1. Advantages:
Reduce the scan time: The system can be simultaneously acquired MR signals pet scanning process, the scan time can be greatly shortened. The new body PET / MRI scanning can be completed within a comprehensive systemic 30min, get all the MR and PET larva. Conventional MR and PET were examined, at least an hour or longer.
Accurate positioning: To achieve consistent anatomical spatial information, PET / MRI in the same frame of reference standards, access to MR and PET data simultaneously in a single scan, the possibility of secondary scan positioning error caused by the absence, for small, the great value of early diagnosis of disease .
Eliminate motion artifacts: PET / MRI gated MR technology to freeze motion artifacts, obtain high-quality images (eg heart) imaging is critical to have a physiological organ movement.
Physiological Synchronization: By simultaneously scanning, PET / MRI can realize Metro metabolic and physiological functions synchronized on MR and PET helps accurate diagnosis of the disease.
2. The potential clinical value: comprehensive synchronization through early diagnosis the possibility of obtaining personal structure, function and metabolic activity of information, PET / MRI greatly improve the early diagnosis of disease, may be a tumor, location, nature, monitoring work imaging support. Compared with PET / CT, PET / MRI has an unparalleled advantage in brain tumors, bone tumors, urinary tract tumors, liver and other abdominal tumor diagnosis, analysis, efficacy, etc., for the diagnosis of lung lesions is a little less in PET / CT.
3. Application of the nervous system: Advances in degenerative diseases, through the receptors, amyloid deposition shows that efforts to diagnose and identify aspects of Parkinson's, Alzheimer's disease early can use PET / MRI perfect interpretation . It is expected that, PET / MRI opens understand many neurological disorders such as Alzheimer's disease, epilepsy, depression door pathology and progress of the disease. PET is now able to identify mild cognitive impairment and early diagnosis of Alzheimer's disease, but still reduce the amount of brain volume caused by atrophy of the brain can not be measured, but the PET and MR joint, the more accurate clinical evaluation of the patient in the same patient cognitive impairment and brain atrophy case situation. PET / MRI of brain tissue also looking to restore hope to stroke patients. In the study of stem cell therapy, PET / MR can simultaneously obtain anatomical, functional and biochemical information about the body's tissues and cells, displayed in cell migration to damaged brain cells trajectory, more long-term observation to whether stem cell survival, as well as the identification of stem cells is how to integrate into the body's neural network could speed research from the laboratory to clinical application to promote the development of stem cells.
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1.PET/MR current problems
pet photomultiplier tubes barrier magnetic interference
Can MR attenuation correction for PET image problem
PET / MR examination was longer than PET / CT
PET / MR by an expensive, a PET / CT several times
PET / MR weight greater than PET / CT, the higher the requirements of the site
2. The end of November 2006, Krroxvivle Tennessee Medical Center's Siemens PET / MR image fusion performed the world's first PET / MR synchronous acquisition, the results are encouraging. PET / MRI applications in brain tumor diagnosis results show that for the brain tumor lesions diagnostic detection rate has improved significantly. Conducted with PET / MR pediatric epilepsy research lesion localization, the results show an increase accurate diagnosis than other methods.
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1 was analyzed in terms of imaging agent, PET / CT apparatus itself and the human body and the like. The following major developer and analyze the impact on the human body PET / CT examination results.
2.1 Effect imaging agent
18F so as to exchange with hydroxyl groups and the binding of calcium hydroxyapatite crystals, suitable for whole body bone scan. Clinically 18F ion is the most sensitive diagnostic pharmaceutical body bone metastasis, but also many benign lesions of bone uptake of 18F height, should pay attention to the differential diagnosis. Further imaging agents also affect the ability to display results of the determination of the lesion.
46-year-old female patient suffering from primary lung cancer on the left lung lobe. PET / CT examination showed significant systemic skeletal development, the first left-side second rib, clavicle near the left sternal end, a waist, the waist 4, seen at the right iliac focal uptake of radionuclides considered free drug 18F ion oversupply. Review again the next day PET / CT images see systemic bone disappear, the second left head rib, sternum proximal end still on the left clavicle radionuclide uptake, a waist, the waist 4, the original right iliac uptake Movies disappear . Careful analysis of the corresponding parts of CT, see the left side of the second rib head, the left subclavian near side local sternal bone destruction, suggesting bone metastases; 1 back, waist 4, at the right iliac seen round dense cancellous bone shadow, bone island. Upper lobe site of the primary lesion SUV first check value of 7.0 ~ 8.1, 11.3 ~ review every other day 14.2. This is because much of the free ions 18F, 18F-FDG labeled reduced, causing lesions 18F-FDG uptake is reduced.
55 year old woman suffering from primary lung cancer. PET / CT examination showed significant systemic skeletal development, seen at the right side of the skull base focal uptake of radionuclides. The next day to re-review of PET / CT, on the right side at the base of the skull bone uptake shadow disappeared. BMD no CT corresponding parts, structural changes. The patient PET / CT examination first visible hilum lymph nodes a diameter of about 1.0cm radionuclide uptake seen, every other day significantly review this lymph node uptake of radionuclides. Skeletal development obvious when described, is not easy to display small lesions.
60-year-old male patients with esophageal cancer, postoperative 20d. PET / CT examination showed significant systemic skeletal development, the left side of the chest surgery traveling district form ribs radionuclide uptake. The next day to re-review of PET / CT, rib radionuclide uptake shadow disappeared.
68-year-old male patient with colon cancer with liver metastasis. PET / CT examination showed significant systemic skeletal development, no abnormal radionuclide uptake in the liver area. 5 days after re-inspection review of PET / CT, whole body bone development disappears. CT findings a right lower lobe of liver 1.0cm × 2.7cm × 3.4cm at low density lesions were radionuclide uptake.
50 female patients, the right temporal astrocytoma grade I ~ Ⅱ postoperative chemotherapy, has repeatedly applied within one month before the test of recombinant human granulocyte colony-stimulating factor injection, whole body bone development significantly.
2. The impact of the human body itself
due to the body's normal tissues also uptake 18F-FDG. Therefore, understanding the characteristics of different parts of the various manifestations of physiological uptake, master identification methods as well as to prevent, eliminate measures essential for the differential diagnosis of tumors. Head portion, cervico-thoracic, gastrointestinal, urinary, and other physiologic FDG uptake can be carried out, thus affecting the result of the determination.
2.2.1 chest and gastrointestinal concentration analysis of
8-year-old boy, because thymus plump, mild radionuclide uptake.
49-year-old male health checkup. Traveling district found Gastric radionuclide uptake. After eating delayed imaging, the uptake shadow disappeared, confirming a living rational uptake.
Male, 68 years old. Periampullary cancer after one year. It found that the descending colon in the middle there is a limitation of radionuclide uptake, delayed imaging the uptake shadow disappeared, ascending colon segment has emerged wide range of radionuclide uptake. So, it is a physiological uptake.
Male, 74 years old. Due to lung mass line PET / CT examination. Found stomach with little range limitations radionuclide uptake. Eating underwent delayed imaging, the shadow position uptake, no morphological change, the degree of uptake of the radionuclide higher than before, SUV value increased from 4.5 to 5.0 5.7 to 6.6, it is recommended endoscopy, pathology: gastric adenocarcinoma.
Male, 89 years old. Abdominal discomfort line PET / CT examination. The results show: the ascending colon, the left upper intestine appear more highly radionuclide uptake sites. See delayed scan left upper intestine uptake Movies disappeared, ascending colon uptake Movies position, no obvious morphological changes, colonoscopy is recommended. Pathology: colon cancer.
2.2.2 The urinary concentration analysis
male, 44 years old. Colon cancer after surgery. Lower ureteral a visible image focal uptake of radionuclides. Diuretics underwent delayed imaging, the shadow uptake position, shape, size showed no significant change, indicating lymph node metastasis. After surgery confirmed lymph node metastases.
Female, 66 years old. Leiomyosarcoma after 2 years. When there are more retention of radionuclides within the bladder, uterus lesions showed difficulties with diuretics before making imaging, interference within the bladder radioactivity can be basically eliminated, the lesion can be clearly displayed.
Female, 51 years old, after cancer chemotherapy, bladder and cervix affected by radioactive double rectum. In addition to the bladder radioactivity impact, but also consider the interference radioactive intrarectal, intravaginal placing gauze packing scan, displays beneficial anatomy of specific diseases which can be used to accurately position diuretics preclude the diagnosis of cervical lesions. Male, 68 years old, prostate cancer. Diuretics before application after comparison image.
Male, 53 years old. Resection of bladder cancer electricity a year. Underwent delayed imaging catheterization, the bladder tumor lesions showed clear.
2.2.3 Other factors
female, 30 years old. Abnormal uterine cavity radionuclide uptake seen, the developing 10d again, the uptake Movies disappear.
Female, 35 years old. Annex left area shows a diameter of about 1.5cm radionuclide uptake abnormal lesions, a week after the uptake review Movies disappear.
Female, 45 years old, health check. Both breasts were symmetrical uniformity uptake.
Male, 40 years old, health check, see testes showed a uniform concentration of FDG
male, 45 years old, health examination, bilateral thyroid was symmetrical uniformity uptake, thyroid function was normal, no abnormal clinical follow-up for two years .
Male, 53 years old. Health check. Check the morning to climb the mountain.
Male, 58 years old. After liver transplantation. Check before injecting insulin.
3 Results
The above information is explained, reference should analyze the whole body bone scan and CT or MRI clinical history, attention to identify bone metastases and benign bone lesions. As before checking for growth promoting factor and granulocyte drugs like erythropoietin, or lymphoma, systemic myeloid leukemia caused due to diffuse infiltration of bone marrow increased metabolic, and in the PET / CT with the free ions caused by excessive body 18F performance is very similar to bone development, attention should be identified.
18F-FDG may be concentrated in various parts of the digestive tract, including the salivary glands, esophagus, stomach and intestinal FDG accumulation may occur in varying degrees, in accordance with the general performance characteristics of the image and can make the right determination. For parenteral focal uptake Movies to attach great importance to use water in general, oral contrast agents, or the next day and delayed scan imaging, using probanthine pretreatment means, if necessary after eating, the dynamic changes observed help to identify. Enema before the test to avoid taking laxatives. Kidney and urinary system of radionuclides due to the apparent retention of 18F-FDG is excreted by the kidneys without being tubular reabsorption. Ureteral peristalsis due to intermittent presentation cords or dot concentration, and should be next to the aorta, iliac artery lymph node identification. Highest radioactivity bladder, pelvic lesions affect the recognition, and application of water can reduce the development of diuretics. Women Menstruation developing breast milk even point, breastfeeding is more obvious. There is increased uptake of [1] local breast prosthesis during chronic inflammation. Testicular high FDG uptake. Almost all male subjects varying degrees of testicular high FDG uptake. Thyroid FDG imaging. Thyroid FDG few patients developed double-leaf shape, a uniform distribution of radionuclide. Moving muscles will absorb more. 18F-FDG, such as patients in a hurry hurry to come to check, or insulin injections before the examination of the patient, the performance of the whole body skeletal muscle highly concentrated.
In short, radiopharmaceuticals, scanners and subject physiology in vivo uptake of interference, etc. can affect the PET / CT image results, but also to emphasize that here, do not overlook the diagnostic value of CT [2], especially small organ benign lesions, such as the maxillary sinus, thyroid disease and cancer PET-negative patients, attention to different parts, different tissues and organs should carefully adjust the window width and position of CT, to prevent misdiagnosis or missed diagnosis.
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1.2 partial volume effect (Partial volume effect)
because of positron imaging principles and techniques of the dots have a certain degree of expansion source, thus making it a limited resolution. Different systems and different collection methods, will also affect the resolution of the reconstruction algorithm, namely the degree of expansion of the point source. Point source expansion led to partial volume effects.
Correcting the partial volume effect - for PET / CT imaging using the maximum count rate to the target occupying the same plane CT method and size of the lesion shown in the image based on the corrected PET PVE. Jaszczak selected model, the application of radioactive counts returned coefficients (RC) is calculated, the RC is defined as: ratio of radioactivity concentration and the radioactive concentration of the real image focus . RC value varies with the size of the lesion and taken real interest area (ROI) of size, we outline the ROI in clinical CT mediastinal window with the same machine as the standard image, obtained within the ROI average SUV on PET images (Standard Up take value) and the maximum SUV value. RC value obtained by the model, using CRC-15R activity meter, when RC = 1, SUV (corrected) = SUV (maximum). Using PVE correction technology significantly improves the accuracy of PET / CT diagnosis of small lesions of 2.5mm or less.
Effect of metal implants was 1.3 and contrast agents
, for example: tooth fillings, pacemakers, or indwelling needle stapler, etc., due to the higher absorption of photons, can result in an increase in CT value and artifacts strip. Such a PET performed with the CT image after attenuation correction , which is generated in the overcorrection region, imaging agent activity overestimated, resulting in false positive results . But no such mistake on PET images without attenuation correction,Interpretation should be noted. Intravenous or oral contrast agent, blood vessels can be enhanced on CT images, gastrointestinal tissue and marked, although these agents can improve the contrast CT image quality, but affect both qualitative and quantitative measurement of the PET image, which metal implants the similarly affected. Due to the high concentrations of the contrast agent can be shielded photon positron annihilation produced, resulting in problems of excessive correction, it is necessary to pay attention to the concentration of the contrast agent. Dose and time directly affects the gastrointestinal filling the scope and extent. Recommended concentration oral contrast agent is from 2% to 3%, a volume of 800 ~ 1000ml, 2/3 divided doses before checking, the remaining portion of the front check taking 5 ~ 10min (visualize the stomach).
Exceeds 1.4 PET / CT scan the field of view
of patients larger body, hands on both sides of the body or the scan: (such as malignant melanoma and head and neck cancer scans), CT scan beyond the field of view (horizontal field of view of CT 50cm, lateral field of view of 70cm PET), resulting in a corresponding region on the PET images without attenuation correction, thereby causing a deviation of the attenuation-corrected image, and thus the value of SUV underestimate these regions, generating truncation artifact; lead generation CT image edge streak artifact, thus generating high activity profile cut edges, may lead to misinterpretation, attention should be scanned and observed image.
1.5 artifacts body and organ movement generated
when the PET / CT image acquisition, whether it is the patient body movement, the patient or the organ physiological movement, will affect the quality of fusion PET / CT image. The influence of body movement can refer patients to avoid, but the physiological movement is inevitable in the collection, the most important physiological movement is breathing exercises. In general, these motion artifacts in the region of mainly surrounding the heart and diaphragm. Because PET acquisition time is very long (15 ~ 20min), free breathing when the patient acquired, and CT image acquisition only one phase image when breathing, thus differences CT and PET images of the anatomical site is present on the PET / CT image, is formed artifacts.
Due to respiratory motion caused by a mismatch CT and PET, attenuation correction will lead to positive pulmonary lesions of errors, their impact on small lesions more obvious than large lesions. Due to respiratory motion, the bottom of the lung lesions can reach a maximum displacement 3cm, But will also focus on the PET images increase in size, thereby reducing the value of SUV of small lesions. More respiratory artifact known liver lesions as well. Because breathing exercises can make the mistake of liver lesions appear at the bottom of the lungs, similar to pulmonary nodules. The most common respiratory artifacts arcuate diaphragm is above the cold zone, occurs when the artifact, CT images are generally acquired deep breathing, the maximum displacement of the diaphragm, so the diaphragm around the PET image representative of normal organs the air instead of the soft tissue, thus underestimating the CT attenuation coefficient, and further in the lungs - the arc is generated at the junction compartment cold zone. When these artifacts influence appears suspicious diagnosis, we took a single bed localized lesions imaging method that breath-hold fast PET 3D acquisition (20 ~ 30s), a proven, have achieved very good results. 2. The imaging agent of influence on image quality imaging agent is a necessary condition for the developing of PET / CT. The biological nature of the tracer, the image PET / CT obtained reflects the distribution of the tracer in the body. 18F-FDG (FDG) is the most widely used tracers in clinical, more than about 90% of domestic and PET / CT imaging, are obtained using this kind of developer, including tumor, brain and the blood vessel application. 2.2 18F-FDG in vivo distribution in the tumor, hypoxia inducible gene can be overexpressed on the cell membrane to promote glucose transporters, and further such that lack of oxygen metabolism of tumor cells, 18F-FDG is the use of this principle and imaging . However, PET / CT detected information to the function, but also represents the initial phase of glucose metabolism, it also has some differences with the distribution of normal glucose metabolism in normal distribution in vivo. Many organizations can ingest body 18F-FDG, skin, adipose tissue, muscle, there is a certain intake; a high degree of brain uptake. When checking if the patient is high insulin levels, it will lead to 18F-FDG into muscle and other tissues, affecting the image quality of PET / CT. Generally considered unsuitable for PET / CT imaging in the patient's blood glucose level of more than 200mg / dl. Therefore, fasting is essential to check before 4 to 6 hours, otherwise it will lead to poor image display.
Since 18F-FDG excreted through the kidneys, renal pelvis, calyx, urine bladder be interference 18F-FDG agglomeration, has a great influence in the determination of local lesion, therefore, for the examinee suspected urinary system diseases, diuretics before checking orally or by injection, Nursing and drink plenty of water, then a partial scanning delay after voiding, application of these methods to improve the imaging results.
In short, PET / CT is currently more popular in clinical applications and in-depth, enriching the diagnosis is based on clinical imaging in the diagnosis of disease, and to obtain the desired image data is crucial to ensure the quality of diagnosis, should have a PET / CT scan results in factors artifacts generated understand its possible impact on the scanned image effect, take timely and effective corrective measures to reduce or completely avoid confounding factors in order to obtain the best image quality.
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Reporter: PET / CT early detection of tumors and tumor stage and grade it?
Fanzhu Ren: tumors typically undergo mutations - changes in biological macromolecules - metabolism - structural changes in four stages, the clinical symptoms associated with the structure changes occur, usually at this time of the tumor is close to the middle and late.
Mainly by tumor metabolic imaging of certain radionuclides (e.g., 18F) of these metabolic substrates labeled tracer, or the like, and visually displayed in the form of an image, can be accurately dynamically reflect tumor cells and normal tissue metabolism difference. When still morphology did not change and do not have any clinical symptoms, PET / CT can be performed on the tumor early diagnosis of involvement of each organ and tissue were evaluated to achieve tumor accurate clinical staging, treatment options, efficacy the purpose of monitoring.
Reporter: PET / CT examination What are the indications?
Fan Zhuren: Early diagnosis of cancer; the differential diagnosis of benign and malignant tumors; grade malignant tumor staging; look for the primary tumor; treatment response, to assess the efficacy of diagnosis and prognosis; guided tumor puncture biopsy and interventional therapy; radiation oncology treatment planning to develop; early diagnosis of coronary heart disease, myocardial infarction after myocardial survival judgment; senile dementia diagnosis and assessment of disease, lesion detection and localization of epilepsy, Parkinson's disease diagnosis and identification; high-end health examination, early detection or exclusion of tumors malignant disease.
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