Positron emission tomography scanning is coming to a hospital near you soon!

Positron emission tomography (PET) is still generally not available in the UK; however, there are plans to introduce a national service in England from April 2008. Plans are also at an advanced stage in Scotland and Wales. The main uses of PET are in preoperative staging of lung cancer, detection of recurrent colorectal cancer, and management of patients with lymphoma. Although these provide the bulk of the referral base, PET is also of use in specific situations in patients with less common cancers, such as head and neck cancer, gynaecological cancer, and melanoma. In its more common uses, PET has been shown to be cost effective. Positron emission tomography will play an increasing role in the evaluation of response to treatment to enable early separation of patients who are responding well to chemotherapy from those who are not responding and need to be transferred to another therapy.

Does inhalation of pentamidine in the supine position increase deposition in the upper part of the lung?

To assess the effect of posture on the distribution of nebulized pentamidine isethionate deposition in the lung, ten patients with AIDS were studied. Two nebulizer systems, System 22 Mizer (MedicAid) and Respirgard II (Marquest) were modified by adding 40 cm of corrugated tubing (volume 150 ml) to allow the patients to be studied in both the sitting and supine posture. Modification of the nebulizers caused a reduction in lung deposition in the sitting position for the System 22 Mizer but increased deposition in the Respirgard II compared with the unmodified apparatus. The ratio of upper to lower zone deposition (corrected for 133Xe distribution) was increased in the supine position for both devices (p less than 0.01). The best upper zone deposition was achieved with the unmodified System 22 Mizer in the sitting position. Respirgard II had the lowest nonpulmonary deposition and the lowest incidence of adverse effects. The supine position was associated with a redistribution of deposition to the upper zones. To attempt to reduce upper zone recurrence of Pneumocystis carinii pneumonia, the supine posture is suggested for less efficient nebulizer devices, ie, the Respirgard II, but for more efficient systems, ie, System 22 Mizer, the sitting position is probably suitable. This postulate needs to be confirmed by a clinical trial.

The place of lung 99mTc DTPA aerosol transfer in the investigation of lung infections in HIV positive patients.

Pneumocystis carinii pneumonia (PCP) is the most common cause of pneumonia in HIV antibody positive patients, but other pneumonias remain important, i.e. streptococcal and mycobacterial infections. A definitive diagnosis relies on obtaining samples from the lung either noninvasively (induced sputum), or invasively (bronchoalveolar lavage, transbronchial or open lung biopsy). We have used the noninvasive technique of nebulized 99mTc DTPA transfer, to assess patients with PCP (n = 30) and other lung infections (n = 20) to see whether this test will distinguish between the various infections. The presence of a biphasic, rapid transfer curve indicates severe extensive alveolar damage and is seen in PCP or legionella pneumonia. The mean transfer time (T50 +/- SEM) for patients with PCP (whether smokers or nonsmokers) was 2.1 +/- 0.2 min, and for two of the patients with legionella 3.2 min. In PCP effective treatment causes the transfer to slow (mean T50 22.7 +/- 3.3 min, n = 24) and become monoexponential. Other causes of these changes in transfer are discussed. The other pneumonias (streptococcal, mycobacterial, and staphylococcal) did not result in biphasic curves or very rapid times, their T50 values are indistinguishable from cigarette smokers. In this patient group the DTPA transfer is a useful noninvasive investigation with a very rapid, biphasic curve indicating a high probability of PCP.

Parenteral acyclovir therapy for cytomegalovirus infection after renal transplantation.

Three patients who had received cadaveric renal transplants developed fevers within three months of transplantation. Concurrent cytomegalovirus infection was confirmed by virological studies. In all three patients there was both a clinical and virological response to a five day course of intravenous acyclovir. In one patient the dose required to produce this response was 5 mg/kg/day; however two patients required 10 mg/kg/day. All three patients remain well after 8-12 months follow-up.

Incidence and significance of rising blood acetate levels during hemodialysis.

Recent work suggests that rising arterial acetate levels occur in some patients undergoing hemodialysis and that they may be responsible for some dialysis problems, particularly cardiovascular instability. Blood acetate levels and acetate flux rates have been determined in 20 adult and 4 pediatric patients during hemodialysis as well as in 4 patients with combined renal and hepatic failure. Rising acetate levels occurred in 25% of the adult patients, although they were stable in the children and the patients with renal and hepatic failure. The occurrence of hypotension during dialysis was unrelated to a high blood acetate level.

Misinterpretation of the upper parathyroid adenoma on thallium-201/technetium-99m subtraction scintigraphy.

Pre-operative thallium-technetium subtraction scintigraphy of 50 patients with primary hyperparathyroidism, which was subsequently proven on histology to be due to an adenoma, was compared with operative findings. Six scans were negative and seven uninterpretable. Of the remaining 37 patients, 34 had correct scan prediction of the anatomical locations of the adenomas. On examination of the origins of the adenomas, all six scintigraphic predictions of upper adenomas corresponded to tumours arising from the upper gland found at operation. Of the 25 lower predictions, there was one false positive and 16 were correct, i.e. of lower gland origin, but eight were found to originate from the upper gland. This misinterpretation is though to be due to the prolapse of an adenoma arising from the upper gland towards the lower pole of the thyroid, thereby mimicking a lower lesion on the scan.

Nuclear medicine and AIDS.

The human immunodeficiency virus (HIV) infection and its associated illnesses in a relatively young population of patients provides an expanding role for nuclear medicine. The disease enforces a review of each department's infection control procedures. It also necessitates a widening of the differential diagnosis in high risk patients. It has also resulted in an increase in the number of patients presenting with diseases such as Pneumocystis carinii pneumonia, Kaposi's sarcoma etc. which prior to the HIV epidemic were extremely rare. Thus in high risk patients the interpretation of abnormalities in nuclear medicine scans needs to include the spectrum of opportunistic infections and unusual tumours. The presence of opportunistic infections in the severely immunocompromised patient has lead to the development of techniques not normally used, i.e. lung 99Tcm-diethylenetriamine pentaacetate (DTPA) transfer/clearance, donor leukocyte scanning to allow rapid diagnosis of an abnormality. Radionuclide techniques are also used to monitor the effect of therapy directed at the HIV itself or against opportunistic infections. This review covers aspects of infection control as well as the use of radionuclides to investigate specific problems related to HIV infection and therapy of the associated disease processes.

Time for abstention from caffeine before an adenosine myocardial perfusion scan.

Seventy patients undergoing adenosine myocardial perfusion scintigraphy were studied. All patients reported abstention from products containing caffeine in the 12 h prior to the test. Blood samples were drawn prior to initiation of the stress test, and serum caffeine levels were determined using high-performance liquid chromatography. All patients were also asked about their coffee and tea drinking habits. Seventy-four percent of patients had measurable serum caffeine levels (n = 52) ranging from 0.1 to 8.8 mg.l-1. Results were correlated with maximum pulse rate, systolic and diastolic blood pressure changes and clinical symptoms during the test. There was no correlation between coffee or tea drinking habits and serum caffeine levels. A serum caffeine level of 2.9 mg.l-1 was considered a cut-off point for comparing patients. No significant difference was seen in mean maximum change of pulse rate, systolic and diastolic blood pressure between patients with serum caffeine levels > or = 2.9 mg.l-1 and those with lower serum caffeine levels. Of eight patients with serum caffeine levels > or = 2.9 mg.l-1, six had no symptoms (75%). When patients were classified as patients with no symptoms or patients with symptoms (mild, moderate or severe), a significant difference was demonstrated between patients with serum caffeine levels > or = 2.9 mg.l-1 and those with lower levels. This suggests 12 h abstention from caffeine may be insufficient. Whether this translates into false-negative perfusion scans should be the subject of a larger study.

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.

Cerebral perfusion deficits in divers with neurological decompression illness.

Cerebral perfusion deficits detected by injection of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) and single photon emission tomography is said to correlate well with clinical findings in divers with neurological decompression illness. We studied 12 divers. Six had residual cerebral signs (group 1) and six had no residual cerebral symptoms or signs (group 2). Perfusion deficits were as common in group 2 as in group 1. The site of the deficit did not correlate well with either the neurological findings at presentation or the residual clinical signs after treatment. The data suggest that claims that HMPAO scanning correlates with clinical findings and can be used for patients management were incorrect.

The effect of varying type and volume of sedimenting agents on leukocyte harvesting and labelling in sickle cell patients.

Leukocyte labelling in patients with sickle cell anaemia has been reported as difficult if not impossible due to the slow erythrocyte sedimentation rate (ESR) in these patients. This study investigated standard sedimentation methods in patients with sickle cell disease (n = 16) and compared the results obtained with those following changes in the amount and type of sedimenting agent used. Labelling with either 111In-oxine or 99Tcm-exametazime was attempted in only five patients. Replacement of the commonly used 6% Hetastarch (Hespan) with Dextran or Haemaccel did not improve leukocyte harvesting, even when the proportions used of these agents were increased. In most cases where standard procedures for leukocyte collection did not lead to harvesting of viable samples, it was possible to obtain adequate leukocyte labelling in the majority of sickle cell patients using a minor modification of standard techniques. In this group of patients a ratio of 8 ml of Hespan to 16 ml of blood should be used for cell separation. If this fails then donor cells, anti-granulocyte antibody labelling or HIG should be considered.

A one-hour walk-in service for wrist trauma imaging.

We investigated the feasibility of rapid imaging of wrist trauma following casualty presentation and any subsequent effect on image quality and interpretability. All patients referred for wrist imaging were injected with 370 MBq 99Tcm-hydroxymethyl diphosphonate (HDP) and imaged 1, 2 and 3 h later. Palmar images were acquired on a 256 x 256 x 16 matrix using a high-resolution collimator, 140 keV photopeak and a 20% window. The images were scored qualitatively by four qualified observers in three categories: image quality, lesion detection and lesion localization. Statistical analysis indicated a significant improvement in scan quality with time, the mean difference (+/- standard error of the mean) between the 1 and 3 h scans being 0.81 +/- 0.07 (P = 0.001). No significant differences were seen in lesion detection (0.05 +/- 0.08; P = 0.51) or localization (0.14 +/- 0.08; P = 0.10). We conclude that imaging of wrist trauma is possible as early as 1 h post-injection of 99Tcm-HDP, although negative studies at 1 h require a 3 h image to maintain diagnostic accuracy.

Does 99Tcm human serum albumin alter the characteristics of nebulized pentamidine isethionate?

Nebulized pentamidine has been used as therapy for Pneumocystis carinii pneumonia. The lung dose delivered using different nebulizer systems and doses of pentamidine from 50-600 mg is unknown. To measure this a marker which does not alter the characteristics of the nebulized pentamidine solution must be found. We have assessed the aerosol characteristics of four jet nebulizers (System 22, System 22 Mizer, Optimist, Respigard II) and one ultrasonic device (Pulmosonic) using two concentrations of pentamidine isethionate (50 mg and 300 mg) in 3 ml of solution. The jet nebulizers were operated at a flow rate of 6 l min-1, a rate suitable for home use. These measurements were repeated with 99Tcm labelled human serum albumin (HSA) added to the solutions. A linear relationship between 99Tcm-HSA activity and pentamidine concentration was demonstrated by using a nine stage cascade impactor. The Respigard II and Optimist produced the best results in terms of particle size (96% less than 5 microns), but the addition of the tracer to the latter led to a smaller particle size range and a reduction in the amount of aerosol present at the mouthpiece. The Mizer system had 52% of particles less than 5 microns, the Pulmosonic 46%. The Respigard II had a total output of 8.7 mg for the 50 mg concentration and 30.9 mg for the 300 mg concentration. The System 22 produced corresponding outputs of 18.0 mg and 67.1 mg with 54% of the aerosol particles less than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

A survey of the role of the UK physicist in nuclear medicine: a report of a joint working group of the British Institute of Radiology, British Nuclear Medicine Society, and the Institute of Physics and Engineering in Medicine.

Guidelines for the provision of physics support to nuclear medicine were published in 1999 by a joint working group of the British Institute of Radiology, the British Nuclear Medicine Society, and the Institute of Physics and Engineering in Medicine. Following publication of the guidelines, a survey was conducted by the working group to gather data on the actual level of physicist support in UK hospitals of different types and on the activities undertaken by physicists. The data were collected in the 12 months following the publication of guidelines and cover different hospital models and seven UK regions. The results provide evidence that many of the smaller units - small teaching hospitals and, particularly, small district general hospitals - have insufficient physics support. Although, on average, there is good agreement between the guidelines and the survey data for medium and large district general hospitals, there is wide variation in the level of physics provision between hospitals delivering apparently similar services. This emphasizes the need for national guidelines, against which institutions may be bench-marked and which may be used as a recommendation for the staffing levels necessary to ensure services are delivered safely and standards are not compromised. The complexity and variety of workload is an important factor in determining the level of physics support. As services develop, it is vital that this aspect is recognized to ensure that appropriate resources are available for the required physics input, even if any new service represents only a modest clinical throughput in terms of patient numbers.

Disposition of nebulized pentamidine measured using the direct radiolabel 123I-iodopentamidine.

The pulmonary deposition of nebulized pentamidine (300 mg, Respirgard II nebulizer) was measured in seven human immunodeficiency virus (HIV)-positive men using a new radiopharmaceutical, 123I-iodopentamidine. Mean total pulmonary deposition was 15.3 mg or 5.1% of the initial nebulizer dose. Further studies in two of the patients showed that at 24 h, 87% of deposited 123I was retained in the lungs. Small amounts of activity (expressed as a percentage of the initial nebulizer activity) were also detected over the thyroid (0.4%), bladder (1%) and gut (0.7%). The ratio of 123I activity to pentamidine concentration was similar in the nebulizer solution and urine. These results suggest that 123I-pentamidine may be sufficiently stable in vivo to be used to study the biodistribution of inhaled and parenteral pentamidine in humans.

Is the skull view necessary in routine gamma camera bone scanning?

Bone scans were reviewed in 478 patients, 237 with carcinoma of the breast, 47 with carcinoma of the lung, 43 with carcinoma of the prostate, 56 with other malignancies and 95 in whom scans were performed for basic screening purposes. In only 11 of the scans reviewed were abnormalities of the skull alone observed and in only one of the 11 scans was the finding of an abnormality thought to be clinically useful. This study suggests that in patients with known malignant disease, the skull view adds little useful information. However, when performing bone scans for screening purposes, the skull view may well give helpful information.

Positive gallium-67 citrate uptake in a patient with polyostotic fibrous dysplasia.

Fibrous dysplasia is an uncommon bone condition with characteristic radiologic features. It is well known that there is increased uptake of Tc-99m hydroxymethylene diphosphonate (HMDP) and methylene diphosphonate (MDP) in fibrous dysplasia. There are no reports of uptake of Ga-67 citrate by fibrous dysplasia. A case is reported in which positive Ga-67 uptake was seen in a patient with polyostotic fibrous dysplasia.