CURRENT CONTENTS:
Technetium generators
ECG-gated myocardial SPECT
Parathyroid scintigraphy
A.C. to improve SPECT imaging
DEXA for bone mineral assessment
Fluorine-18 PET (positron emission tomography)
Gadolinium contrast agents for MRI
"DOG"-scans (computed axial DOG-graphy)
Authors' Note: SPECT (Single Photon Emission Computed Tomography) imaging of the myocardium (heart muscle), performed at rest and with stress (exercise or drug infusion) is currently the most frequent test performed in hospitals' nuclear imaging departments.
The 3-dimensional images, a type of computed tomography, are produced with a camera which detects the emission of the single-energy gamma rays following an injection of a radionuclide. By connecting the patient to a system for recording the ECG (electrocardiogram), the images can be "gated", i.e. divided into segments of the cardiac cycle; these show contraction of the ventricles, following each of two injections of the imaging agent. A muscle region showing identically poor blood flow (perfusion) and contractile function at rest and stress represents prior heart damage, and is unlikely to respond to therapy.
Authors' Note: Attacks of renal colic (spasmodic intermittent pain) may occur due to blockage of urine flow by stones in the ureters. In adult patients, stones consisting of calcium salts are most likely. If a high serum calcium level is found (this situation prevails in only a minority of cases of kidney stones), overactivity of the tiny parathyroid (PT) glands may be responsible. Milder cases of excessive parathyroid hormone secretion may also occur without symptoms, but can lead to loss of bone mass and increased risk of bone fracture.
A single functioning adenoma (benign tumor) of one of the PT glands is most commonly responsible, but hyperplasia (overgrowth) of all four glands may also result in inappropriate PT hormone secretion, detected by increased blood levels. The radiotracer Tc-99m sestamibi is taken up selectively by overactive PT glands, and may help plan surgery to explore the neck and remove the tumor.
Authors' Note: Absorption of rays by body tissues complicates the interpretation of medical imaging with nuclear techniques. ‘Hybrid' scanners combine the nuclear camera with a CT x-ray unit that provides maps of attenuation; this technique for correction of attenuation (known to workers in the field as A.C.), makes the nuclear scan more accurate in the detection of various lesions, in particular, abnormalities in blood flow to the heart muscle, and studies of deeply-located tumors, e.g. somatostatin scans.
The combination of the two scanners (nuclear and X-ray CT) has been given the puzzling name “SPECT-CT”.
Authors' Note: DEXA, or Dual Energy X-ray Absorptiometry, is a simple standardized imaging test to assess bone mass in the context of osteoporosis. It actually measures bone mass in a peculiar form, i.e, mass per unit area (rather than volume) of tissue; differential attenuation (blocking by tissue) for the 2 photons of different energies is assessed for each spatial element in a planar field. The technique is however, excellent for serial tests in the same patient, and is now used so widely that its results are regarded as synonymous with Bone Mineral Density (BMD).
Authors' Note: Although the element gadolinium (Gd) is itself toxic, its highly bound chelates make excellent adjunctive agents for diagnostic imaging procedures using magnetic resonance (MR), as they change the magnetic properties of structures with high rates of blood flow, yet allow 'negligible' release of the metal into tissue during the interval following a single intravenous injection. Non-toxic chelates of metallic elements are normally rapidly cleared from the body by urinary excretion.
In the late 1990s, a ‘new’ disease, nephrogenic systemic fibrosis was found in a small minority of patients, mostly with severe kidney disease, who had received these contrast agents. The problem can be avoided by a simple screening of relevant patients for a history of kidney disease or renal impairment.
Authors' Note: The confusing terminology for advanced, i.e. 3D medical imaging, uses acronyms that may be historically based or poorly explained. The development of a method of imaging known as ‘DOGgraphy’ is apocryphal.
CAT: computerized axial tomography, X-ray imaging of a body section; better described in modern terms as ‘x-ray CT’
PET: positron (dual-photon) emission tomography; a Nuclear Medicine technique involving prior injection of a positron-emitting radionuclide ('isotope'); becoming an important modality in cancer assessment
Holography: processing of fields of light or other radiation scattered from objects; well developed with lasers, but with limited current application in medical imaging.
Here's a LIST OF LINKS to collections of intriguing poems (over 200 of these!) on medical/dental topics, updated to December 2024.
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To resume the sequence of daily titillations on our related blog "Daily Illustrated Nonsense", click HERE. Once you arrive, you can select your time frame of interest from the calendar-based listings at the bottom of the page, and check the daily offerings for any month from the start of 2020 until December 2024.
As of December 2024, there are 1800 unique entries available on the daily blog, displaying individual poems (often illustrated) and wordplay, but also with some photo-collages and parody song-lyrics. Most of their key elements are also presented here on "Edifying Nonsense" in topic-based collections, such as this one. The "Daily" format also has the advantage of including some song-lyrics, videos and other material that are not shown here on this topic-based blog.
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