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The bone is continuously in a remodelling process. Bone mass is maintained in a continuous balance between its destruction and formation. Bone remodelling proceeds in a highly regulated cycle in which osteoclasts adhere to bone and subsequently remove it by acidification and proteolytic digestion and the osteoblasts secrete a organic matrix which is calcified into new bone. Bone remodelling is the cellular basis of bone metabolism. Pathological changes in many metabolic bone diseases can be explained by abnormalities at some point of the remodelling cycle. The mechanisms of regulatory bone metabolism involve the availability of a number of minerals and ionic homeostasis, systemic hormones and numerous local factors. In this work the general pattern of bone remodelling and the cellular mechanisms of bone resorption and formation are briefly described. The role of systemic and local factors in the regulation and coupling of these two processes is also reported.

The prognosis for patients with chronic coronary artery disease and severe left ventricular dysfunction is poor, despite advances in different therapies. The assessment of myocardial viability has become an important aspect of the diagnosis, prognosis and management of patients with ischemic cardiomyopathy. Patients with left ventricular dysfunction, with a substantial amount of severely ischemic myocardium are at highest risk, and are likely to benefit from coronary revascularization. Patients with predominantly scar tissue should be treated medically. Multiple imaging techniques have been developed to assess viable and nonviable myocardium by evaluating perfusion, cell membrane integrity, glucose metabolism, fibrosis and contractile reserve. PET FDG-F18, myocardial perfusion scintigraphy (with (201)Tl and (99m)Tc), dobutamine stress echocardiography and more recently magnetic resonance have been extensively evaluated for assessment of viability and prediction of clinical outcome after coronary revascularization. In general, nuclear imaging techniques have a higher sensitivity for the detection of viability, whereas techniques evaluating contractile reserve have higher specificity (with lower sensitivity). Magnetic resonance has a high diagnostic accuracy for assessment of the transmural extent of myocardial scar tissue. The aim of this article is to review the role of Nuclear Medicine in assessing myocardial viability and risk stratification in patients with advanced left ventricular dysfunction, and to compare it with other imaging modalities.

Purpose: To show the value of bone scintigraphy in the diagnosis of metastatic calcification in end-stage renal insufficiency., Material and Methods: The authors present a fifty-one-year-old male with terminal renal insufficiency of hypertensive renovascular etiology, on hemodialysis for the last 10 years, referred for a bone scan because of osteoarticular complaints, and no other associated symptoms or findings on physical examination., Results: Whole body bone scintigraphy images (HMDP-99mTc, 925MBq), showed increased uptake in the lower half of both lungs, the stomach and renal parenchyma, compatible with metastatic calcification., Conclusions: Bone scintigraphy, due to its high sensitivity, even in the detection of early changes, might be a useful instrument in the initial evaluation and follow-up of patients with high risk of developing metastatic calcification.

Osteoid osteoma is the third most common benign bone tumor. It usually affects the diaphysis of long bones, especially the femur or the tibia. This paper presents the case of a 22-year-old male patient, with pain in the left knee. The x-ray and ultrasound of the knee were normal. The three phase bone scintigraphy revealed a focal uptake in the mid shaft of the left femur, strongly suggestive of osteoid osteoma. This case shows the significant role of bone scintigraphy in the diagnosis of an osteoma osteoid with atipical presentation.

Coronary heart disease is the main cause of death in developed countries. At least 25% of coronary patients have sudden death or nonfatal myocardial infarction without prior symptoms. Risk stratification identifies patients at risk for coronary events. Evaluations should begin with patient's clinical history, but some patients benefit from noninvasive cardiac imaging evaluation. The aim of this paper is to review the main indications for noninvasive cardiac imaging in risk assessment of asymptomatic patients.