Nuclear Imaging Nuclear medicine is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear medicine scans are usually conducted by Radiographers. Nuclear medicine, in a sense, is Radiology done inside out" or "endoradiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-Rays. Nuclear imaging uses low doses of radioactive substances linked to compounds used by the body's cells or compounds that attach to tumor cells. Using special detection equipment, the radioactive substances can be traced in the body to see where and when they concentrate. Two major instruments of nuclear imaging used for cancer imaging are PET and SPECT scanners.

PET Scan The Positron Emission Tomography (PET) scan creates computerized images of chemical changes, such as sugar metabolism, that take place in tissue. Typically, the patient is given an injection of a substance that consists of a combination of a sugar and a small amount of radioactively labeled sugar. The radioactive sugar can help in locating a tumor, because cancer cells take up or absorb sugar more avidly than other tissues in the body. After receiving the radioactive sugar, the patient lies still for about 60 minutes while the radioactively labeled sugar circulates throughout the body. If a tumor is present, the radioactive sugar will accumulate in the tumor. The patient then lies on a table, which gradually moves through the PET scanner 6 to 7 times during a minute period. The PET scanner is used to detect the distribution of the sugar in the tumor and in the body. By the combined matching of a CT scan with PET images, there is an improved capacity to discriminate normal from abnormal tissues. A computer translates this information into the images that are interpreted by a radiologist. PET scans may play a role in determining whether a mass is cancerous. However, PET scans are more accurate in detecting larger and more aggressive tumors than they are in locating tumors that are smaller than 8 mm and/or less aggressive. They may also detect cancer when other imaging techniques show normal results. PET scans may be helpful in evaluating and staging recurrent disease (cancer that has come back). PET scans are beginning to be used to check if a treatment is working - if a tumor cells are dying and thus using less sugar.

SPECT Scan Similar to PET, Single Photon Emission Computed Tomography (SPECT) uses radioactive tracers and a scanner to record data that a computer constructs into two- or three-dimensional images. A small amount of a radioactive drug is injected into a vein and a scanner is used to make detailed images of areas inside the body where the radioactive material is taken up by the cells. SPECT can give information about blood flow to tissues and chemical reactions (metabolism) in the body. In this procedure, antibodies (proteins that recognize and stick to tumor cells) can be linked to a radioactive substance. If a tumor is present, the antibodies will stick to it. Then a SPECT scan can be done to detect the radioactive substance and reveal where the tumor is located.

Transaxial slice of the human brain (top) acquired with different imaging modalities (bottom) from left to right: X- ray CT, MRI, SPECT and PET

As an example of similar results with PET/CT and MRI, the images are of a 56-year- old patient with glioblastoma multiforme on the right side in the frontal area close to interhemispheric fissure. Top: PET/CT data show low-dose, noncontrast-enhanced CT scan (left), corresponding fusion image (center), and C-11 methionine PET image (right). Bottom: PET/MRI data show T2-weighted FLAIR image (left), fusion image (center), and PET image (right).

PET/MR images of a 60-year-old patient with anaplastic astrocytoma with right parafalxial tumor extension. MRI and PET datasets were simultaneously acquired at coronal (cor), sagittal (sag), and transverse (tra) sections.

These images demonstrate the fusion of metabolic function technology and morphology imaging technology. The coronal CT image (left) and the coronal PET image (middle) is fused into a PET/CT image (right). Hybrid PET/CT improves the sensitivity and specificity of FDG-PET imaging.

PET/CT images can be made in multiple planes. The sagittal images are shown above. This type of technology allows the radiologist and oncologist to monitor treatments verified by osteoblastic and osteolytic changes. Sequential studies on the same patients are not contributing important data about the nature of breast cancer bone metastasis, treatment, and prognosis with current methods of patient strategies.

Sixty-five-year-old female with a history of thyroid and metastatic breast cancers as well as schwannoma which was surgically resected. On restaging PET/CT: MIP, transaxial PET, CT, and fused images (A) demonstrated an unsuspected finding of recurrent schwannoma in addition to metastatic breast cancer. PET/CT finding was confirmed on MRI (B). The patient subsequently underwent surgical resection of the recurrent shwannoma.

Eighty-year-old female with non-small-cell lung cancer in the right lung status post Cyber knife therapy. On restaging PET/CT: MIP (maximum intensity projection) and transaxial PET, CT, and fused images (A) demonstrated complete response to therapy in the right lung and a new left temporoparietal lobe lesion suspicious for metastasis. PET/CT finding was confirmed on MRI (B). Adding the brain to the imaged field of view changed both staging (I–IV) and management as patient underwent whole brain radiation

Seventy-year-old male with bronchogenic carcinoma in the right lung. On initial staging PET/CT: MIP, transaxial PET, CT, and fused images (A) demonstrated a single lesion in the right lung and unsuspected photopenia in the left frontoparietal lobe that corresponds to a hypodensity on CT suspicious for metastasis. PET/CT finding was confirmed on MRI (B). Adding the brain to the imaged field of view changed both staging (I–IV) and management as patient underwent whole brain radiation.

Seventy-one-year-old male with metastatic squamous cell carcinoma of the head and neck. On follow-up PET/CT: MIP, transaxial PET, CT, and fused images (A) demonstrated an unsuspected hypermetabolic focus is the right frontal lobe with no definite abnormality on CT in addition to metastatic head and neck cancer. Brain MRI was negative for metastasis (B). In this case PET was falsely positive and the focal uptake in the right frontal lobe was thought to be due to artifact

Computed tomographic perfusion acetazolamide study, left hemisphere findings. The bottom row left image and fourth image over represent cerebral blood flow before (left arrow) and after acetazolamide (right arrow). Note improvement in cerebral blood flow after administration of acetazolamide (right arrow). This finding is consistent with the presence of vascular reserve and thus, revascularization is not indicated.

CT (top) and 99m Tc-HMPAO SPECT (bottom) images from 16-y-old patient with traumatic brain injury after traffic accident. (A) CT at time of admission shows subarachnoid hemorrhage with small contusional hemorrhagic foci in both frontal lobes (orange arrowheads). Glasgow score was 12. During hospitalization, patient’s clinical status worsened, and Glasgow score decreased to 6. No changes were seen on CT scan. SPECT was subsequently performed and shows absence of tracer uptake (cold areas) in anteromedial aspect of both frontal lobes corresponding to hemorrhagic lesions, in addition to global hypoperfusion, more marked in both frontal cortices (white arrows). (B) CT and SPECT images obtained 1 mo later at time of discharge after clinical recovery. Hypodense images in both frontal lobes can be seen on CT as consequence of hematoma’s resolution. Corresponding cold areas persist on SPECT image (orange arrowheads) but show improvement in global cerebral perfusion, particularly in both frontal lobes (white arrows).

CT and SPECT perfusion imaging of a patient with left frontal primarily brain trauma. In the hemorrhagic lesion seen on the CT in the right posterior temporal region, SPECT images show an absence of perfusion.

Pattern of cerebellar perfusion on single photon emission computed tomography in subcortical hematoma: A clinical and computed tomography correlation.

Neuroimaging findings of the patient. Fluid-attenuated inversion recovery oblique coronal brain magnetic resonance imaging shows left hippocampal sclerosis (A). Increased blood flow during a complex partial seizure is seen in the left temporal region on 99m Tc- ethylcysteinate dimer single photon emission computed tomography (B). 18 F- fluorodeoxyglucose positron emission tomography during forced thinking (C), and its statistical parametric mapping (D) shows focal hyper metabolism in the left mesial temporal region and the right cerebellum.

This composite shows the different imaging planes for CT that can be correlated with SPECT images. The SPECT images are superimposed on the CT slice giving precise anatomical reference for functional data.