Guidance on prevention of unintended and accidental radiation exposures in nuclear medicine

Nuclear medicine (NM) procedures for diagnosis and treatment of disease are performed routinely in hospitals throughout the world. These involve preparation and administration to patients of pharmaceuticals labelled with radioactive material. The International Atomic Energy Agency (IAEA) and the World Health Organisation highlighted the need for improvement in prevention of medical radiation incidents and accidents in the Bonn Call-for-Action in 2012. An IAEA Technical Meeting was held on prevention of unintended exposures and accidents in NM in 2018 to address the issue. Exposures can take place at any time when radioactive material is being produced and used, and the risk continues after procedures have been completed. Thus there is potential for staff or members of the general public to be exposed, as well as patients. This paper sets out guidelines for incident prevention based on presentations and discussions at the meeting, and review of reports from the literature. It deals with potential incidents in in-house radionuclide production, radiopharmaceutical preparation, administration to patients, and following a procedure, as well as aspects in management of radioactive materials. Special attention has been paid to therapeutic procedures, as these have the potential to cause more harm to patients from erroneous administrations, including tissue reactions from extravasation of radiopharmaceutical, and could lead to significant contamination events. Administration of NM therapy is generally contraindicated in pregnancy. Identification of any patient who may be pregnant is crucial and it might be necessary to verify this with a pregnancy test for patients within the age band considered to be fertile. Inclusion of NM therapy incidents in the IAEA automated reporting system SAFRON is recommended. In summary, the paper aims to highlight errors that could occur during different phases of NM procedures in order to aid prevention of incidents. The value of periodic audit in evaluating systems in place on a regular basis is emphasised. Approaches to incident investigation and follow-up are described, and the need to ensure corrective action is taken to address any deficiencies stressed.

Spatial variations in trace element concentrations of the sea urchin, Paracentrotus lividus, a first reference study in the Mediterranean Sea

A study on Trace Elements (TE) from sea urchin gonads has been conducted in the western Mediterranean Sea. Contamination data were used to determine a Trace Method Pollution Index (TEPI). TE concentrations varied considerably depending on the location of the sampling stations. The results showed that five trace elements (Zn, Fe, As, Al, Cu) are ubiquitous. The geographical area considered (Corsica) represents an important range of environmental conditions and types of pressure that can be found in the western Mediterranean Sea. TEPI was used to classify the studied sites according to their degree of contamination and allowed reliable comparison of TE contamination between local and international sites. TE contamination of the western Mediterranean Sea displayed a north-to-south gradient, from the Italian coasts down through the insular Corsican coasts to the north African littoral. Due to the increasing environmental pressure on the Mediterranean Sea, a regular monitoring of TE levels in marine organisms is necessary to prevent any further environmental deterioration.

Trace element concentrations in the apex predator swordfish (Xiphias gladius) from a Mediterranean fishery and risk assessment for consumers

Swordfish (Xiphias gladius L., 1758) is an apex predator, highly migratory meso-pelagic fish widely distributed in the Atlantic Ocean and Mediterranean. As top predators, this fish may be the end reservoir of the bioaccumulation of trace elements in a food chain because they occupy higher trophic levels and are an important food source, causing them to be potentially hazardous to consume. This study aims to investigate the concentration of 18 trace elements of Swordfish, caught in the Mediterranean Sea and to discuss human exposure risks. The mean element levels in the fish muscles were clearly below the maximum allowable concentrations established by International food safety regulations. The data suggested that the risk is minor and acceptable for human health. The findings of this study amplify the scarce database on contaminants available, especially new data on "emerging elements", for this species from the Mediterranean Sea.

Comparison of otolith and scale readings for age and growth estimation of common dentex Dentex dentex

Three methods of age estimation were compared for Dentex dentex. Based on sectioned otoliths, scales appeared to be relevant only up to 5 years and whole otoliths up to 12 years. The maximum estimated age was 36 years, which constitutes to date the oldest age reported.

Monte Carlo modeling provides accurate calibration factors for radionuclide activity meters

Accurate determination of calibration factors for radionuclide activity meters is crucial for quantitative studies and in the optimization step of radiation protection, as these detectors are widespread in radiopharmacy and nuclear medicine facilities. In this work we developed the Monte Carlo model of a widely used activity meter, using the Geant4 simulation toolkit. More precisely the "PENELOPE" EM physics models were employed. The model was validated by means of several certified sources, traceable to primary activity standards, and other sources locally standardized with spectrometry measurements, plus other experimental tests. Great care was taken in order to accurately reproduce the geometrical details of the gas chamber and the activity sources, each of which is different in shape and enclosed in a unique container. Both relative calibration factors and ionization current obtained with simulations were compared against experimental measurements; further tests were carried out, such as the comparison of the relative response of the chamber for a source placed at different positions. The results showed a satisfactory level of accuracy in the energy range of interest, with the discrepancies lower than 4% for all the tested parameters. This shows that an accurate Monte Carlo modeling of this type of detector is feasible using the low-energy physics models embedded in Geant4. The obtained Monte Carlo model establishes a powerful tool for first instance determination of new calibration factors for non-standard radionuclides, for custom containers, when a reference source is not available. Moreover, the model provides an experimental setup for further research and optimization with regards to materials and geometrical details of the measuring setup, such as the ionization chamber itself or the containers configuration.

Radiation dose around a PET scanner installation: comparison of Monte Carlo simulations, analytical calculations and experimental results

PURPOSE

Monte Carlo study of radiation transmission around areas surrounding a PET room.

METHODS

An extended population of patients administered with (18)F-FDG for PET-CT investigations was studied, collecting air kerma rate and gamma ray spectra measurements at a reference distance. An MC model of the diagnostic room was developed, including the scanner and walls with variable material and thickness. MC simulations were carried out with the widely used code GEANT4.

RESULTS

The model was validated by comparing simulated radiation dose values and gamma ray spectra produced by a volumetric source with experimental measurements; ambient doses in the surrounding areas were assessed for different combinations of wall materials and shielding and compared with analytical calculations, based on the AAPM Report 108. In the range 1.5-3.0 times of the product between the linear attenuation coefficient and thickness of an absorber (μ x), it was observed that the effectiveness of different combinations of shielding is roughly equivalent. An extensive tabulation of results is given in the text.

CONCLUSIONS

The validation tests performed showed a satisfactory agreement between the simulated and expected results. The simulated dose rates incident on, and transmitted by the walls in our model of PET scanner room, are generally in good agreement with analytical estimates performed using the AAPM Publication No. 108 method. This provides an independent confirmation of AAPM's approach. Even in this specific field of application, GEANT4 proved to be a relevant and accurate tool for dosimetry estimates, shielding evaluation and for general radiation protection use.

Drop rebound after impact: the role of the receding contact angle

Data from the literature suggest that the rebound of a drop from a surface can be achieved when the wettability is low, i.e., when contact angles, measured at the triple line (solid-liquid-air), are high. However, no clear criterion exists to predict when a drop will rebound from a surface and which is the key wetting parameter to govern drop rebound (e.g., the "equilibrium" contact angle, θeq, the advancing and the receding contact angles, θA and θR, respectively, the contact angle hysteresis, Δθ, or any combination of these parameters). To clarify the conditions for drop rebound, we conducted experimental tests on different dry solid surfaces with variable wettability, from hydrophobic to superhydrophobic surfaces, with advancing contact angles 108° < θA < 169° and receding contact angles 89° < θR < 161°. It was found that the receding contact angle is the key wetting parameter that influences drop rebound, along with surface hydrophobicity: for the investigated impact conditions (drop diameter 2.4 < D0 < 2.6 mm, impact speed 0.8 < V < 4.1 m/s, Weber number 25 < We < 585), rebound was observed only on surfaces with receding contact angles higher than 100°. Also, the drop rebound time decreased by increasing the receding contact angle. It was also shown that in general care must be taken when using statically defined wetting parameters (such as advancing and receding contact angles) to predict the dynamic behavior of a liquid on a solid surface because the dynamics of the phenomenon may affect surface wetting close to the impact point (e.g., as a result of the transition from the Cassie-Baxter to Wenzel state in the case of the so-called superhydrophobic surfaces) and thus affect the drop rebound.

Water drops dancing on ice: how sublimation leads to drop rebound

Drop rebound is a spectacular event that appears after impact on hydrophobic or superhydrophobic surfaces but can also be induced through the so-called Leidenfrost effect. Here we demonstrate that drop rebound can also originate from another physical phenomenon, the solid substrate sublimation. Through drop impact experiments on a superhydrophobic surface, a hot plate, and solid carbon dioxide (commonly known as dry ice), we compare drop rebound based on three different physical mechanisms, which apparently share nothing in common (superhydrophobicity, evaporation, and sublimation), but lead to the same rebound phenomenon in an extremely wide temperature range, from 300 °C down to even below -79 °C. The formation and unprecedented visualization of an air vortex ring around an impacting drop are also reported.

Optical imaging of radioisotopes: a novel multimodal approach to molecular imaging

In this review there will be presented an overview of the literature about the recent developments on radiotracers imaging using optical methods and their applications. We will begin with a short summary regarding the discovery of Cerenkov radiation (CR) and then focus on the early developments and experimental validation of planar Cerenkov luminescence imaging. A significant improvement in Cerenkov luminescence imaging was given by the development of tomographic methods in order to obtain in vivo whole body 3D images of Cerenkov sources. An interesting and original application discussed in this review is the use of CR as the excitation source of quantum dots and fluorophores. We will also present some recent experimental results on in vivo radio luminescence imaging of alpha and gamma emitters. All these results make optical radioisotopes imaging an interesting cost-effective tool for the screening of new probes for both imaging and therapeutic applications. Other interesting aspects are the uses of Cerenkov radiation for radiotherapy and for radiopharmaceuticals synthesis applications. We will conclude by summarising the most important results and the future challenges.

Influence of the wettability on the boiling onset

Experimental investigation of pool boiling is conducted in stationary conditions over very smooth bronze surfaces covered by a very thin layer of gold presenting various surface treatments to isolate the role of wettability. We show that even with surfaces presenting mean roughness amplitudes below 10 nm the role of surface topography is of importance. The study shows also that wettability alone can trigger the boiling and that the boiling position on the surface can be controlled by chemical grafting using for instance alkanethiol. Moreover, boiling curves, that is, heat flux versus the surface superheat (which is the difference between the solid surface temperature and the liquid saturation temperature), are recorded and enabled to quantify, for this case, the significant reduction of the superheat at the onset of incipient boiling due to wettability.

Some experimental studies on 89Zr production

The radionuclide 89Zr (T 1/2=78.4ߙh) is particularly attractive for in vivo assessment of biochemical proesses characterized by biological half times in the order of several hours. In the present study we assessed the feasibility of 89Zr production via the 89Y(p,n)89Zr reaction. Irradiation tests were performed using a 16.5ߙMeV GE-PETtrace cyclotron. High purity (>99.9%) yttrium metallic foils (0.15ߙmm) were irradiated in a solid target station developed in our Institution. The literature cross section data of all the nuclear reactions possible in the energy range of interest were carefully studied to optimize the irradiation parameters. The irradiated target was dissolved in 1ߙN HCl and the activity of the sample was measured in a CRC-15 PET dose calibrator, setting different values for the calibration factor. The sample activity was then measured usin g a calibrated HPGe gamma ray detector. A comparison of the activity measurements allowed the evaluation of the calibration factor for the Capintec CRC-15 PET; for a 3ߙml syringe geometry, it was found 739±60. Saturation yields of 89Zr were found to be 1150±110ߙMBq/μA for a single 0.15ߙmm thick disc irradiation (E p=12.6→11.2ߙMeV) and 2400±220ߙMBq/μA for irradiation of two discs of total thickness 0.3ߙmm (E p=12.6→9.5MeV). Total produced activities in the range of 200–400ߙMBq (according to target thickness) were repeatedly and safely obtained by 60ߙmin bombardments at 20ߙμA. Analysis of gamma ray spectra of all the samples showed a very high radionuclidic purity (>99.9995%).

Prediction of (89)Zr production using the Monte Carlo code FLUKA

The widely used Monte Carlo simulation code FLUKA has been utilized to prototype a solid target for the production of (89)Zr by irradiation of a metallic (89)Y target foil in a 16.5MeV proton biomedical cyclotron, through the reaction (89)Y(p, n)(89)Zr. Simulations were performed with and without an Al energy degrader. In the setup of the geometry of the target, state of the art support tools, like SimpleGeo, were used for accurate, detailed modeling. The results permitted a quick assessment of all possible radionuclidic contaminants and confirmed that the use of an energy degrader avoids production of the most important impurity, (88)Zr. The estimated value for the activity produced in one hour of irradiation at 20μA is 384 ± 42MBq; this is encouraging, indicating possible production of clinically significant amounts of activity with the relatively simple target setup adopted. Initial experimental tests gave results in excellent agreement with simulations, confirming the usefulness and accuracy of FLUKA as a tool for the design and optimization of targets for the production of PET radionuclides.

An innovative method to control the incipient flow boiling through grafted surfaces with chemical patterns

The onset of flow boiling of a liquid is linked to the superheat condition that is necessary to activate the nucleation sites on contacting surfaces. The nucleation sites are usually represented by cavities in the rough surface of the heat exchanger. On smooth surfaces, the region where bubble detachment does not occur due to the lack of superheating may constitute a serious limitation for microfluidic devices. This paper shows the first experimental evidence that the position of the active nucleation sites can be controlled through chemical patterning of smooth surfaces: in this study, the heated surfaces are chemically grafted with alkylsilane self-assembled monolayers by microcontact printing. The analysis of the propagation of the bubble zone area quantitatively shows that the bubbles remain localized on top of the grafted zone and that, in the initial phase of the experiment, the center of mass of the bubble zone only moves along the vertical axis, without lateral drift.

General methodology for evaluating the adhesion force of drops and bubbles on solid surfaces

The shortcomings of the current formulation for calculating the adhesion force for drops and bubbles with noncircular contact lines are discussed. A general formulation to evaluate the adhesion force due to surface forces is presented. Also, a novel methodology, that is, IBAFA, image based adhesion force analysis, was developed to allow implementation of the general formulation. IBAFA is based on the use of multiple profile images of a drop. The images are analyzed (1) to accurately reconstruct the contact line shape, which is analytically represented by a Fourier cosine series, and (2) to measure contact angles at multiple locations along the contact line and determine the contact angle distribution based on a linear piecewise interpolation routine. The contact line shape reconstruction procedure was validated with both actual experiments and simulated experiments. The procedure for the evaluation of the adhesion force was tested using simulated experiments with synthetic drops of known shapes. A comparison with current methods showed that simplifying assumptions (e.g., elliptical contact line or linear contact angle distribution) used in these methods result in errors up to 76% in the estimated adhesion force. However, the drop adhesion force evaluated using IBAFA results in small errors on the order of 1%.

Radiolabelling, quality control and radiochemical purity assessment of the Octreotide analogue 68Ga DOTA NOC

Somatostatin receptors 1-5 are over expressed in neuroendocrine tumours (NETs). 68Ga-labelled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-Nal3-Octreotide (DOTA NOC), a recent synthesized somatostatin analogue, shows high affinity for those receptors. Herein, modifications of a commercial module for the labelling of DOTA NOC with 68Ga, as well as the assessment of time course of the radiochemical purity variation are described. The evaluation of radiochemical stability was done by two different chromatographic methods: reversed-phase radio HPLC and fast TLC analysis. Labelled compound has been found radiochemically stable within 3h from the end of labelling (EOL) and radiochemical purity was always higher than 99%. After 73 labelling sessions the system showed great reproducibility and high radiochemical yield.

Risk management of renal biopsy: 1387 cases over 30 years in a single centre

BACKGROUND

Although renal biopsy is largely employed, even in old patients with systemic diseases, few clinical studies have addressed its risk management. We aimed to obtain a comprehensive assessment of safety/utility ratio of percutaneous renal biopsy.

PATIENTS AND METHODS

Retrospective review of all the 1387 patients who consecutively underwent renal biopsy in a single centre over three decades (1973-2002) was made, with calculation of complications, multivariate logistical analyses to evaluate risk factors of complications, and rate of alteration of clinical hypotheses by pathological diagnosis.

RESULTS

There were no deaths and five major complications, (0.36%). One nephrectomy (0.07%), two surgical revisions (0.1%) and two arterial-venous fistulae (0.1%). There were also 337 minor bleeding complications (24.2%) (16.4% gross haematuria and 7.8% clinically relevant haematomas needing at least prolonged bed rest). Multivariate analyses demonstrated that the risk for complications was significantly increased by systemic autoimmune diseases with odds ratio (OR) 2.06, 95% confidence interval (CI)=1.40-3.01, end-stage kidney/acute-tubular necrosis (OR 2.96, 95% CI=1.19-7.30), and prolonged bleeding time test (BTT) (OR 1.87, 95% CI=1.17-2.83). Among the 1288 cases in which a clinical hypothesis before renal biopsy was recorded, renal pathology changed previous diagnoses in 423/1,288 (32.8%) of cases.

CONCLUSIONS

Risk assessment demonstrates that renal biopsy is a useful procedure with a low incidence of serious complications. Platelet function is the only modifiable factor significantly related to bleeding complications, suggesting the need for a more standardized alternative to the BTT. Platelet function should be evaluated to select low-risk patients for renal biopsy as 'a day case procedure', in order to build adequate risk management strategies.

68Ga-DOTANOC: biodistribution and dosimetry in patients affected by neuroendocrine tumors

OBJECTIVES

The aim of this work was the evaluation of biodistribution and radiation dosimetry of (68)Ga-DOTANOC in patients affected by neuroendocrine tumors.

MATERIALS AND METHODS

We enrolled nine patients (six male and three female) affected by different types of neuroendocrine tumors (NETs). Each patient underwent four whole body positron emission tomography (PET) scans, respectively, at 5, 20, 60, and 120 min after the intravenous injection of about 185 MBq of (68)Ga-DOTANOC. Blood and urine samples were taken at different time points post injection: respectively, at about 5, 18, 40, 60, and 120 min for blood and every 40-50 min from injection time up to 4 h for urine. The organs involved in the dosimetric evaluations were liver, heart, spleen, kidneys, lungs, pituitary gland, and urinary bladder. Dosimetric evaluations were done using the OLINDA/EXM 1.0 software.

RESULTS

A physiological uptake of (68)Ga-DOTANOC was seen in all patients in the pituitary gland, the spleen, the liver, and the urinary tract (kidneys and urinary bladder). Organs with the highest absorbed doses were kidneys (9.0E-02+/-3.2E-02mSv/MBq). The mean effective dose equivalent (EDE) was 2.5E-02+/-4.6E-03 mSv/MBq.

DISCUSSION AND CONCLUSIONS

The excretion of the compound was principally via urine, giving dose to the kidney and the urinary bladder wall. As SSTR2 is the most frequently expressed somatostatin receptor and (68)Ga-DOTANOC has high affinity to it, this compound might play an important role in PET oncology in the future. The dosimetric evaluation carried out by our team demonstrated that (68)Ga-DOTANOC delivers a dose to organs comparable to, and even lower than, analogous diagnostic compounds.

Artefacts of PET/CT images

Positron emission tomography (PET) is a non-invasive imaging modality, which is clinically widely used both for diagnosis and accessing therapy response in oncology, cardiology and neurology.Fusing PET and CT images in a single dataset would be useful for physicians who could read the functional and the anatomical aspects of a disease in a single shot.The use of fusion software has been replaced in the last few years by integrated PET/CT systems, which combine a PET and a CT scanner in the same gantry. CT images have the double function to correct PET images for attenuation and can fuse with PET for a better visualization and localization of lesions. The use of CT for attenuation correction yields several advantages in terms of accuracy and patient comfort, but can also introduce several artefacts on PET-corrected images.PET/CT image artefacts are due primarily to metallic implants, respiratory motion, use of contrast media and image truncation. This paper reviews different types artefacts and their correction methods.PET/CT improves image quality and image accuracy. However, to avoid possible pitfalls the simultaneous display of both Computed Tomography Attenuation Corrected (CTAC) and non corrected PET images, side by side with CT images is strongly recommended.

Quality control of 99Mo/99Tcm generators: results of a survey of the Radiopharmacy Working Group of the Italian Association of Nuclear Medicine (AIMN)

A multicentre survey of the quality control of 99Tcm generators has been completed: 245 generators from seven different commercial sources were tested over a period of 2 years. The results indicate that the mean pH of the eluates was 5.8 +/- 0.6; the aluminium contents were typically < 10 ppm; the radiochemical purity was 99.8 +/- 0.4% and the median 99Mo content was 3.8 x 10(-4) percent. The elution profiles gave a volume of 1.9 ml to obtain 50% of the total eluted activity and of 4.9 ml to obtain 95%. Other radionuclide impurities and heavy metal breakthrough were evaluated by graphite furnace absorption spectrometry and inductively coupled plasma mass spectrometry. National guidelines for the standardization of radiopharmacy procedures are currently being compiled.

Reproducibility of a solid and of a liquid caloric meal for gastric emptying studies

Simple meals are required for routine scintigraphic gastric emptying studies. We evaluated the reproducibility of a caloric liquid meal (520 kcal) compared to that of a solid meal (638 kcal) in 8 and 11 healthy volunteers, respectively. Gastric emptying rates and half-times were similar in two tests using the same meal, while the methods used to express lag times were not highly reproducible. The emptying rates and half-times of the liquid meal were delayed after the intake of bellafoline. In conclusion, this study demonstrates that: (a) gastric emptying rates and half-times are reproducible parameters for the expression of scintigraphic gastric emptying studies; (b) mathematical methods to express lag times are not highly reproducible; (c) a 500 kcal liquid meal is sensitive to the effects of bellafoline, a drug able to delay gastric emptying. Further clinical evaluation is required to test its applicability in routine studies.

Reproducibility of a solid and of a liquid caloric meal for gastric emptying studies

Simple meals are required for routine scintigraphic gastric emptying studies. We evaluated the reproducibility of a caloric liquid meal (520 kcal) compared to that of a solid meal (638 kcal) in 8 and 11 healthy volunteers, respectively. Gastric emptying rates and half-times were similar in two tests using the same meal, while the methods used to express lag times were not highly reproducible. The emptying rates and half-times of the liquid meal were delayed after the intake of bellafoline. In conclusion, this study demonstrates that: (a) gastric emptying rates and half-times are reproducible parameters for the expression of scintigraphic gastric emptying studies; (b) mathematical methods to express lag times are not highly reproducible; (c) a 500 kcal liquid meal is sensitive to the effects of bellafoline, a drug able to delay gastric emptying. Further clinical evaluation is required to test its applicability in routine studies.

Risk indicators of delayed gastric emptying of solids in patients with functional dyspepsia

BACKGROUND & AIMS

Although gastric dysmotility and dyspeptic symptoms are often associated, their relationship remains unclear. The aim of this study was to evaluate the relationship between gastric emptying abnormalities and clinical features in functional dyspepsia.

METHODS

In 343 patients with functional dyspepsia, the gastric emptying of solids was measured by a radioisotopic technique and four dyspeptic symptoms (epigastric pain and burning, postprandial fullness, nausea, and vomiting) were measured as absent, mild, relevant, and severe, according to their influence on patients' usual activities.

RESULTS

Delayed gastric emptying was detected in 33.5% of dyspeptics. Delayed gastric emptying was particularly frequent in patients characterized by female sex, low body weight, presence of relevant and severe postprandial fullness, nausea, vomiting, and absence of relevant and severe epigastric pain. Logistic regression showed that delayed gastric emptying was invariably associated with female sex and postprandial fullness (odds ratio, 2.34; 95% confidence interval, 1.45-3.75) and vomiting (odds ratio, 4.04; 95% confidence interval, 1.30-12.54) when coded as severe and only postprandial fullness (odds ratio, 3.78; 95% confidence interval, 1.78-8.01) when coded as relevant and severe.

CONCLUSIONS

Female sex, relevant and severe postprandial fullness, and severe vomiting are independently associated with delayed gastric emptying of solids in patients with functional dyspepsia seen in a referral center.

Evaluation of lung clearance of inhaled pertechnegas

Pertechnegas is a new ventilation agent produced by modifying the atmosphere of combustion of Technegas. Due to its rapid disappearance from the lungs, Pertechnegas has been suggested as useful in measuring pulmonary epithelial permeability. This study aimed to assess the reliability of ventilation scans with Pertechnegas to evaluate alveolar-capillary permeability. Six non-smokers with no evidence of pulmonary disease were investigated. Scintigraphic data were used to evaluate the site of Pertechnegas deposition (by assessing the Penetration Index [PI] of the gas), its clearance rate (by calculating the time to half-clearance [T1/2]) and its lung distribution (by means of a pixel-by-pixel analysis. PI measurements produced a mean value of 88.8 +/- 13.3% (range 69-117%). Time activity curves showed a fast clearance in all cases (mean T1/2 = 10.7 +/- 2.1 min, range 8.1-14.3 min). Comparison of statistical indices of uniform deposition (skewness and kurtosis) indicated satisfactory homogeneity of Pertechnegas distribution throughout the lungs. These data show that after inhalation Pertechnegas has a peripheral deposition and a homogeneous distribution in the lungs and is rapidly cleared through the alveolar-capillary barrier. In conclusion Pertechnegas can be recommended as a potential radiopharmaceutical for studying the pulmonary epithelial barrier.

Early pulmonary involvement in systemic sclerosis assessed by technetium-99m-DTPA clearance rate

Systemic sclerosis (SS) is frequently associated with interstitial lung disease, but clinical symptoms and radiologic abnormalities may occur late in the course of the disease. This study investigated early pulmonary involvement by assessing the clearance rate of inhaled 99mTc-diethylenetriaminepentaacetic acid (DTPA).

METHODS

Sixteen patients with proved SS, no clinical pulmonary symptoms and normal chest radiogram were prospectively studied. The 99mTc-DTPA clearance rate was calculated as the time to half clearance (T1/2) and compared with values obtained in healthy nonsmokers.

RESULTS

Six patients showed abnormally increased clearance (T1/2 < 53 min). Rapid clearance was not correlated to SS disease duration or to abnormal pulmonary function tests. Five of six patients with abnormally increased clearance underwent high-resolution CT, which in all five demonstrated pathologic findings that were suggestive of early interstitial disease.

CONCLUSION

These findings indicate that in SS asymptomatic patients may frequently present with abnormal 99mTc-DTPA clearance; 99mTc-DTPA lung scintigraphy may allow early detection of subclinical pulmonary involvement in SS.

Evaluation of hypertensive patients with a solitary kidney using captopril renal scintigraphy with 99Tcm-MAG3

The study aimed to evaluate the safety and reliability of captopril renal scintigraphy (CRS) for diagnosing functionally significant renal artery stenosis (RAS) in hypertensive patients with a solitary kidney. Radionuclide studies were carried out using 100 MBq 99Tcm-mercaptoacetyl triglycine (MAG3), 1 h after administration of 50 mg captopril, and repeated in baseline condition when abnormalities were observed in the provocative study. Scintigraphic diagnosis of RAS was based on analysis of captopril-induced changes of the radiorenographs. Overall, 12 patients with a solitary kidney were investigated, and scintigraphic results compared to angiographic findings. All five patients with positive CRS showed an RAS > 50%, whereas only one of the seven patients with negative CRS was affected by RAS. A significant fall in mean arterial pressure was recorded after captopril administration (123 +/- 12 mm Hg before versus 108 +/- 11 after), but no serious side effects were observed. Our results demonstrate that captopril-induced modifications of the renogram could effectively be used to diagnose the presence of RAS. Captopril renal scintigraphy may therefore be suggested as a reliable and safe noninvasive approach to evaluate hypertensive patients with a solitary kidney.

A comparison of rest sestamibi and rest-redistribution thallium single photon emission tomography: possible implications for myocardial viability detection in infarcted patients

Thirty patients (26 men, 4 women, mean age 61 +/- 8 years) who had suffered myocardial infarction 15 +/- 6 months previously, were submitted to (1) standard stress-redistribution thallium-201 single photon emission tomography (SPET), (2) rest-redistribution 201T1 SPET and (3) stress-rest technetium-99m sestamibi SPET. Uptake modifications in relation to exercise-induced defects were evaluated in a total of 390 myocardial segments. Tracer uptake was scored as normal (=0), mildly reduced (=1), apparently reduced (=2), severely reduced (=3) or absent (=4). Comparison of stress studies failed to show any statistical difference (58% segmental abnormalities with sestamibi vs 61% with thallium). Uptake abnormalities (score 1-4) were detected in 55% of the segments with sestamibi, 55% with standard thallium redistribution, 55% with early imaging after thallium injection at rest and 54% with 3-h delayed rest imaging (P = NS). Absence of tracer uptake (score = 4) under resting conditions was recorded in 75 (19%) segments with standard 201T1 redistribution, 75 (19%) with rest sestamibi, 70 (18%) with rest 201T1 imaging and 62 (16%) with rst-redistribuion 201T1 (P < 0.05 vs other imaging modalities). Thus, 3-h delayed rest thallium imaging detected reversibility of uptake defects in a significantly higher number of myocardial segments. This finding might have important implications for both tracer and technique selection when myocardial viability is the main clinical issue.

The effect of different dosage schedules of cisapride on gastric emptying in idiopathic gastroparesis

The aim of this study was to determine the optimal dosage regimen of cisapride for the treatment of idiopathic gastroparesis. We studied 17 patients with documented idiopathic gastroparesis in a three-way, cross-over, double-blind study with three 4-day treatment periods separated by at least 3 days without treatment. In each period, the patients were preloaded with cisapride (10 mg tid) for three days. On the fourth day (the test day) they took either 10 mg or 20 mg before breakfast and placebo before lunch (1 x 10 mg), (1 x 20 mg), or 10 mg before breakfast and 10 mg before lunch (2 x 10 mg). The medications were taken 30 min before meals. Gastric emptying of solids (99mTc-sulphur colloid) was measured at lunch time under basal conditions and during each treatment period. Plasma concentrations of cisapride were determined before the breakfast dose, before the lunch dose, and at 1, 2, 3, 4 and 5 h after. The greatest acceleration in gastric emptying occurred with the 2 x 10 mg regimen. Although the single morning dose of 20 mg also significantly accelerated gastric emptying (P = 0.05), the reduction was not as substantial. Plasma concentrations of cisapride were significantly higher after 2 x 10 mg than after 1 x 20 mg or 1 x 10 mg. There was a significant relation between cisapride plasma concentrations and changes in gastric emptying. Peak concentrations of cisapride greater than 60 ng.ml-1 were invariably associated with acceleration of gastric emptying. We conclude that cisapride 10 mg tid before meals is the optimal dose for the treatment of idiopathic gastroparesis.

Prognostic value of captopril renal scintigraphy in renovascular hypertension

This study evaluates the prognostic value of captopril renal scintigraphy in hypertensive patients undergoing renal artery revascularization. Preoperative studies of 51 patients were correlated with blood pressure results at 6- and 12-mo follow-up. Captopril-renal scintigraphy was carried out 1 hr after oral administration of 50 mg of captopril, using either 220 MBq of 99mTc-DTPA or 74 MBq of 99mTc-MAG3, followed by a baseline study in case of abnormal results. Evidence of amelioration or normalization in relation to captopril study was considered predictive of blood pressure control following treatment. Blood pressure response was favorable in 37 patients, but failed to show any improvement in 14. The scintigraphic test was positive in 33 patients (15 cured, 17 improved, 1 failed) and negative in 18 (3 cured, 2 improved, 13 failed). Sensitivity and specificity for renovascular hypertension was 86.5% and 93%, respectively. For blood pressure cure and improvement, the test had positive and negative predictive values of 97% and 72%, respectively. A positive preoperative captopril renal scintigraphic result is a strong predictor of hypertension curability by renal artery revascularization.

[Effects of various caloric intakes on nitrogen metabolism of the body, the muscles and the viscera during total parenteral nutrition with aminoacidic solution enriched with branched-chain amino acids]

Nitrogen metabolism was studied in ten injured/septic patients by means of a two compartment model, differentiating muscle from non muscle (central) tissue. During fasting muscle tissue loses a consistent amount of aminoacids which is retained in part by central tissue, giving rise to a positive nitrogen balance, whilst three methyl histidine and body nitrogen output are elevated. Total parenteral nutrition (glucose 15 kcal kg-1 day-1, nitrogen 0.30 g kg-1 die-1) improved body nitrogen balance and three methyl histidine excretion, but did not affect significantly either muscle or central nitrogen balance. Increasing caloric support to 30 kcal kg-1 day-1 did not showed any further effect on body nitrogen balance and three methyl histidine, while it improved significantly vs basal muscle nitrogen balance, but did not affect central nitrogen balance.

Essential and non-essential amino acid requirement in injured patients receiving total parenteral nutrition

The metabolic derangements of injury are known to influence nitrogen (N) requirements whilst less is known about individual amino acid (AA) requirements. This study was designed to investigate prospectively N vs AA requirement in 36 injured patients treated with total parenteral nutrition (TPN). The non-protein caloric input was 30 kcal kg-1 day-1 and three AA solutions were assessed containing the same AAs but in different proportion. Overall N intake was set at 0.35 g N kg-1 day-1 for solution A and B and 0.24 g N kg-1 day-1 for solution C. Solution B was similar to A, both being enriched in branched chain AAs (BCAA: 0.69 g kg-1 day-1 in B compared with 0.55 g kg-1 day-1 in A) while decreased in aromatic and sulphurated forms (1.75 times the normal need). Solution C was designed to maintain a daily input of BCAA similar to A (0.52 g kg-1 day-1) but with the supply of aromatic and sulphurated AA between solutions A and B, the supply of other AAs (lysine, theonine, histidine, arginine, glycine) being dependent on the selected N intake. For all the essential AAs the supply was always greater than normal allowances. Increasing BCAA over 0.55 g kg-1 day-1 did not improve N balance when N intake was 0.35 g kg-1 day-1, whilst nutrition with solution C was unable to maintain N balance. Moreover we found indirect evidence that this N intake, 0.52 g kg-1 day-1 was more sparing than 0.37 g kg-1 day-1 of BCAA.(ABSTRACT TRUNCATED AT 250 WORDS)