The limitations of several imaging methods led to hybrid imaging. In nuclear medicine, radiotracers cause physiological processes that impair the accurate identification of anatomic structures. Simply put, some modalities can indicate metabolic changes but not structural alterations.
Hybrid photos can be seen independently or merged. A dual-head scintillation camera and low-power X-ray tube became the first hybrid imaging system. Fusion imaging technologies have enhanced diagnostic, staging, and treatment planning. Hybrid imaging combines functional and anatomical picture generation.
CT and MRI can image structural anatomy well. However, such imaging techniques may not provide a full picture. In cancer patients, anatomical imaging modalities alone cannot diagnose, stage, or track treatment response. This is because, early in such disorders, functional alterations may occur without physical abnormalities. Some imaging techniques provide good functional changes but poor anatomical details.
The aforesaid factors led to the development of a technology that combines two imaging modalities to compensate for their weaknesses. Fusion imaging, hybrid imaging, anato-metabolic imaging, co-registration, etc. resulted.
HYBRID IMAGES
Hybrid imaging involves combining two imaging modalities—usually an anatomical and a functional modality—to reach a desired outcome. Different modalities are blended depending on the intended result and the restrictions of the modality that has to be complimented.
Current hybrid imaging includes: ultrasonography/MRI, which permits, ultrasound-guided MRI biopsies. Single photon emission computed tomography (CT), Fuses SPECT functional nuclear medicine pictures with CT anatomical data.
Photon emission tomography (PET) is the major hybrid imaging technique discussed here.
PET and MRI are accessible, although not commercially.
PET/CT is the fastest-growing hybrid imaging technique; therefore, educating staff to manage its developing diversities is important.
PET scan basics
PET is positron emission tomography. Nuclear medicine imaging employs radiotracers or radiopharmaceuticals to study normal and abnormal bodily activity. Radiotracers are radioactive molecules. The radioactively tagged molecule is generally one that the body employs in metabolism or has properties that make it acceptable. Fluoro-deoxy-glucose, which replaces one or more glucose atoms with F-18 fluorine, is a frequent nuclear medicine radiotracer. The body utilizes glucose for energy, and active cells and tissues consume more glucose.
Thus, radioactive tracers employ metabolic activity differences between normal and diseased tissues. Hypermetabolic tissues acquire more radioactive traces. PET scans usually show increased metabolism in the abnormal tissue. Due to cancer's elevated metabolic rate, it's used in many health conditions, including cancer. Heart and brain disorders have other uses.
Pet gear
The PET machine detects and measures radiopharmaceutical radiation in the organ of interest, since PET scans employ radiopharmaceuticals to analyze metabolic activities. PET scanning employs a computer and a photon-detecting camera. The camera and computer produce metabolic activity images. Gamma camera data produces computer pictures.
Pet scan's working principle
Radiotracers, when delivered into the body, produce radiation depending on their concentration in a tissue or organ. The detectors then use this radiation to create pictures of the body. Radiotracers are frequently injected. PET scans employ radioactive radiotracers.
18F-fluoro-2-deoxy-glucose, labeled with radioactive fluorine, is the most frequent radiotracer. Radiotracers produce photons that a specialized camera detects and sends to a computer for viewing. PET scans use tissue metabolic activity to diagnose biochemical conditions. In malignant tissues, increasing activity increases radiotracer absorption and concentration. Thus, malignant growths would look brighter than surrounding tissues due to increased radionuclide concentrations in aberrant tissue due to increased chemical activity or metabolic rate, such as cell division. "Hot spots" represent cancerous regions in the picture, whereas "cold spots" are normal tissues. So tissue brightness indicates activity.
PET scan limitations
In various illnesses, PET scans are limited, as illustrated below:
Size of the tumor: if a tumor is very small (less than 7mm), its metabolic rate may not increase significantly enough to cause any remarkable increase in the uptake of the radiotracer, and eventually there will not be an appreciable change or difference to be noted on the tissue in the image, thus a small, less active tumor will be missed. The main issue is that PET scan cameras' spatial resolution causes false-negative readings in extremely tiny cancers or microscopic tumor deposits.
Slow-growing tumors, such as carcinoid masses, adenomas, and some carcinomas, may not absorb enough tracers to distinguish them from normal tissue, resulting in false-negative results.
Blood sugar level: If blood sugar is too high, tissues will absorb more normal blood glucose and less radiotracer. At least 4 hours before a PET scan is important for patient preparation. Lowers blood sugar. Diabetics also have worse PET scan accuracy.
PET scans can produce false negatives for tiny, low-activity malignancies or false positives for diabetes, among other causes.
CT SCAN
CT scans employ X-rays to scan the body from multiple angles. These photos from diverse angles are computer-processed to provide cross-sectional views of the body or region of interest. CT scans employ radiographic radiation. CT scans provide more information than traditional radiography because they can acquire 3D pictures of the body, while conventional radiography generates 2D images by superimposing structures.
CT scan machines are spherical with holes in the middle. The patient lies on a motorized table that glides in and out of the hole like a tunnel.
Straps keep the patient in place after placement to avoid motion blur during the test.
The gantry, the machine's most visible portion, is rounded. X-ray tubes and detectors are within. The X-ray tube rotates around the patient while the motorized tables slowly move them in and out of the hole. Detectors record X-rays transmitted at various angles and places around the region of interest. The computer creates bodily pictures from this data.
CT Workflow
Computerized tomography works by transmitting X-rays through the body, detecting them with detectors, and using the computer to measure the attenuation coefficient of the tissues the radiation passed through to reconstruct images.
CT scan limitations
CT scans provide volumetric information in diverse situations for 3-D imaging. It's detailed spatially. It cannot give extensive information on bodily functionality or organ metabolism. If there is no morphological or anatomical alteration, it may not be possible to identify some disorders early on. When tissue is aberrant, metabolic or biochemical abnormalities occur before morphological or anatomical changes. CT scans cannot identify defects; hence, they are false negatives.
Lung cancer case study
Lung cancer and other malignancies are staged differently. TNM staging is currently the norm for lung cancer.
Tumor-Node-Metastasis (TNM). These three staging factors
main tumor (T) location and severity
Intrapulmonary, hilar, and mediastinal lymph node changes
Other pulmonary conditions and metastases
We can place a patient in any of the four phases (I–V) based on these three factors. This rating or grading distinguishes patients who can be cured from those who need palliative care.
PET/CT procedure
A PET/CT picture may be understood by comparing it to a CT scan of the same body part. The patient does not move between scans. Thus, CT scans will connect metabolic abnormalities to anatomy.
The CT scanner transmits X-rays through various places in the region of interest and reconstructs 3-D pictures. The PET scan uses radiotracers to identify biochemically active regions based on radiotracer concentration. These two scans create pictures with anatomical and functional information. Note that PET and CT scans are taken consecutively. The motorized table allows the PET and CT to progressively collect pictures from a body spot.
In conclusion, Hybrid imaging helps radiologists diagnose and treat. This aids in cancer detection and staging. Cancer begins with cell metabolic and chemical alterations. It changes mitotic cell divisions, causing excessive cell growth. Organ size changes eventually. Later, malignant growths fragment and target surrounding and distant tissues and organs.
Thus, metabolic and structural alterations must be examined in malignant growths. Metabolic alterations occur before structural changes, according to research.
Hybrid imaging takes advantage of the synergy between two imaging modalities to maximize their strengths. Each also balances the other's deficiencies.
CT and PET scans are excellent cancer diagnostics. Even alone, they convey vital cancer information. These modalities are beneficial even when used alone, although they have limits. CT shows cancer anatomy but not metabolic alterations. CT is almost useless in the early stages of such malignancy, when anatomical alterations may not be seen. PET shows early metabolic alterations but not anatomical features.
As seen above, combining CT and PET into a single modality has greatly improved cancer detection and treatment efficiency.
Hybrid imaging includes PET and CT. It is the most sophisticated hybrid imaging modality. This seminar's major emphasis, lung cancer, is diagnosed and staged using it.
Before PET/CT was developed, CT and PET scans were done separately and reviewed simultaneously. Since the exams were done separately, the patient's posture is rarely the same. Since the two scanners are "fused" and the two scans are done without the patient changing position, PET/CT as a hybrid has this benefit. This improves PET/CT hybrid accuracy. It's also wonderful to know that PET/CT is being improved to be more efficient, accurate, and cost-effective.
References
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“Imaging Evolution: Hybrid PET/CT Scans.” Imaging Technology News, 3 May 2012, www.itnonline.com/article/imaging-evolution-hybrid-petct-scans.
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