SPECT Test

Single-photon emission computed tomography (SPECT) is a nuclear medicine imaging technique that frequently uses gamma rays radioisotope or gamma camera to take the 2D or 3D image for diagnosis of major artery internal structure, blood clot, plug formation, small vessel block in the heart and brain, ischemia, stroke, nerve structure, nerve damage, bones structure, bone fracture tumor, cancer in a tendentious joint, ligament, muscle cancer, tumor, ulcer in the stomach, ICU critical condition diagnosis especially heart, lung, liver, kidney, and peripheral artery disease. It also helps minimal resection of vertebrae, maximal protection of an articular process, vertebral artery, disc protrusion, disc sequestration, disc herniation, PLID, and spinal cord as well as total resection of a spinal tumor.

The technique needs delivery of a gamma-emitting radioisotope means gamma camera (a radionuclide) injection into the bloodstream through the vein. Then it travels through the bloodstream and produces a 3-dimensional image of the distribution of a radioactive tracer (sometimes called a probe). It can provide true 3D information typically presented as cross-sectional slices image, then it can be freely reformatted or manipulated when required. On occasion, the radioisotope is a simple soluble dissolved ion, such as an isotope of gallium(III) is frequently used. Most of the time, though, a marker radioisotope is attached to a specific ligand to create a radioligand, whose properties bind it to certain types of tissues to take the image.

Indications

Indications for SPECT imaging are developed by imaging revulation, and some important ones are listed below. These indications include:

  • Evaluating patients with suspected dementia
  • Localizing epileptic foci preoperatively
  • Diagnosing encephalitis
  • Monitoring and assessing vascular spasm following subarachnoid hemorrhage
  • Mapping of brain perfusion during surgical interventions
  • Detecting and evaluating cerebrovascular disease
  • Predicting the prognosis of patients with cerebrovascular accidents
  • Corroborating the clinical impression of brain death
  • Several indications in the field of oncology are listed in this article.

In addition, the American Society of Nuclear Cardiology has developed an extensive list of indications for cardiac SPECT studies. Some notable indications include:

  • Evaluating patients for coronary artery disease.
  • Assessing treatment response and guidance of future therapy in patients with coronary artery disease, cardiomyopathy, and heart failure.
  • Diagnosing coronary artery disease in patients unable to perform a standard exercise stress test.
  • Pre-surgical evaluation of patients with suspected or confirmed coronary artery disease.

SPECT scans are also indicated for non-cardiac and non-neurological conditions such as osteomyelitis, spondylolysis, parathyroid disease, pulmonary embolism, and abscess localization.

Thoraco‐abdominal aorta

  • Diagnosis of congenital and degenerative aortic diseases
  • Assessment of acute aortic injuries and dissections
  • Evaluation of visceral arteries (coeliac, superior mesenteric, and renal arteries)
  • Preoperative planning and follow up
  • Tumor staging and surgical planning

Renal arteries

  • Assessment of anatomy for donor transplants
  • Diagnosis of renal artery stenosis in hypertensives or deteriorating renal function
  • Assessment of renal arteries post‐intervention (renal artery stenting)

Peripheral arterial system

  • Assessment of peripheral vascular disease
  • Assessment of bypass grafts

Carotid/intracranial circulation

  • Characterization of the atherosclerotic disease
  • Assessment of aortic arch vessels
  • Verification of internal carotid artery stenosis
  • Preoperative planning of endovascular and surgical treatment of intracranial aneurysms and vascular malformations

Cardiac imaging

  • Atypical chest pain
  • Patients with intermediate-risk
  • Young patients with a high risk for coronary disease
  • Coronary artery anomalies
  • Non‐invasive follow‐up following percutaneous transluminal angioplasty and stenting
  • Assessment of myocardial scars, aneurysms, tumors, and thrombi
  • Assessment of coronary artery bypass grafts
  • Assessment of the pulmonary veins before and following radiofrequency ablation
  • the diagnostic accuracy of coronary artery disease; the prognostic value of coronary artery disease with regard to the prediction of major cardiac events; detection and quantification of coronary calcium and characterization of coronary plaques.
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Bone and spine

  • Intraspinal or intervertebral foramen cervical dumbbell tumors,
  • tumors beyond the intervertebral foramen
  • Spinous process, supraspinal and interspinous ligament,
  • The contralateral paravertebral muscle thus
  • Investigate stability and flexibility problems of cervical vertebrae and
  • alleviates cervical stiffness.
  • Reveals the contour of the tumor as well as compression upon the spinal cord, the extent of spinal edema as well as mutual relationships among the tumor, dura mater, and nerve root [,].
  • At the same time, VRT is conducive to analyzing tumors at different levels for intratumoral vascular route and evaluating infliction and erosion extent of vessels thus assessing neurosurgical difficulties and risks.
  • Owing to its high resolution based on the reconstruction thickness at the sub-millimeter level,
  • VRT formulates images from different perspectives for locating vertebral artery, confirming vascular route and compression degree as well as visualizing peripheral vessels around the tumor.
  • sparing nerve roots: nerve roots above the tumor or enwrapped by the tumor could be dissected and protected, while nerve roots coursing through the tumor should be resected due to their involvement in the tumor original.

Analysis of coronary artery lesions

Systematic analyses of a coronary artery MDCT study took into consideration the following steps:

  • (1) Analysis of images reconstructed from different phases of the cardiac cycle, in order to choose those where the coronary arterial tree is best filled with contrast and where movement artifacts are the least.
  • (2) A complete review of axial images that constitute the cardiac volume, paying attention to cardiac anatomy, degree of opacification of chamber and walls of the heart, and aspect of extracardiac structures.
  • (3) Optimization of images aimed to improve the visualization of coronary arteries, by using specific post-processing protocols.
  • (4) Analysis of the coronary artery tree, for which is fundamental the following systematization:
  • □ Examination of the anatomical distribution of coronary arteries aimed to identify normal variants and congenital abnormalities of the origin of vessels.
    □ Detection and localization of coronary artery lesions, carefully avoiding sections and angulations or interposed structures with potential image artifacts.
  • □ Evaluation of composition and morphology of the lesion. In regard to the composition of the plaque, a distinction was made between calcified and non-calcified plaques. Plaques with a mean attenuation of 130 HU or greater were graded as calcified, whereas plaques with a mean attenuation of less than 130 HU were graded as non-calcified. Calcified plaques were identified on nonenhanced scans, and non-calcified plaques were identified on contrast-enhanced scans.
  • □ Qualitative and quantitative assessment of obstruction of the vessel caused by the lesion.

A classification of atherosclerotic coronary artery lesions is possible by applying this systematic analysis of . This classification can be made according to the following aspects:

  • The number of vessels involved.

□ The location: proximal, middle, or distal portions of the vessel.

□ The extension of the lesion: focal or diffuse.

□ The degree of obstruction.

a. Non-significant stenosis (less than 60 % of the vessel lumen, including mild and moderate degrees of obstruction).

b. Significant stenosis (equal or more than 60 %, including critical subocclusive and occlusive lesions.

□ The components of the lesion:

a. Non-calcified, mixed, or “soft” lesions.

b. Calcified lesions: The calcium component of the lesion can be focal, diffuse, eccentric or concentric.

Currently, MSCTA has been applied for late-phase image reconstruction in the following ways [] multiplanar reconstruction (MPR), shaded surface display (SSD), bone scintigraphy, maximum intensity projection (MIP), and recently volume rendering technique (VRT) which surpass its predecessors as a supreme technique in reconstructing three-dimensional spatial relationships.

Contraindications

SPECT imaging alone has no absolute contraindications; however, patients may rarely experience allergies to the tracer compound. most frequently, contraindications for SPECT imaging are said to be the underlying procedure instead of the SPECT scan itself. for instance, a cardiac assay augmented with SPECT carries equivalent risks and contraindications as a routine assay. Clinicians should also carefully consider the risks of radiation exposure when referring patients that are pregnant for SPECT, and radioactive iodine isotopes should be avoided in these patients also thanks to fetal iodine uptake.[8] Finally, some obese patients may exceed the load limit of the scanner apparatus.

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Equipment

3D-SPECT imaging requires a rotating multi-headed gamma camera, a collimator, and a radio-labeled tracer specific to the target tissue. the essential function of the camera is the detection of photons produced by gamma decay of the tracer compound, which is emitted in altogether directions from the patient. The collimator functions to filter these photons, allowing only particles that are parallel to the detector through. The collimator, therefore, focuses on the radiation, and collimator selection influences the sensitivity and determination of the ultimate image.

The number of gamma camera heads increases the resolution of the ultimate image and reduces the quantity of time required for the scan. However, high-quality images are often produced with single-headed cameras by skilled medical physicists and nuclear radiologists.[3][9]

Personnel

The American College of Radiology offers technical standards for the roles and responsibilities for personnel involved within the safe and effective administration of a SPECT study. The personnel required for a secure and effective SPECT scan generally include:

  • Clinician
  • Nuclear medicine technologist
  • Nuclear pharmacist
  • Medical physicist
  • Radiation safety officer
  • A board-certified nuclear cardiologist or nuclear radiologist should be present to supervise the study.

Preparation

Patients should be instructed to avoid caffeinated beverages for a minimum of 12 hours before the study. this is often because caffeine interferes with the action of vasodilatory medications which will be administered during the study. Caffeine also affects cerebral blood flow and may negatively influence cerebral SPECT imaging. The patient should also avoid dipyridamole and other phosphodiesterase-3 inhibitors for a minimum of 48 hours to avoid a synergistic vasodilatory effect, which can produce an unsafe drop by vital signs. Finally, all patients should be made nil per oral for a minimum of 3 hours before the procedure and asked to void urine beforehand to maximize comfort.

Technique

First, the patient is injected with a radio-labeled tracer compound selected by the nuclear pharmacist. For cerebral studies, the patient will first be seated in a quiet, dimly lit room and asked to not read or represent a minimum of 10 minutes before tracer injection. If the patient requires sedation for the procedure, it should be administered after the tracer, if possible. Following injection, there’s a variable waiting period to permit the tracer to circulate and be haunted by the target tissues. This waiting period is often as long as 90 minutes for cerebral studies or as short as a quarter-hour for cardiac stress tests. Wait periods for a specific study also will vary counting on tracer selection and dose.

Once the waiting period has elapsed, the patient will then be moved into the detector apparatus. If the patient is undergoing cardiac stress testing, they’re going to tend to cardiac stimulants like atropine in accordance with standard stress testing protocols. Both cerebral and cardiac studies may utilize vasodilatory medications to assess tissue perfusion. Once the patient is in situ and therefore the necessary medications are administered, the detector will rotate around the patient taking planar scans every 3 to six degrees, which can be combined to supply the ultimate 3D image. Specific imaging protocols vary and should require one scan, as in brain imaging, or several scans could also be taken at set timing intervals, as in stress/rest imaging for cardiac SPECT.[11] While SPECT is in a position to supply detailed information about the issues, it’s not without limitations. Small metabolic abnormalities which will be detected on SPECT are often difficult to localize without corresponding anatomical imaging. To avoid these difficulties, a combined SPECT/computed tomography protocol has been developed, wherein functional and anatomical abnormalities detected by the SPECT study also are imaged simultaneously on computerized tomography.

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Certain SPECT protocols which will be used to scale back radiation exposure and hazards include the following

  • Appropriate patient selection for SPECT imaging supported by clear indication will reduce unnecessary radiation exposure to patients and also as prevent the likelihood of a mistake occurring.
  • Technetium-99m based SPECT protocols (sestamibi and tetrofosmin) offer lower patient radiation exposure than thallium-201 (stress/redistribution and stress/reinjection) protocols. For the evaluation of pain and therefore the diagnosis of ischemia, technetium-99m based protocols are safer and preferred.
  • Radiotracer dose should be weight-based to optimize the radioactivity dose required.
  • Cadmium zinc telluride detectors within the imaging camera are more sensitive to the incident radiation, and these detectors have better energy and spatial resolution. The utilization of cadmium zinc telluride cameras and Anger cameras can optimize radiation techniques.
  • SPECT stress-only protocols using technetium-99m labeled radiotracers may reduce radiation exposure by 25% as compared to typical rest/stress studies. Stress-first imaging is advisable in subjects who are good imaging subjects and who don’t have a high pretest probability of an abnormal study. this is often particularly important and feasible in young patients, particularly those with low to moderate pretest probability of arteria coronaria disease.
  • The 2-day rest/stress technetium-99m (14 mSv) is often optimized to either stress only (7 mSv) or single-day rest/stress protocols (10 mSv), thereby minimizing radiation exposure.
  • Image acquisition practices are often optimized to lower the quantity of required radioactivity. In cooperative patients, the radiotracer dose is often reduced by lengthening acquisition times. it’s important to position the camera as close as possible to the patient throughout the acquisition to lower the specified radioactivity dose.
  • Newly developed reconstruction algorithms are ready to maintain image quality from SPECT studies, despite reducing the radiotracer dose. employing a novel wide-beam reconstruction algorithm, superior image quality is often acquired with a 50% reduction in radiation dose.
    If a scanner utilizes a CT scan for attenuation correction, the acquisition protocol is often optimized to use the rock bottom dose available for attenuation correction (rod-source).
    Software developments like resolution-recovery techniques are ready to significantly reduce radiation exposure.

Side Effects

Potential adverse effects of contrast medium injection and radiation exposure side effects were explained to all the patients by a radiologist, and written informed consent was obtained before the procedure.

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References