to-right shunt.
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5.6 TAC in a dog with a left-to-right shunt, showing the reference points necessary for calculation of the C2:C1 ratio. C1 is the point of maximum pulmonary counts; Tmax is the time after the beginning of the pulmonary upslope at which C1 occurs; C2 is the point on the curve at 2xTmax. The C2:C1 ratio in normal dogs should be <0.5.
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5.7 Pulmonary perfusion study in a dog presented for evaluation of possible PTE. Note the small but intense focus of activity in the apex of the right cranial lung lobe (arrowed). This was a Tc-MAA clot.
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5.8 Left lateral view of the lungs of a normal dog after intravenous injection of approximately 37 MBq of Tc-MAA. Notice the uniform radiopharmaceutical distribution within the lungs, with no evidence of distribution outside the pulmonary capillaries. The smooth photopenic area seen cranioventrally represents the cardiac notch.
Image of 5.9
5.9 Mucociliary scan in a normal dog. The two static foci of radioactivity to the right of each image represent external markers positioned at the caudal border of the scapula and 20 cm cranial to it. The images are dorsal views obtained at 0, 5, 10, 15, 20, 25, 30 and 40 minutes after deposition of a small droplet of Tc-MAA just cranial to the carina. The radioactive droplet is at the level of the caudal external marker at 0 minutes (top left image); subsequently, the droplet moves cranially and is almost at the level of the cranial marker at 40 minutes (bottom right image).
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