Idiopathic pulmonary artery aneurysm: digital subtraction pulmonary angiography grossly underestimates the size of the aneurysm

Pulmonary artery aneurysm is a rare disease entity. The majority of cases are associated with congenital cardiovascular diseases, infection, and trauma; idiopathic pulmonary artery aneurysm is extremely rare. Although conventional and digital subtraction pulmonary angiography remains as the imaging modality of choice for the pulmonary vessels, it is invasive and sometimes may be inaccurate. With the advent of spiral computed tomographic angiography (CTA), pulmonary artery aneurysm can be diagnosed noninvasively and accurately. We report a case of a 68-year-old man with idiopathic pulmonary artery aneurysm of the descending branch of right pulmonary artery where the true caliber of the aneurysm was significantly underestimated in the digital subtraction pulmonary angiography. The literatures of this rare condition are reviewed with the emphasis on the application of CTA in this disease.

Reduction of radiation dose to patients undergoing barium enema by dose audit

Nowadays, new fluoroscopic machines are usually equipped with a dose-area product (DAP) meter for dose measurement. In our hospital, DAP meters have been used in the Diagnostic Radiology Department for dose audit since June 1997. Demographic patient data, name of radiologist, fluoroscopic duration and DAP readings of every case were recorded by radiographers. In early 1999, questionnaires were distributed to radiologists who had performed fluoroscopic examinations during the auditing period. 23 radiologists with varying years of experience completed the questionnaire and their practice was analysed. Since familiarization with the examination technique would affect radiologists' practice, these radiologists were divided into two groups for analysis. Radiologists with less than 3 years of experience were grouped together as junior radiologists, whilst others were grouped as senior radiologists. Results of the questionnaire indicated that radiologists generally found DAP meters useful for dose evaluation in the process of technique refinement. Radiologists aware of being under continuous surveillance of their practice showed significant reduction of doses (junior radiologists 25%, p<0.005; senior radiologists 36%, p<0.05) and fluoroscopic times (junior radiologists 36%, p<0.001; senior radiologists 18%, p<0.05) compared with radiologists who were unaware that they were under surveillance but with similar radiological experience. This effect is believed to be because of increased awareness of radiation dose through audit. In addition, this "audit effect" may also affect junior radiologists in decision-making regarding the number of radiographs (p<0.05), but no effect was found for senior radiologists (p>0.5).

Experimental lung transplantation using non-penetrating vascular clips for anastomosis of the pulmonary artery

BACKGROUND

Reliable and rapid anastomosis is critical in lung transplantation. The purpose of this study is to show the appropriateness of sutureless anastomosis of the pulmonary artery using a nonpenetrating vascular clipping device.

METHODS

The left lung was excised and the cranial lobe was transplanted autologously in 9 dogs. The anastomosis of the left main pulmonary artery (PA) (1 cm) was performed using a vascular clipping system.

RESULTS

PA anastomosis was performed in 7 dogs in 8 to 13 minutes. The endovascular surface of the anastomotic site was smooth, and passage of silicone rubber through the anastomosis was good 14 or 28 days after surgery. Microscopic examination of the anastomotic sites showed excellent healing without evidence of intimal hyperplasia.

CONCLUSIONS

The vascular clipping system facilitates anastomosis of the PA in lung transplant surgery.

Radiation dose reduction in paediatric cranial CT

BACKGROUND

There is no consensus about the optimal milliamperage-second (mAs) settings for computed tomography (CT). Most operators follow the recommended settings of the manufacturers, but these may not be the most appropriate settings.

OBJECTIVE

To determine whether a lower radiation dose technique could be used in CT of the paediatric brain without jeopardising the diagnostic accuracy of the images.

MATERIALS AND METHODS

A randomised prospective trial. A group of 53 children underwent CT using manufacturer's default levels of 200 or 250 mAs; 47 underwent scanning at 125 or 150 mAs. Anatomical details and the confidence level in reaching a diagnosis were evaluated by two radiologists in a double-blinded manner using a 4-point scoring system.

RESULTS

For both readers there was no statistically significant difference in the confidence level for reaching a diagnosis between the two groups. The 95 % confidence intervals and P values were -0.9-1.1 and 0.13 (reader 1) and -1.29-1.37 and 0.70 (reader 2), respectively. Reliability tests showed the results were consistent.

CONCLUSIONS

The recommended level may not be the optimum setting. Dose reduction of 40 % is possible on our system in paediatric brain CT without affecting the diagnostic quality of the images.

Segmented attenuation correction using artificial neural networks in positron tomography

The measured attenuation correction technique is widely used in cardiac positron tomographic studies. However, the success of this technique is limited because of insufficient counting statistics achievable in practical transmission scan times, and of the scattered radiation in transmission measurement which leads to an underestimation of the attenuation coefficients. In this work, a segmented attenuation correction technique has been developed that uses artificial neural networks. The technique has been validated in phantoms and verified in human studies. The results indicate that attenuation coefficients measured in the segmented transmission image are accurate and reproducible. Activity concentrations measured in the reconstructed emission image can also be recovered accurately using this new technique. The accuracy of the technique is subject independent and insensitive to scatter contamination in the transmission data. This technique has the potential of reducing the transmission scan time, and satisfactory results are obtained if the transmission data contain about 400,000 true counts per plane. It can predict accurately the value of any attenuation coefficient in the range from air to water in a transmission image with or without scatter correction.

Single-photon transmission measurements in positron tomography using 137Cs

Transmission measurements are an essential step in the quantification of radioisotope distributions in vivo using positron tomographic techniques. The development of a new technique for measuring transmission data that relies on the detection of photons in 'singles' mode rather than 'coincidence' mode no longer restricts the choice of transmission sources to those that decay by positron emission. The motivation for using the 'singles' mode of operation is the substantial increase in count rate that can be achieved. This corresponds to a great increase in the statistical accuracy of the transmission data. We propose 137Cs as a suitable isotope for this purpose. 137Cs is more economical than 68Ge, the traditional source used for transmission measurements, in terms of longer half-life and lower financial cost. 137Cs can be used for transmission measurements without any recalibration of the tomograph, and the estimated spatial resolution is comparable to that obtained using annihilation photons. A simple extrapolation method is developed, which allows extrapolation of the attenuation coefficients measured at 662 keV to 511 keV. A dual-energy-window technique, whereby correction can be made on-the-fly during acquisition, is used for scatter correction. The measured linear attenuation coefficients agree with predicted values.

Effect of tissue inhomogeneity on dose distribution of continuous activity of low-energy electrons in bone marrow cavities with different topologies

Monte Carlo calculations have previously been performed by Eckerman to evaluate the absorbed fractions of continuous sources of monoenergetic electrons in marrow cavities of human bone. The difference in scattering power of electrons in cortical bone (CB) and the red marrow (RM) was neglected. In the present work the Integrated Tiger Series and Electron-Gamma-Shower Monte Carlo codes were used to investigate the effect of topology of the bone and bone marrow interface on backscatter dose increase to the marrow. Planar, cylindrical, and spherical geometries were included. For the planar geometry, a maximum dose increase of 9 +/- 1 (S.E. of the mean) % was obtained in the region within 12 mg/cm2 from the interface due to a semi-infinite source of electrons with energy greater than 0.5 MeV. An increase of 7 +/- 1% was observed experimentally in the same region due to a semi-infinite source of 32P. This was in good agreement with Monte Carlo calculation. Averaged over the region of RM embedding electron sources between two planar CB/RM interfaces 1000 microns apart, a dose enhancement of 10 +/- 2% was predicted for electron energies from 1 to 1.75 MeV. For the cylindrical interface with 500-microns radius of curvature, the maximum dose increase averaged over the whole cylinder due to an isotropic distribution of monoenergetic electrons inside the cylinder was 12 +/- 1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of tissue inhomogeneity on dose distribution of point sources of low-energy electrons

Perturbation in dose distributions of point sources of low-energy electrons at planar interfaces of cortical bone (CB) and red marrow (RM) was investigated experimentally and by Monte Carlo codes EGS and the TIGER series. Ultrathin LiF thermoluminescent dosimeters were used to measure the dose distributions of point sources of 204Tl and 147Pm in RM. When the point sources were at 12 mg/cm2 from a planar interface of CB and RM equivalent plastics, dose enhancement ratios in RM averaged over the region 0-12 mg/cm2 from the interface were measured to be 1.08 +/- 0.03 (SE) and 1.03 +/- 0.03 (SE) for 204Tl and 147Pm, respectively. The Monte Carlo codes predicted 1.05 +/- 0.02 and 1.01 +/- 0.02 for the two nuclides, respectively. However, EGS gave consistently 3% higher dose in the dose scoring region than the TIGER series when point sources of monoenergetic electrons up to 0.75 MeV energy were considered in the homogeneous RM situation or in the CB and RM heterogeneous situation. By means of the TIGER series, it was demonstrated that aluminum, which is normally assumed to be equivalent to CB in radiation dosimetry, leads to an overestimation of backscattering of low-energy electrons in soft tissue at a CB-soft-tissue interface by as much as a factor of 2.

Shear stress-induced changes in platelet reactivity

We have investigated the effects on platelet function of a physiologic shear stress. The aggregation to thrombin and collagen, the release reaction [(14C) serotonin] and the procoagulant activity of washed platelet suspensions were assayed on samples undergoing laminar oscillatory flow for 20 minutes at 37 degree C in polyethylene tubes, and on paired samples kept at rest. The pulse rate was established at 72 cycles per minute and the shear stress at the wall estimated at 26.2 dynes/cm2. The platelet suspensions were prepared at 37 degree C from blood samples of 15 healthy volunteers and 15 patients with the diagnosis of coronary artery disease proven by angiography. Our results show enhancement of platelet aggregation in samples undergoing oscillatory flow. Furthermore, platelets from coronary patients gained additional procoagulant activity. However, no change was encountered in the rate and speed of the release reaction. It is concluded that exposure to a high shear stress within an oscillatory flow system enhances platelet reactivity; this reaction may take part in the production of platelet and coagulation changes seen in the atherosclerotic patient and after strenuous physical exercise.

Potentiation by alpha and inhibition by beta-adrenergic stimulations of rat platelet aggregation. A comparative study with human and rabbit platelets

Epinephrine, known to potentiate and elicit aggregation of human platelets, was shown to inhibit thrombin-induced aggregation of rat platelets, delaying the onset of aggregation from 2 to 12 times. Incubation of rat platelet suspensions with propranolol (1.25--30 micrometer), inactive by itself, totally prevented the inhibitory effect of epinephrine and also permitted a potentiation effect to show up. On the contrary, phentolamine (1.25--30 micrometer) potentiated the inhibitory effect of epinephrine on rat platelets and unmasked an inhibitory effect on human platelets. Finally, isoproterenol (0.25--9 micrometer) produced a marked inhibition of aggregation induced by thrombin, ADP and collagen in the three species studied, but most particularly in the rat. From these results, we conclude that stimulation of the platelet adrenergic receptors may either result in promotion (alpha-stimulation) or inhibition (beta-stimulation) of platelet aggregation. Furthermore, differences in the ratios or responses of alpha/beta receptors may account for species variations in the platelet aggregation response to catecholamine challenge.