Gastrointestinal Bleeding Scintigraphy in the Early 21st Century.

Gastrointestinal bleeding scintigraphy performed with (99m)Tc-labeled autologous erythrocytes or historically with (99m)Tc-sulfur colloid has been a clinically useful tool since the 1970s. This article reviews the history of the techniques, the different methods of radiolabeling erythrocytes, the procedure, useful indications, diagnostic accuracy, the use of SPECT/CT and CT angiography to evaluate gastrointestinal bleeding, and Meckel diverticulum imaging. The causes of pediatric bleeding are discussed by age.

Nuclear medicine procedures in the diagnosis of NET: a historical perspective.

Novel diagnostic tools and therapies have emerged as a result of the continuous endeavors relating to neuroendocrine tumors (NETs). Nuclear medicine plays a pivotal role in the imaging and treatment of NETs. Somatostatin receptor analogues and metaiodobenzylguanidine remain front-line single-photon emission computed tomography (SPECT) radiotracers in the imaging of NET; their utility has been augmented by the increasing availability of SPECT/CT. Positron emission tomography has been growing rapidly in the imaging of NETs, paralleled by great efforts toward the development of new tracers. Hybrid imaging will play an important role in the future of NETs.

The evolution of nuclear medicine and the musculoskeletal system.

This article reviews the evolution of nuclear medicine in the evaluation of the musculoskeletal system over the past hundred years, from autoradiography and Geiger counters and rectilinear scanners to sophisticated imaging devices that provide both functional and morphological information. Initially synonymous with bone scanning, radionuclide evaluation of musculoskeletal disorders now includes gallium, labeled leukocytes, FDG, and fluourine-18, indications and applications of which are reviewed.

The contribution of medical physicists and doctors in Aberdeen to the evolution of modern medical imaging--SPECT, PET and MRI, 1965-1992.

From the beginnings of medical imaging with radioactivity, an account is given of the development in Aberdeen of Computed Tomography (CT) scanners in Nuclear Medicine, and their clinical value, leading to present-day gamma-cameras. The introduction and clinical use of the cyclotron and Positron Emission Tomography (PET) imager in Aberdeen, has led to a national programme for the cancer patients in Scotland. Early animal work with electron magnetic resonance, which developed into a programme towards nuclear magnetic resonance of water, and then to a quest to build the first clinically-useful whole-body MRI, is described. Successful diagnostic images obtained with it have led to the present-day worldwide use of the MRI technique.

Perfusion thresholds in human cerebral ischemia: historical perspective and therapeutic implications.

After middle cerebral artery occlusion (MCAO) in the laboratory animal, the ischemic penumbra has been documented as a severely hypoperfused, functionally impaired, but still viable cortex which can regain its function and escape infarction if it is reperfused before a certain time has elapsed. The penumbra surrounds the ischemic core of already irreversibly damaged tissue, and is progressively recruited into the core with increasing MCAO duration. In the animal, the threshold of cerebral blood flow (CBF) below which neuronal function is impaired and the tissue is at risk of infarction is around 22 ml/100 g/min (approximately 40% of normal) in the awake or lightly anesthetized monkey, and around 30--35 ml/100 g/min in the cat and the rat. The threshold of CBF below which the tissue becomes irreversibly damaged and will progress to infarction depends on the duration of ischemia, and is around 10 ml/100 g/min for 1--2 h (approximately 20% of normal) and around 18 ml/100 g/min for permanent ischemia in the monkey. Mildly reduced CBF down to the 40% threshold (termed 'oligemia') is normally well tolerated, and the affected tissue is not at risk of infarction under uncomplicated conditions (in the animal, however, selective neuronal death may occur even with only mildly reduced CBF values, but this sequela of stroke seems an exceptional encounter in man). Classic studies with carotid artery clamping in man have provided estimates for the penumbra threshold at around 20 ml/ 100 g/min for the whole brain, but only recently have imaging studies allowed to document the existence of the penumbra in acute stroke and given estimates of local CBF thresholds. With PET, the penumbra is characterized by a reduced CBF, an increased oxygen extraction fraction, and a relatively preserved oxygen consumption (CMRO(2)). In a series of PET studies performed 5--18 h after stroke onset, we have determined the threshold for penumbra to be around 20 ml/100 g/min, and documented that the extent of neurological recovery is proportional to the volume of penumbra that eventually escaped infarction. Within this time interval, the thresholds for irreversible damage were around 8 ml/ 100 g/min for CBF and around 0.9 ml/100 g/min for CMRO(2). Recent studies with diffusion-weighted and perfusion MR have reported similar relative thresholds for CBF of about 50 and 18% for penumbra and core, respectively. Although it is likely that the threshold for irreversibility will be lower with shorter duration since clinical onset, this has not been documented thus far. Because saving the penumbra will improve clinical outcome, it should constitute the main target of acute stroke therapy. We found evidence of penumbra in about one third of the cases studied between 5 and 18 h after onset, and as late as 16 h after symptom onset in occasional patients, suggesting the therapeutic window may be protracted in at least a fraction of the cases; similar experience has recently accrued from diffusion-weighted MR and perfusion MR. In the remaining patients, there was evidence of early extensive damage or early spontaneous reperfusion, which would make them inappropriate candidates for neuroprotective therapy. Recent evidence from PET studies of relative perfusion performed within 3 h of onset suggests that early thrombolysis indeed saves the tissue with CBF below a critical threshold of 12 ml/ 100 g/min, with a correlation between the volume of such tissue escaping infarction and subsequent neurological recovery. Thus, mapping the penumbra in the individual patient with physiologic imaging should allow to formulate a pathophysiological diagnosis, and in turn to design a rational management of the stroke patient and to increase the sensitivity of drug trials by appropriate patient selection.

[Nuclear medicine in vivo and functional imaging. Historical perspective]. / La médecine nucléaire in vivo et l'imagerie fonctionnelle. Perspective historique.

Nuclear Medicine is the application of radioactive materials to the diagnosis and treatment of patients and the study of human disease. The field had its beginning with the discovery of radioactivity by H. Becquerel in 1896 and the tracer principle proposed in 1913 by G. de Hevesy who used a naturally occurring radioactive isotope of lead to obtain information regarding certain aspects of calcium metabolism in plants. The actual development is more recent. F. and I. Joliot-Curie just after the discovery of the artificial radioactivity predicted in their visionary Nobel conference in 1935 the future applications of radioisotopes in biology and medicine. The development of Nuclear Medicine was made possible by the possibility of producing routinely the radioisotopes after World War II and by the development of suitable detectors: moving detector devices (scanners) then gamma cameras after 1957. Nuclear Imaging is today a unique tool for the in vivo investigation of the biochemical functioning of an organ. Two techniques are in rapid development, SPECT (single photon emission computed tomography) and PET (positron emission tomography).