6Radionuclide and Hybrid Imaging

DR MUHAMMAD BIN ZULFIQARPGR III FCPS Services institute of Medical

Sciences/ Services Hospital LahoreGRAINGER & ALLISON’S DIAGNOSTIC RADIOLOGY

• FIGURE 6-1 PET-CT images from a patient ■with active lymphoma. The 18F-FDG uptake has been displayed in colour over grey-scale CT images in (A) transaxial, (B) coronal and (C) sagittal formats.

• FIGURE 6-2 Radionuclide images depicting ■three different cell types within the liver obtained using different radiopharmaceuticals. (A) 99mTc sulphur colloid taken up by Küpfer cells. (B) 99mTc HIDA taken up and excreted by hepatocytes. (C) Leucocytes labelled (ex vivo) using 99mTc HMPAO. (The crosses mark the costal margins.)

• FIGURE 6-3 Radionuclide images of breast cancer (arrows) ■demonstrating different uptake mechanisms in the same cell type (adenocarcinoma). Uptake of 18F-FDG on PET (A) is due to increased expression of glucose transporters and hexokinase. Uptake and retention of 99mTc methoxyisobutylisonitrile on gamma scintigraphy (B) are dependent on perfusion and expression of multidrug resistance p-glycoprotein. (Note uptake in nodal metastases in the axilla in case B, as indicated by the arrowhead.)

• FIGURE 6-4 Time–activity curves from the ■kidneys, bladder and aorta following intravenous injection of a radiopharmaceutical (99mTc MAG3) that is excreted by the kidney.

• FIGURE 6-5 CT (A, C) and PETCT ■ (B, D) images from a patient with right-sided non-small cell lung cancer (block arrow) shown in coronal (A, B) and transaxial (C, D) formats. A right hilar lymph node (arrow) is insufficiently enlarged to confidently diagnose nodal metastasis on CT but demonstrates uptake of 18F-FDG on PET, implying the presence of tumour cells.

• FIGURE 6-6 A fast-moving beta particle is ■deflected by a nucleus, producing a bremsstrahlung photon. (Redrawn from Hart G. Armes F 1992 Medical Physics for Advanced Level. Simon & Schuster Education, London.)

• FIGURE 6-7 (A) ■Photoelectric absorption, (B) Compton scattering. (Redrawn from Hart G. Armes F 1992 Medical Physics for Advanced Level. Simon & Schuster Education, London.)

• FIGURE 6-8 (A) A gamma ■camera. This model has two detectors mounted on the circular gantry ring to the left of the picture. SPECT studies are acquired by rotating these detectors around the patient. (B) Components of a modern ‘digital’ gamma camera with one analogue-to-digital converter (ADC) for each photomultiplier tube. (Image (A) courtesy of Siemens Medical Solutions.)

• FIGURE 6-9 99mTc spectrum and 20% ■energy window symmetrically placed around the primary emission at 140 keV. Note that some Compton scatter (dashed line) remains within the energy window around the photopeak.

• FIGURE 6-10 (A) ■Full width at half maximum is a measure of the width of a peak, taken at half its maximum height. (B) The effect of distance on resolution. Gamma rays from source B will pass through a larger number of holes in the collimator, and activate a larger area of crystal. Resolution is therefore poorer for the more distant source B.

• FIGURE 6-11 (A) Simple illustration of reconstruction by filtered ■back projection. The cancellation of back projection errors as the number of projection angles increases can be seen. This is achieved using a ramp filter applied to projections. (B) Schematic of iterative reconstruction: the reconstructed image is obtained by ensuring that estimated projections match the measured projections.

• FIGURE 6-12 A current generation dual-detector ■SPECT system (A) is much bulkier than the example of a system designed specifically for cardiac SPECT (D-SPECT: Spectrum Dynamics, Israel) (C). In the D-SPECT nine CZT detectors acquire during programmed rotation on their own axes so as to maximise counts from the cardiac region (D). The GE discovery NM570c uses similar CZT technology but is based on an array of fixed-position pinhole collimators (B).

• FIGURE 6-12 A current generation dual-detector ■SPECT system (A) is much bulkier than the example of a system designed specifically for cardiac SPECT (D-SPECT: Spectrum Dynamics, Israel) (C). In the D-SPECT nine CZT detectors acquire during programmed rotation on their own axes so as to maximise counts from the cardiac region (D). The GE discovery NM570c uses similar CZT technology but is based on an array of fixed-position pinhole collimators (B).

• FIGURE 6-13 (A) PET detects ■the two colinear gammas that are emitted when a positron annihilates with an electron. The two photons are detected in coincidence, permitting localisation of a line-of-response. The image of the activity distribution is determined normally via iterative reconstruction. (B) Most PET detectors utlilise a block design with multiple crystals connected to a small number of photomultiplier tubes.

• FIGURE 6-14 Myocardial perfusion images ■displayed in vertical long-axis format. The upper row (A) shows an artefactual reduction in uptake in the inferior wall (arrow) due to attenuation of gamma photons by the diaphragm. This artefact is removed by CT attenuation correction (lower row: B).

• FIGURE 6-15 PET-CT study in which the CT data (right) has ■been used for attenuation correction of the PET image (left). A crescent of lung just cranial to the left hemidiaphragm (arrow) demonstrates reduced activity—an artefact due to differences in the position of the left hemidiaphragm between acquisition of CT and PET data.

• FIGURE 6-16 Hybrid 3D SPECT-CT image ■showing uptake of 99mTc polyphosphate in the second metatarsal neck due to a stress fracture. The radioisotope uptake is displayed on a 3D reconstruction of CT images of the foot.

• FIGURE 6-17 Example of large gynaecological ■tumour, studied by simultaneous PET-MRI. Of note is the excellent registration demonstrating metabolic differences for different parts of the tumour. (Courtesy of Institute of Nuclear Medicine, University College Hospital, London.)

• FIGURE 6-18 Bone scintigram in a child with osteomyelitis of the left ■distal femur acquired using 99mTc methylene diphosphonate. The distribution of the radiopharmaceutical changes between the early tissue phase images (A, B) and the delayed images (C, D). The bones are visualised more clearly on later images. The epiphyseal plates show increased uptake, a normal finding in children. There are differences between the corresponding anterior and posterior projections and right–left (R–L) annotation on anterior and posterior images.

• FIGURE 6-19 SPECT-CT images in (A) ■transaxial, (B) coronal and (C) sagittal format following periareolar injection of 99mTc colloid into the right breast in a patient with breast cancer. Hybrid imaging shows the precise location of the sentinel node, which has accumulated the radiopharmaceutical.