Manchester Royal Infirmary, Manchester, UK British Nuclear Medicine Society Oral and Poster Abstracts 2007

Pandit, M.M.; Prescott, M.C.; Lawson, R.S.; James, J.M.; Arumugam, P. Author Information

Hamilton, N.V.; Ellul, G.J.; Al-Bahrani, G.I.; James, J.M.; Prescott, M.C.; Parrott, N.R. Author Information

Pulmonary embolism remains a major cause of morbidity and mortality, being responsible for an estimated 200,000 deaths per annum in the USA and 21,000 per annum in the UK. Lung scintigraphy is in many instances the investigation of choice in suspected pulmonary thromboembolism. A normal perfusion lung scan excludes pulmonary embolism. An abnormal perfusion scan, while being sensitive, is of low specificity for the diagnosis of pulmonary embolism and needs to be complemented with a ventilation study. Lung ventilation has been studied using inert gases of radiolabelled aerosols. The new radiopharmaceutical Tc-99(m)-Technegas is a suspension of (9)9Tc(m)-labelled, ultrafine, carbon particles produced in an atmosphere of high-purity argon. The size of the particles is of the order of 0.00-0.2 mu m, which assures good peripheral penetration and alveolar deposition. After inhalation, static images in multiple projections may be acquired. The resultant images are of excellent technical quality and several publications have shown the value of Technegas images as an adjunct to perfusion imaging in suspected pulmonary thromboembolism. Studies comparing Technegas images with other ventilatory radiopharmaceuticals have in the majority of instances reported comparable diagnostic qualities.

Technegas and Pertechnegas are radioactive aerosols produced in a commercial generator and used for lung scintigraphy. The aerosols are produced by first evaporating to dryness standard technetium-99m generator eluate (99m-TcO4 in normal saline) in a graphite crucible (thesimmer stage) and then heating this to 2500° C (the „burn” stage). The aim of this work was to measure the particle size distributions of these agents and relate this to regional lung deposition. Factors that may vary during production of the aerosol in routine use were investigated to determine whether they influenced the particle size. Activity size distributions were measured using a serial wire-screen diffusion battery. The Technegas size distribution was approximately log-normal with an activity median diameter of 158 nm and a geometric standard deviation of 1.5. The results for Pertechnegas were similar. The median size increased with the number of simmers and with the time from generation. The increase in size with the number of simmers is thought to be due to the increased salt content in the crucible prior to the „burn”. The predicted lung deposition is 37% in the alveolar region and 5% in the bronchial region. Significant changes in deposition are not predicted over the range of particle sizes measured.

Technegas lung ventilation images sometimes have 'hot spots', particularly in patients with respiratory disease. A novel technique is presented for quantifying this 'spottiness' using morphological texture analysis. A set of 32 images from patients with various respiratory diseases is studied. Images are filtered at a range of scales using morphological opening, and the slopes of image metrics versus structuring element size are used as texture parameters. The results are compared with the opinions of three experienced nuclear medicine physicians who have classified the images into two groups, 'spotty' and 'non-spotty', and have ranked the former. For the spotty images, the computer and observer ranks are compared; the highest correlation is rs = 0.66 (p = 0.01) for a single parameter, and rs = 0.71 (p < 0.01) for a combination of two parameters. Using a pair of parameters, 83% and 90% correct classification rates are obtained for the spotty and non-spotty classes, respectively. It is concluded that these texture parameters provide a useful measure of image spottiness, and it is demonstrated that this technique is superior to previously published methods. The practical value of the technique is illustrated using two applications.

The aim of this work was to investigate the influence of inhalation technique on Technegas image quality and on fractional particle deposition. This was investigated in six normal volunteers using three different types of breathing pattern. Fractional deposition was determined by analysis of dynamic gamma camera images acquired during Technegas administration. Static lung images were subsequently acquired and assessed independently by three experienced observers. High-quality images were obtained in all cases although slight differences were noted. The images produced using a slow deep inspiration with a breath hold (i.e. the standard method) were of more uniform texture and also had the least gradient in activity from apex to base. The converse was true for a rapid inhalation technique. The average fractional deposition per breath was 55%, but this varied between individuals and with breathing pattern, being most influenced by the total duration of a breath. We conclude that for patient studies the standard inhalation technique is best, although variation to suit individual patients would be acceptable. These results contrast with similar studies using conventional radio-aerosols, which tend to show a greater sensitivity of image appearance to changes in breathing pattern and lower fractional depositions.

s of the British Nuclear Medicine Society Autumn Meeting: MANCHESTER, 6-7 OCTOBER 1994: SESSION 1: HEART AND LUNG: PDF Only

s of the British Nuclear Medicine Society Autumn Meeting: MANCHESTER, 6-7 OCTOBER 1994: SESSION 1: HEART AND LUNG: PDF Only

s of the British Nuclear Medicine Society Autumn Meeting: MANCHESTER, 6-7 OCTOBER 1994: SESSION 1: HEART AND LUNG: PDF Only

In terms of future morbidity and mortality, one of the most important considerations in urinary tract infection is the age of the patient. In adults, only those with complications or illnesses that fail to respond to treatment require investigation to exclude underlying pathology. In contrast, the young are at risk of future hypertensive and renal disease; imaging techniques are therefore of paramount importance to identify those with renal parenchymal disease at an early stage and permit appropriate and adequate treatment. 99mTc-dimercaptosuccinic acid scintigraphy is emerging as the method of choice for this purpose, because it combines high specificity and sensitivity with convenience, repeatability, and acceptable radiation doses. Voiding cystourethrography will also be required in many cases to exclude bladder pathology. New developments include the use of color Doppler ultrasonography and the nuclear magnetic resonance technique of rapid acquisition recall echo urography, both of which may become of value for the detection of scarring

The aim of this work was to assess the levels of airborne activity and contamination arising from Technegas ventilation scintigraphy and to estimate doses to staff. The maximum air concentration was below the 99Tcm-derived air concentration limit and considerably lower than reported levels for conventional radioaerosols. The level of contamination on staff gloves and aprons exceeded the body surface contamination limit in 63 and 9% of cases, respectively. Levels of contamination and air concentration were generally higher if the patient had difficulty with the administration procedure. Room surface contamination was very low. In 24% of cases activity was detectable on staff (either in the hair or nose) using gamma camera imaging. Annual skin doses from these sources are calculated to be below the limit for deterministic effects. Whole body effective doses are calculated to be similar to those received by staff performing other nuclear medicine studies. However, care should be exercised to keep exposure from both airborne and fixed sources to a minimum and a regular review of contamination levels is recommended. We recommend the wearing of gloves for all Technegas administrations and disposable hats and masks may be considered in certain cases.