D. N. Croft

Ventilation-Perfusion Lung Scanning for Pulmonary Emboli

The conventional method of lung scanning detects defects of pulmonary artery perfusion. False positive results occur because regions of hypoventilation, such as are present in obstructive airways disease, also cause defects of perfusion. The converse is not true, however, as defects of perfusion continue to be ventilated. Thus in pulmonary embolism ventilation-perfusion discrepancy (normal ventilation and impaired perfusion) occurs. We have assessed the clinical value of this discrepancy. Out of 18 patients with ventilation-perfusion discrepancy 14 had a final diagnosis of pulmonary emboli, whereas in none of the 34 patients without the discrepancy was this final diagnosis made. We conclude that combined ventilation-perfusion lung scanning distinguishes pulmonary emboli from other lung conditions such as asthma and bronchitis which cause impaired pulmonary perfusion. The false positive rate was only 4% overall and 7·7% in patients with perfusion defects.

Effect of intravenous dextran 70 and pneumatic leg compression on incidence of postoperative pulmonary embolism.

The incidence of pulmonary embolism and deep vein thrombosis was measured in 50 matched pairs of patients undergoing common surgical procedures with preoperative and postoperative ventilation-perfusion lung scans and the fibrinogen uptake test. One patient in each pair was treated with intravenous dextran 70 and pneumatic leggings. The incidence of pulmonary embolism among the treated patients was significantly reduced from 24% to 8%, but the incidence of deep vein thrombosis was not significantly reduced (34% to 24%).

Radionuclides and therapy of thyroid cancer

The majority of thyroid carcinomas are removed surgically. The appropriate surgical technique is still debated. After surgery the amount of residual thyroid or tumour and the presence of local or distant metastases is often in doubt, particularly if it is not detectable clinically. Therefore, methods for determining the presence of disease or the later recurrence of disease are needed. They commonly include serum thyroglobulin and imaging after diagnostic or therapeutic doses of 131I. Other techniques are used such as 131I whole body retention (using a whole body counter), 201Tl and 99Tcm-sestamibi imaging. The place of these diagnostic methods in the management of thyroid cancer is reviewed in this article. Radioiodine would seem an ideal treatment for recurrence of functioning thyroid carcinoma as 131I targets the lesion and has minimal side effects. However, the indolent nature of well-differentiated thyroid carcinomas makes it difficult to assess the benefits of radioiodine therapy both in its ability to ablate the normal thyroid and to treat recurrent and metastatic disease. However, the addition of radioiodine therapy to local surgical removal reduces both the occurrence of metastases and the morbidity with prolonged follow-up. Unresolved issues that remain concern the activities of radioiodine needed to achieve adequate ablation of residual thyroid tissue and to treat residual and recurrent cancer. There is also debate as to exactly which patients require radioiodine therapy. This review also considers radiation protection and the side effects of 131I therapy.

Ventilation-perfusion lung scans for pulmonary emboli

Reports were made on combined ventilation-perfusion lung scans by three observers on three occasions and by another observer once. Reproducibility for each observer varied between 80 and 88%. There was complete agreement about the areas of scans reported as abnormal. Agreement between observers on whether or not the abnormality represented a pulmonary embolus averaged 77%. There was 86% agreement with the final clinical diagnosis. Our results show that reporting of ventilation perfusion lung scans by eye is reproducible. They support the claims that, under routine clinical conditions, the technique is 91% to 95% accurate for pulmonary emboli.

Assessment of pulmonary ventilation scans using xenon-127 in the diagnosis of pulmonary embolism.

Pulmonary ventilation scans using 127Xe were compared with scans using 133Xe in the diagnosis of pulmonary embolism. A perfusion scan using 99mTc-microspheres and ventilation scans with each of the xenon isotopes were performed on 44 patients referred for lung scanning to confirm or exclude a suspected clinical diagnosis of pulmonary embolism. No significant difference was found in the frequency of diagnosis of pulmonary embolism when comparing each of the ventilation scans with the corresponding perfusion scan. For reasons discussed, 127Xe may be more useful than 133Xe for pulmonary ventilation scanning.

Pulmonary Permeability in Hematologic Malignancies Effects of the Disease and Cytotoxic Agents

Pulmonary permeability was assessed using the technique of DTPA aerosol transfer in untreated patients with chronic lymphocytic leukemia (CLL) and in patients with a variety of hematologic malignancies that had all been treated with alkylating agents. Two findings emerged: (1) In the untreated CLL patients, the permeability of the upper and middle lung regions was reduced. This may be due to diffuse infiltration by the CLL; and (2) Treatment with cytotoxic agents increased epithelial permeability in both middle and lower lung regions. Further prospective studies are required to determine the cause of the long T50 values in untreated CLL and to confirm that the DTPA transfer test is a sensitive indicator of the damage which eventually leads to pulmonary fibrosis.

111In-Leukocyte imaging: Intrasplenic abscesses

A 52-year-old female patient was routinely referred for an indium-111 white-cell scan due to elevated white blood cell count after nitral-valve replacement. A scan with technetium-99m tin colloid was also performed, and the resulting subtraction image showed two areas of whitecell accumulation within the spleen which were presumed to be abscesses. This was confirmed at postmortem examination.

Functional images of lung 99Tcm-DTPA aerosol transfer in smokers and nonsmokers.

The large amount of information from dynamic 99Tcm-DTPA lung can be simplified and rendered easily interpretable by the use of functional images. Eight such images have been devised: a maximum count image, a minimum count image, a time of maximum count image, a time of minimum count image, percentage maximum change image, a T50 image, a standard error image and a correlation coefficient image.These images enable the distribution of aerosol after inhalation, the reliability of the calculated T50 value and movement artefacts to be easily identified. They also allow rapid assessment of the distribution of T50 values in the lungs which may be particularly useful in segmental lung disease.