Radiation measurement units have undergone a change from Rads and Rems to Grays and Sieverts. However, radiobiology literature uses both systems, resulting in confusion for Radiologists. Radiation exposure is quantified by the unit Kerma which is currently expressed in Grays and Sieverts. In this review, we attempt to explain both the earlier units and the present system of SI (System International) units. This review also appraises the reader that human beings live under significant doses of radiation from natural sources, such as the naturally occurring radioactive gas radon, besides that from man-made sources such as X-rays, radioactive medication and nuclear installations. The biological effects of radiation had been studied and documented within few years of the discovery of X-rays and further information has consequently been available from longitudinal studies on populations affected by the atomic bomb. Biological effects are classified as deterministic (or certainty effects) and stochastic effects. Both deterministic and stochastic effects may either result in changes in organs (somatic effects) or in the genes (genetic effects). Deterministic or certainty effects are directly related to a known dose of radiation and have a dose threshold and their severity is also dose related. Stochastic effects are random events which are not dose related but their probability increases with an increase in the radiation dose. Carcinogenesis and genetic mutations are stochastic effects. The radiosensitivity of organs varies, therefore the various doses at which the deterministic effects on different organs occur are reviewed. The doses likely to be associated with 'risks of cancer' are also enumerated and the doses related to genetic mutations are also discussed. The effects on the fetus are both somatic and genetic and the most radiosensitive period is 8-17 weeks of gestation. The safety of radiographic imaging is discussed with reference to doses delivered in common radiological studies. Radiation doses permissible during pregnancy in the general population and in radiation workers are also highlighted.

Aim: To evaluate the accuracy of Magnetic resonance cholangiography (MRC) in defining the extent of biliary ductal involvement in malignant hilar obstruction and its usefulness in planning percutaneous palliative drainage. Materials and Methods: Fifteen patients with malignant hilar obstructions were examined with MRC. All patients underwent Percutaneous Transhepatic Cholangiography (PTC) and biliary drainage. The site of obstruction and a hypothetical drainage plan based on the MRC findings were compared to the PTC and the actual drainage performed. Results: MRC accurately predicted the site of obstruction in 11 out of 14 patients (78 percent). One patient had an inadequate MRC. The hypothetical drainage plan based on MRC matched the actual drainage in 12 out of 14 cases (85 percent). Conclusion: Preprocedural MRC is a valuable tool for defining the site of obstruction. It provides a 'road map' for performing percutaneous biliary drainage.

Objectives: The purpose of this study is to evaluate the role of MRI as an investigative modality in white matter diseases and to document its value in early diagnosis and management. This was done by studying the MR appearances of various white matter diseases encountered in our hospital with special reference to multiple sclerosis and correlating it with the clinical presentation. In addition, the most common diseases among them were identified. Materials and Methods: Forty patients with a strong clinical suspicion of demyelinating disorder were evaluated by MRI using 0.5 Tesla (Signa Contour, GE) scanner in a prospective study period of 2 years. Images were obtained in sagittal, axial and coronal planes using SE T1, PD and T2 and FLAIR sequences. Slice thickness of 5mm, FOV of 24 x 24 and 256 x 192 matrix were used. Results: Demyelinating foci were demonstrated with a high degree of accuracy on MR as prolonged T1 and T2 relaxation times, the site of the lesion varying in different disorders. Multiple sclerosis accounted for the majority of cases (37.5 percent) followed by acute disseminated encephalomyelitis (15 percent). Other causes like infections, toxic causes, periventricular leukomalacia and leukodystrophies comprised the remainder of the cases. In multiple sclerosis, majority of the patients presented in the third decade of life with a definite female preponderance (M:F-1:2). The most common symptom and site of involvement were visual impairment (73.3 percent) and periventricular area (80 percent) respectively. Conclusion: MRI due to its excellent gray-white matter resolution is very sensitive in detecting subtle demyelination, the sensitivity being still further enhanced by FLAIR sequences. The present study concludes that MRI, in correlation with the clinical signs and symptoms is an ideal modality in early diagnosis of white matter diseases and aids in the early institution of therapy so that the curable conditions among them can be treated.

Purpose: To evaluate the safety and short-term efficacy of uterine artery embolization (UAE) in treating uncontrolled vaginal bleeding in a group of gynecologic and obstetric patients. Methods: Eighteen symptomatic patients were treated by this method. These included 11 patients with an advanced carcinoma of the cervix, three patients with uterine fibroid, three patients with a uterine arterio-venous malformation (AVM) and one patient with placenta accreta. All procedures were done by transfemoral route. Polyvinyl alcohol foam particles, 300-500 microns in size, were used for embolization. Imaging by duplex sonography was performed before the procedure and at one week and one-month follow-up. Result: Eight patient (six with carcinoma of the cervix and one each with a uterine AVM and placenta accreta) underwent unilateral and 10 patients underwent a bilateral UAE. All procedures were technically and clinically successful. Four patients developed a self-limiting post-embolization syndrome, characterized by mild fever and leucocytosis. They responded well to analgesic therapy. One patient developed a groin hematoma that resolved with conservative management. All patients reported mild to moderate pelvic pain in the post-embolization period which lasted for 24-72 hours and responded well to medication. There were no permanent sequelae of UAE. The follow-up period was 2-17 months (mean, 7 months). During follow-up, vaginal bleeding was controlled in all of them. It stopped completely in 8 and was significantly reduced in 10 patients. The size of the tumor regressed in all patients. The AVM was completely blocked in one and showed a substantially reduced flow in two patients. Conclusion: UAE is used in treating vaginal bleeding, irrespective of its etiology. The procedure is safe, produces no permanent sequelae and provides an effective control of hemorrhage. The overall complication rate is low.

Scleroma of the larynx without involvement of the upper respiratory tract is a rare clinical entity. We present a case of isolated laryngeal scleroma with unusual computed tomography findings of a cystic lesion involving the left pyriform sinus.