Patient and occupational dose in neurointerventional procedures

Neurointerventional procedures can involve very high doses of radiation to the patient. Our purpose was to quantify the exposure of patients and workers during such procedures, and to use the data for optimisation. We monitored the coiling of 27 aneurysms, and embolisation of four arteriovenous malformations. We measured entrance doses at the skull of the patient using thermoluminescent dosemeters. An observer logged the dose-area product (DAP), fluoroscopy time and characteristics of the digital angiographic and fluoroscopic projections. We also measured entrance doses to the workers at the glabella, neck, arms, hands and legs. The highest patient entrance dose was 2.3 Gy, the average maximum entrance dose 0.9+/-0.5 Gy. The effective dose to the patient was estimated as 14.0+/-8.1 mSv. Other average values were: DAP 228+/-131 Gy cm(2), fluoroscopy time 34.8+/-12.6 min, number of angiographic series 19.3+/-9.4 and number of frames 267+/-143. The highest operator entrance dose was observed on the left leg (235+/-174 microGy). The effective dose to the operator, wearing a 0.35 mm lead equivalent apron, was 6.7+/-4.6 microSv. Thus, even the highest patient entrance dose was in the lower part of the range in which nonstochastic effects might arise. Nevertheless, we are trying to reduce patient exposure by optimising machine settings and clinical protocols, and by informing the operator when the total DAP reaches a defined threshold. The contribution of neurointerventional procedures to occupational dose was very small.

Biodistribution and dosimetry of 99mTc-BTAP-annexin-V in humans

The purpose of this study was to determine the biodistribution and the associated radiation dose of technetium-99m 4,5-bis(thioacetamido)pentanoyl-annexin-V (99mTc-Apomate), a tracer proposed for the study of apoptosis. Eight patients (including two females) with normal kidney and liver functions were included in the study. An activity of 580 +/- 90 MBq of 99mTc-Apomate was injected intravenously, immediately followed by a dynamic study of 30 frames of 1 min each. At about 1 h, 4 h and 20 h p.i., whole-body scans were acquired. All activity distributions were measured using a dual-head gamma camera. Before injection of activity, a transmission scan with a cobalt-57 flood source had been performed to determine patient attenuation. Blood samples were taken every 10 min during the first hour after injection, and at about 4 and 20 h. Urine and faeces were collected during the first 20 h. Organ uptake was estimated after correction for body background activity, attenuation and scatter. Residence times were calculated from the dynamic and whole-body studies and used as input in the Mirdose 3.1 program to obtain organ doses and effective dose. It was found that radioactivity strongly accumulated in the kidneys and the liver [at 70 min p.i., 28% +/- 8% and 20% +/- 4% of the injected dose (ID), respectively]. Uptake in the target tissues (lymphomas or heart) was negligible from a dosimetric point of view. Extrapolating data from the first 20 h, one finds that approximately 73% of the ID will be excreted in the urine, and 27% in the faeces. The biological half-life of the activity in the total body was 16 +/- 7 h. Some organ doses +/- standard deviation (SD) in microGy/MBq were: kidneys 63 +/- 22, urinary bladder 20 +/- 6, spleen 15 +/- 3, liver 13 +/- 3, upper large intestine 12 +/- 6, lower large intestine 8 +/- 4, testes 6 +/- 2 and red bone marrow 4 +/- 0.7. The effective dose was 7.6 +/- 0.5 microSv/MBq, corresponding to a total effective dose of 4.6 +/- 0.3 mSv for a nominal injected activity of 600 MBq. In conclusion, 99mTc-Apomate has a high uptake in the kidneys and liver--in fact a factor of 1.3-1.6 higher than that found for the previously studied 99mTc-(n-1-imino-4-mercaptobutyl)-annexin-V. The biological half-life is shorter, however, but still long compared with the physical half-life of 99mTc. The faster appearance of activity in the intestines may preclude imaging of apoptosis in the abdomen. The effective dose is within the lower range of values reported for typical 99mTc compounds.

Patient and occupational dosimetry in double contrast barium enema examinations

A new and relatively simple method is presented to distribute total dose-area product (DAP) over a number of projections that model exposure during double contrast barium enema (DCBE) examinations. In addition, hitherto unavailable entrance and effective doses to the physician performing the DCBE examination have been determined. DAP, fluoroscopy time, number of images as well as some patient data were collected for 150 DCBE examinations. For a subset of 50 examinations, the distribution of DAP over 12 hypothetical but representative projections was estimated by measuring the entrance dose in the centre of each of these projections during the complete procedure. Effective dose to the patient was obtained using DAP to effective dose conversion coefficients calculated for each of the 12 projections. Exposure of the worker was quantified by measuring the entrance dose at the forehead, neck, arms, right hand and legs. The sex-averaged effective dose to the patient per examination was 6.4+/-2.1 mSv (mean+/-SD; n=50) and the corresponding DAP was 44+/-22 Gy cm(2). The effective dose to the worker per examination was 0.52 microGy (n=50), whereas the highest entrance dose of 30+/-25 microGy was found for the right arm. The proposed method for deriving the distribution of total DAP over a set of representative projections is much less time consuming than visual observation of patient exposure, whilst accuracy seems acceptable. Entrance and effective doses per examination for workers in DCBE examinations are very low. For a normal workload, doses remain far below the legally established dose limits.

Patient dosimetry of intravenously administered 99mTc-annexin V

Annexin V labeled with 99mTc is evaluated as a potential in vivo marker for tissue with increased apoptosis. Promising results in patients have been obtained with 99mTc-(n-1-imino-4-mercaptobutyl)-annexin V (99mTc-i-AnxV). Because information on biodistribution and radiation burden is desired for the application of any radiopharmaceutical, a dosimetric study of 99mTc-i-AnxV was undertaken.

METHODS

Eight persons with normal kidney and liver functions were included in this study: six patients with myocardial infarction, one with Crohn's disease, and one healthy volunteer. Approximately 600 MBq 99mTc-i-AnxV were injected intravenously immediately before a dynamic study with a dual-head gamma camera in conjugate view mode. In the next 24 h, two to four whole-body scans were acquired. Patient thickness was determined from a transmission scan with a 57Co flood source. Organ uptake was estimated after correction for background, attenuation, and scatter, using a depth-independent buildup factor and an organ-size-dependent attenuation correction. Residence times were calculated from the dynamic and whole-body studies and used as input for the MIRDOSE 3.1 program to obtain organ-absorbed doses and effective dose.

RESULTS

Activity strongly accumulated in the kidneys (21% +/- 6% of the injected dose at 4 h postinjection) and the liver (12.8% +/- 2.2%). Uptake in the target tissues (myocardium or colon) was limited and negligible from a dosimetric point of view. The biologic half-life of activity registered over the total body was 62 +/- 13 h. Of the excreted activity, approximately 75% went to the urine and 25% to the feces. The absorbed dose for the more strongly exposed organs was (in microGy/MBq): kidneys, 93 +/- 24; spleen, 22 +/- 6; liver, 17 +/- 2; testes, 15 +/- 3; thyroid, 10 +/- 6; urinary bladder wall, 7.5 +/- 2.6; and red bone marrow, 5.5 +/- 0.8. The effective dose was 9.7 +/- 1.0 microSv/MBq, corresponding to a total effective dose of 5.8 +/- 0.6 mSv for a nominally injected activity of 600 MBq.

CONCLUSION

99mTc-i-AnxV strongly accumulates in the kidneys and to a lesser degree in the liver. The associated effective dose per MBq is in the midrange of values found for routine 99mTc-labeled compounds. From a dosimetric point of view 99mTc-i-AnxV is therefore well suited for the study of apoptosis in patients.

Motion of the proximal renal artery during the cardiac cycle

In 48 hypertensive patients, the motion of the proximal renal artery during the cardiac cycle was quantified using two-dimensional quantitative flow (QF) measurements and automatic contour detection. Substantial translational motion was observed with an amplitude ranging from 1 to 4 mm. Since motion effectively reduces spatial resolution, the use of motion suppression techniques should be strongly considered for renal MR angiography. J. Magn. Reson. Imaging 2000;12:924-928.

Visualisation of cell death in vivo in patients with acute myocardial infarction

BACKGROUND

In-vivo visualisation and quantification of the extent and time-frame of cell death after acute myocardial infarction would be of great interest. We studied in-vivo cell death in the hearts of patients with an acute myocardial infarction using imaging with technetium-99m-labelled annexin-V-a protein that binds to cells undergoing apoptosis.

METHODS

Seven patients with an acute myocardial infarction and one control were studied. All patients were treated by percutaneous transluminal coronary angioplasty (six primary and one rescue), resulting in thrombolysis in myocardial infarction (TIMI) III flow of the infarct-related artery. 2 h after reperfusion, 1 mg annexin-V labelled with 584 MBq Tc-99m was injected intravenously. Early (mean 3.4 h) and late (mean 20.5 h) single-photon-emission computed tomographic (SPECT) images of the heart were obtained. Routine myocardial resting-perfusion imaging was also done to verify infarct localisation.

FINDINGS

In six of the seven patients, increased uptake of Tc-99m-labelled annexin-V was seen in the infarct area of the heart on early and late SPECT images. No increased uptake was seen in the heart outside the infarct area. All patients with increased Tc-99m-labelled annexin-V uptake in the infarct area showed a matching perfusion defect. In a control individual, no increased uptake in the heart was seen.

INTERPRETATION

Increased uptake of Tc-99m-labelled annexin-V is present in the infarct area of patients with an acute myocardial infarction, suggesting that programmed cell death occurs in that area. The annexin-V imaging protocol might allow us to study the dynamics of reperfusion-induced cell death in the area at risk and may help to assess interventions that inhibit cell death in patients with an acute myocardial infarction.

Plasma FFA utilization and fatty acid-binding protein content are diminished in type 2 diabetic muscle

In this study, we investigated the hypothesis that impairments in forearm skeletal muscle free fatty acid (FFA) metabolism are present in patients with type 2 diabetes both in the overnight fasted state and during beta-adrenergic stimulation. Eight obese subjects with type 2 diabetes and eight nonobese controls (Con) were studied using the forearm balance technique and indirect calorimetry during infusion of the stable isotope tracer [U-(13)C]palmitate after an overnight fast and during infusion of the nonselective beta-agonist isoprenaline (Iso, 20 ng. kg lean body mass(-1) x min(-1)). Additionally, activities of mitochondrial enzymes and of cytoplasmatic fatty acid-binding protein (FABP) were determined in biopsies from the vastus lateralis muscle. Both during fasting and Iso infusion, the tracer balance data showed that forearm muscle FFA uptake (Con vs. type 2: fast 449+/-69 vs. 258 +/-42 and Iso 715+/-129 vs. 398+/-70 nmol. 100 ml tissue(-1) x min(-1), P<0.05) and FFA release were lower in type 2 diabetes compared with Con. Also, the oxidation of plasma FFA by skeletal muscle was blunted during Iso infusion in type 2 diabetes (Con vs. type 2: Iso 446 +/- 274 vs. 16+/-70 nmol. 100 ml tissue(-1) x min(-1), P<0.05). The net forearm glycerol release was increased in type 2 diabetic subjects (P< 0.05), which points to an increased forearm lipolysis. Additionally, skeletal muscle cytoplasmatic FABP content and the activity of muscle oxidative enzymes were lowered in type 2 diabetes. We conclude that the uptake and oxidation of plasma FFA are impaired in the forearm muscles of type 2 diabetic subjects in the overnight fasted state with and without Iso stimulation.

Value of radiological diagnosis of skull fracture in the management of mild head injury: meta-analysis

OBJECTIVES

Head injury is a common event. Most patients sustain a mild head injury (MHI), and management depends on the risk of an intracranial haemorrhage (ICH). The value of a plain skull radiograph as a screening tool for ICH is controversial. The aim of this meta-analysis was to estimate and explain differences in reported sensitivity and specificity of the finding of a skull fracture for the diagnosis of ICH, in order to assess the value of the plain skull radiograph in the investigation of patients with MHI, and to estimate the prevalence of ICH in these patients.

METHOD

After a systematic literature search 20 studies were selected that reported data on the prevalence of ICH after MHI and/or data on the diagnostic value of skull fracture for the diagnosis of ICH. The mean prevalence of ICH weighted for the sample size was determined. The sensitivity and specificity of different studies were combined using a summary receiver operator characteristic curve. Correlation analysis was used to determine factors that could explain the reported differences between studies.

RESULTS

The weighted mean prevalence of ICH after MHI is 0.083. The potential for verification bias and the percentage of patients who had suffered loss of consciousness or post-traumatic amnesia were the most significant factors explaining interstudy differences in sensitivity and specificity. Based on studies wherein at least 50% of patients had a CT study of the brain, the estimated sensitivity of a radiographic finding of skull fracture for the diagnosis of ICH is 0.38 with a corresponding specificity of 0.95.

CONCLUSION

The plain skull radiograph is of little value in the initial assessment of MHI patients.

Microdialysis assessment of local adipose tissue lipolysis during beta-adrenergic stimulation in upper-body-obese subjects with type II diabetes

The present study was designed to investigate indicators of abdominal adipose tissue lipolysis (microdialysis), and subcutaneous adipose tissue blood flow and whole-body lipolysis, in obesity-associated type II diabetes during overnight-fasted conditions (baseline) and during intravenous infusion of the non-selective beta-agonist isoprenaline. Basal subcutaneous adipose tissue blood flow and isoprenaline-induced increases in adipose tissue blood flow were not significantly different between subjects with type II diabetes and non-obese, non-diabetic controls. Adipose tissue interstitial glycerol concentrations were significantly higher in subjects with type II diabetes compared with controls (P<0. 01), and during isoprenaline infusion there was a decrease in interstitial glycerol in both groups (P<0.001). Arterial glycerol concentrations were higher in subjects with type II diabetes compared with controls (P<0.05), whereas the increases in arterial glycerol concentration in response to isoprenaline infusion were of a similar magnitude in the two groups. Estimated subcutaneous adipose tissue glycerol release was not significantly different between the groups (controls and subjects with type II diabetes: baseline, -129+/-32 and -97+/-72 micromol.min(-1).100 g(-1) adipose tissue respectively; isoprenaline, -231+/-76 and -286+/-98 micromol. min(-1).100 g(-1) respectively). Values for fat oxidation were not significantly different between groups, whereas the isoprenaline-induced increase in fat oxidation tended to be less pronounced in subjects with type II diabetes compared with controls (0.022+/-0.008 and 0.038+/-0.003 g/min respectively; P=0.058). Thus estimated basal subcutaneous adipose tissue glycerol release, expressed per unit of fat mass, is not different in controls and in subjects with type II diabetes. Additionally, the isoprenaline-induced increases in indicators of local abdominal subcutaneous adipose tissue, systemic lipolysis and abdominal adipose tissue blood flow responses were comparable in obese subjects with type II diabetes and in controls. The last two findings contrast with previous data from obese subjects, indicating that the regulation of lipolysis may differ in obesity and obesity-associated type II diabetes.

Quantitative analysis of magnetization transfer images of the brain: effect of closed head injury, age and sex on white matter

Magnetization transfer (MT) imaging has an application in quantitative assessment of cerebral white matter. Previously published postprocessing methods have inherent problems, and therefore a new analysis technique is presented. This technique was found to be more sensitive for white matter changes in patients with a postconcussional syndrome, compared to other methods previously described. Because of the potential application of this technique in longitudinal and group studies, age and sex dependence of the MT ratio (MTR) of white matter were studied. In a group of 51 healthy subjects, a decrease in the mean MTR as well as an increasing distribution width of the MTR was found with increasing age. The mean MTR in males was higher than in females. These results stress the need to take age and sex into account when interpreting MTR data. Magn Reson Med 42:803-806, 1999.

Improving contrast and tracking of tags in cardiac magnetic resonance images

Cardiac tagging permits non-invasive study of myocardial motion with high accuracy. Unfortunately, tagging contrast is impaired at later heart phases due to longitudinal relaxation. Histogram modification is presented as a method for improving contrast in later, faded images of a tagging series by altering these images such that their intensity histograms approximate the shape of the first, unfaded image of the series. This technique greatly improves the contrast and facilitates automatic detection of tags. Furthermore, a method is described for automatically tracking tag positions in short-axis images of the left ventricle modulated with a tagging grid. The method differs from previously reported methods in that, in one single filtering process in the Fourier domain, both the grid crossings as well as the grid centers are detected, and thus increased sampling resolution is obtained. The method was validated by applying a mathematical model of left ventricular motion to tagged images of the thigh muscle. The average discrepancy between theoretically predicted and automatically detected tag positions was 0.04 +/- 0.17 mm (mean +/- SD).

Patient dosimetry in abdominal arteriography

This study aims at accurate quantification of x-ray exposure and effective dose to the patient in abdominal arteriography. Using an automatic monitoring system, all relevant exposure parameters were determined during 172 abdominal arteriographies. Common projections were extracted for a 'normal' reference group of procedures and used in Monte Carlo calculations of dose-area product to organ dose conversion coefficients. Dose-area product, organ doses and effective dose were quantified for intravenous and intra-arterial procedures. The large data sets describing exposure could be condensed to a set of 28 common views. New coefficients to convert dose area product to organ equivalent dose and effective dose were calculated for nine views contributing approximately 80% to the total dose-area product. The average dose-area product was 32 Gy cm2 in intravenous procedures and 47 Gy cm2 in intra-arterial procedures. The corresponding average effective doses to the patient were 4 mSv and 6 mSv respectively (range 2-12 mSv, actual value depending on procedure type and gender). It is concluded that automatic monitoring of x ray exposure parameters, complemented by the calculation of Monte Carlo organ dose conversion coefficients, is a feasible and promising approach to accurate dosimetry of complex arteriographic procedures.

On segmentation of lung parenchyma in quantitative computed tomography of the lung

Our purpose in this study was to investigate the influence of segmentation threshold and number of erosions on parameters used in quantitative computed tomography (CT) of the lung (erosions are shrink operations on the segmented area). Parameters assessed were mean lung density, area of the segmented lung, two percentiles, and the pixel index, which is the relative area of the histogram below -905 Hounsfield Units (HU). We analyzed images of ten emphysematous and ten nonemphysematous patients, that had been scanned at carina level in inspiration and expiration, using sections of 1, 2, 3, 5, and 10 mm in combination with a standard, a smooth, and an ultrasmooth reconstruction kernel. The lungs were segmented using pixel tracing at thresholds of -200, -400, and -600 HU with 0-4 erosions, followed by histogram analysis. The area of the segmented lungs decreased with 0.9%-3.2% per 100 HU decrease in threshold and with 2.2%-3.1% per erosion, dependent on patient group and respiratory status. Estimated mean lung density changed up to 30% by changing the threshold and the number of erosions. The pixel index and the 10th percentile depended only slightly on threshold and number of erosions, but the 90th percentile showed a strong dependence of up to 40%. It is concluded that the segmentation protocol can have a large impact on densitometric parameters and that standardization is mandatory for obtaining comparable results. Ideally a threshold equal to the average of the densities of lung and soft tissue should be used, but -400 HU will do in a limited but common density range (-910 to -790 HU). For densitometry two erosions are recommended, for volumetry zero erosions should be used.

Reproducibility of spirometrically controlled CT lung densitometry in a clinical setting

The aim of this study was to assess the reproducibility of quantitative, spirometrically gated computed tomographic (CT) lung densitometry at defined levels of inspiration in hospitalized patients. On two consecutive days, spirometrically gated CT sections were obtained from 20 hospitalized patients at 5 cm above and 5 cm below the carina, and at 90 and 10% of the vital capacity (VC). The mean, modal and median lung densities were calculated, the cut-off points of the frequency distribution of Hounsfield units (HU) defining the lowest and the highest 10th percentile, as well as the histogram full width at half maximum. The lung density parameters of corresponding CT sections of both studies were compared. Reproducibility was expressed as the standard deviation of the signed difference between the results of Day 1 and Day 2 divided by the square root of 2. Reproducibility data were correlated with results of airflow limitation. At 90% VC, reproducibility was of the order of 3-14 HU in both lung zones. At 10% VC, reproducibility was worse by approximately a factor of three. No relationship was found between reproducibility and results of airflow limitation. In conclusion, objective measurement of lung density at spirometrically controlled levels of inspiration is a reproducible method in assessing pulmonary density. Reproducibility of lung density measurements is not influenced by severe respiratory insufficiency. The most reproducible computed tomographic lung density measurements can be obtained at 90% vital capacity.

CT lung densitometry: dependence of CT number histograms on sample volume and consequences for scan protocol comparability

PURPOSE

Our goals were to determine the dependence of CT number histograms of the lung on section thickness and reconstruction filter and to evaluate the consequences for scan protocol conformity required for universally comparable densitometry of the lungs.

METHOD

The effects of section thickness and reconstruction filter were parameterized with the CT's sample volume [V approximately (section thickness x in-plane resolution2)]. In a study of 31 patients, we determined as a function of V the following CT number histogram parameters: percentiles P(10) and P(90), pixel indexes PI(-905) and PI(-950), and standard deviation.

RESULTS

Patient histogram parameters depended strongly on sample volume. Large differences were found between protocols using 1 and 10 mm sections. For small variations in somewhat larger sample volumes (> 8 mm3), discrepancies were much smaller.

CONCLUSION

To obtain comparable histogram parameters, nearly identical sample volumes (> or = 8 mm3) should be used. When this condition is satisfied, available data suggest that universally comparable densitometry is feasible.

The CT's sample volume as an approximate, instrumental measure for density resolution in densitometry of the lung

Ultimately CT-densitometry of the lung should give comparable results on all scanners. One prerequisite for this is the use of the same density resolution. Unfortunately, density resolution is impractical as a performance specifying parameter because it depends on the cellular material scanned. Therefore, another parameter that can be used for scanner and protocol characterization, and that does not depend on a special phantom, would be highly preferable. We investigated how well the CT's nominal sample volume (V), calculated from section thickness and in-plane spatial resolution as specified by the CT manufacturer, can serve as a simple measure, for density resolution. Six CT scanners were studied using foam and lung phantoms. On all scanners we observed for foam an approximately linear relation between density resolution and V-1/2. Density resolution on different scanners varied to some extent. These differences can be interpreted as being caused by deviations of the true sample volume from the nominal value: the 95%-confidence interval runs for instance for V = 8 mm3 from 4.6 mm3 to 16.9 mm3. Acceptability of this spread depends on the consequences for parameters of clinical interest, like percentiles and pixel indexes. To evaluate this we used data from a previous patient study on the dependence of histogram parameters on sample volume. With these data it is found that large interscanner differences in histogram parameters are possible for small values of V, as used in thin-section densitometry. For larger values of V, as required for a more adequate density resolution, the differences are much smaller and probably acceptable when compared to other sources of variability in lung densitometry. In conclusion, for sections of at least 2 mm and smooth reconstruction filters, corresponding to V > or = 8 mm3, the CT's nominal sample volume might be used for interscanner and interprotocol comparison of density resolution.

The effect of a single rectal dose of cisapride on delayed gastric emptying

BACKGROUND

Cisapride has an established prokinetic effect in patients with delayed gastric emptying. However, rectal administration of the drug might be preferred in patients with either dysphagia or nausea due to gastroparesis.

AIM

To determine the effect of a single rectal dose of cisapride 60 mg on gastric emptying in patients with delayed gastric emptying.

METHODS

Thirty-two patients (16 males, 16 females) with demonstrated delayed gastric emptying received a single dose of two suppositories containing either cisapride (2 x 30 mg) or placebo, according to a double-blind randomized crossover design. Three hours after administration of the suppositories, the patients received a radio-labelled test meal and radio-opaque markers for measurement of gastric emptying.

RESULTS

The mean t1/2 after cisapride administration (76 min, 95% CI: 68-95) was significantly shorter (P = 0.005: n = 28, per-protocol analysis) than after placebo administration (104 min, 81-126). Four hours after ingestion of the meal significantly fewer radio-opaque markers remained in the stomach after cisapride than after placebo administration (P < 0.05). Mild to moderate adverse events, mainly involving the gastrointestinal tract, were reported in 10 patients (31%) after cisapride treatment and in four patients (13%) after placebo (N.S.: n = 32).

CONCLUSION

A single suppository dose of cisapride 60 mg significantly accelerates gastric emptying of the solid phase of a meal and of radio-opaque markers in patients with previously demonstrated delayed gastric emptying.

Baseline and postcaptopril renal blood flow measurements in hypertensives suspected of renal artery stenosis

Renal blood flow (RBF) measurements using first-pass radionuclide angiography with DTPA, a glomerularly filtered agent, failed to show significant differences between normal and stenotic kidneys. Since MAG3 is an ideal agent for the study of RBF, this agent might be an attractive alternative tracer to detect differences in RBF.

METHODS

An angiographically controlled prospective study was performed in 48 hypertensive patients, in whom a diagnosis of renovascular hypertension was suspected on clinical grounds. The study was done to determine whether RBF measurements using first-pass radionuclide angiography with 99mTc-MAG3 could be helpful in the diagnostic work-up of the patients. Additionally, the study was done before and after ACE-inhibition.

RESULTS

On renal angiography, 29 patients showed to have normal renal arteries (50 patients had normal kidneys and 8 patients had small kidneys). Nineteen patients had renal artery stenosis (13 uni- and 6 bilateral disease). In the patients with normal kidneys, the mean value of RBF measurements ranged from 10.5% to 10.9% of cardiac output. Only small stenotic and small kidneys with normal renal arteries showed a significant reduced baseline RBF as compared with normal kidneys (both p < 0.05); this difference disappeared after ACE-inhibition only for the small kidneys with normal renal arteries. In patients with stenosed kidneys, RBF tended to be reduced both at baseline and after captopril, but the differences with normal kidneys were not statistically significant. After ACE-inhibition RBF increased in the majority of kidneys, but postcaptopril RBF data did not differ significantly from those at baseline.

CONCLUSION

RBF measurements using first-pass radionuclide angiography with 99mTc-MAG3, either before or after ACE-inhibition, cannot reliably discriminate between patients with essential hypertension and patients with renal artery stenosis.

Density resolution in quantitative computed tomography of foam and lung

This study was performed to assess density resolution in quantitative computed tomography (CT) of foam and lung. Density resolution, a measure for the ability to discriminate materials of different density in a CT number histogram, is normally determined by quantum noise. In a cellular solid, variations in mass in the volumes sampled by CT cause an additional degradation of density resolution by the linear partial volume effect. The sample volume, which is directly related to spatial resolution, can be varied by choosing different section thicknesses and reconstruction filters. Several polyethene (PE) foams, as simple models of lung tissue, and five patients were investigated using various sample volumes. For the uniform PE foams, density resolution could be directly determined as the full width at half maximum of CT number histograms. Density resolution for foams with cell sizes of 0.8-1.5 mm was dominated by effects caused by the limited sample size, not by quantum noise. The relative magnitudes of density resolution could roughly be explained with a model for a hypothetic random cellular solid. Since lungs are not of uniform density, analysis of patient data was more complicated. A combined convolution least-squares fit procedure, together with information obtained in the studies of foam, were used to determine density resolution in lung studies. Density resolution, both for foams and lung, was strongly dependent on sample volume, and was quite poor for thin sections and sharp filters. Consequently, histogram-shape related parameters are sensitive to the spatial resolution chosen on CT. Thin section densitometry, using a 1-mm section with a standard or high resolution filter, is not recommended except in determining average density. When using thicker sections, an in-plane spatial resolution similar to section thickness is advised.

On the generation of short-axis and radial long-axis slices in thallium-201 myocardial perfusion single-photon emission tomography

We tried to develop fully automatic reorientation algorithms in thallium-201 myocardial perfusion single-photon emission tomography, and tested a method to evaluate the quality of reorientation. The left ventricle was automatically segmented using count density information, contours generated with Laplacian operators in both transaxial and sagittal slices, and morphological and positional characteristics of the contours. Reorientation was automatically performed based on knowledge of the long axis of a second degree surfac fitted to the myocardial wall. We tried to achieve improvement in reorientation without relying on any functional description of left ventricular shape. Quality of reorientation was evaluated and improved using interactive tools in combination with radial long-axis slices. Two groups of 50 patients, after stress and rest, were analysed using the traditional manual and the fully automatic procedures. Automatic segmentation was successful in 98 out of 100 cases, and automatic reorientation was of reasonable quality. Reorientation obtained with the radial long-axis slices tool was better than after traditional manual or automatic reorientation. Automatic reorientation based on second degree surface fitting was in our hands less successful than reported in the literature. The tool using radial long-axis slices provides a better standard for testing reorientation algorithms than the traditional manual method.

CT densitometry of the lungs: scanner performance

OBJECTIVE

Our goal was to establish the reproducibility and accuracy of the CT scanner in densitometry of the lungs.

MATERIALS AND METHODS

Scanner stability was assessed by analysis of daily quality checks. Studies using a humanoid phantom and polyethylene foams for lung were performed to measure reproducibility and accuracy. The dependence of the CT-estimated density on reconstruction filter, zoom factor, slice thickness, table height, data truncation, and objects outside the scan field was determined.

RESULTS

Stability of the system at air density was within approximately 1 HU and at water density within approximately 2 HU. Reproducibility and accuracy for densities found for lung were within 2-3%. Dependence on the acquisition and reconstruction parameters was neglible, with the exceptions of the ultra high resolution reconstruction algorithm in the case of emphysema, and objects outside the scan field.

CONCLUSION

The performance of the CT scanner tested is quite adequate for densitometry of the lungs.

Scanner conformity in CT densitometry of the lungs

PURPOSE

To quantify inter- and intrascanner conformity in computed tomographic (CT) densitometry of the lungs.

MATERIALS AND METHODS

With six scanners from four manufacturers, a lung densitometry protocol with several variations was applied for performance comparison. Phantoms included water, air, and a humanoid thorax phantom equipped with a dog lung and exchangeable pseudolungs of polyethylene foam.

RESULTS

All scanners produced acceptable CT numbers (Hounsfield units) for water, but some not for air. An incorrect calibration of air density affected all CT numbers at lung densities, but the error was easily correctable. Some systems were more sensitive to object size than others were. Sensitivity of CT numbers to section thickness, reconstruction filter, zoom factor, and table height was small, except for two scanners in relation to section thickness.

CONCLUSION

After correction for poor air calibration, scanner conformity was acceptable when the reproducibility of lung densitometry in clinical practice was set as a reference.

The nonlinear partial volume effect and computed tomography densitometry of foam and lung

A quantitative study was performed to assess the magnitude of the nonlinear partial volume effect (NLPVE) in computed tomography (CT) densitometry of polyethene foam and lung. This effect arises in materials having density variations on the scale of the sampling area of an individual CT-detector element. It causes a systematic underestimation of the density determined with CT. Foam samples and a resected lung of a goat were imaged with high resolution (20 lp/mm) using a mammography system, and the observed optical density variation in the images was converted into a distribution of pathlengths that x rays penetrate within the solid component of the cellular material. The obtained pathlength distribution was used to calculate the transmission, as seen by a single detector in computed tomography. Comparison with the transmission through homogeneous material of the same thickness gave an estimate of the NLPVE. For the foams studied, the CT-determined density was found to be too low by approximately 0.3%-0.5% due to this effect. Although these density errors are small, in calibrations of a CT scanner they may be of significance. For lung the underestimation of the density was less than 0.1%. These experimentally derived, NLPVE related CT-density errors are 32%-84% of those calculated from a simple model of a cellular solid.

Vascular radiology in The Netherlands in 1992: a quantitative approach

A survey was held into methods and extent of vascular radiology in the Netherlands. For the year 1992, quantitative data on the number of patients, vascular radiological examinations and characteristics of angiography facilities were obtained from more than 80% of the Dutch hospitals with angiography rooms (120). The following estimates have been inferred: approximately 50,600 patients were referred for non-cardiac vascular radiology, including 32,100 patients for intra-arterial arteriography, 8900 for intravenous DSA arteriography, 4600 for phlebography and 5000 for interventional radiology. On average about two vascular examinations were carried out per patient referred for arteriography. In interventional radiology, the number of patients and the number of examinations are quite similar. The total number of angiography rooms in the Netherlands was 136. The average age of angiography X-ray systems was 7.1 years, of imaging equipment 5.7 years. In 56% of the hospitals, the X-ray tube was normally applied in the undercouch position, in 40% in overcouch position and in 4% there was no preferred position. An additional survey of occupational exposure conditions in angiography rooms (19 hospitals) showed that, in most hospitals, protective lead aprons of 0.5 mm Pb-equivalent were in use. Thyroid collars were used rather infrequently.