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Sarcoidosis has a wide spectrum of appearances within the thorax. This review will discuss and illustrate the range of pulmonary manifestations on high-resolution computed tomography and chest radiography, concentrating on atypical features and examples of sarcoidosis mimicking other lung diseases. All included cases have been histologically confirmed. Such variable imaging appearances should alert the radiologist to consider sarcoidosis as a differential diagnosis in the context of interstitial lung disease. [ABSTRACT FROM AUTHOR]

AIM: To assess the effect of changing from an 'appointment' to a 'same-day' ultrasound (US) service on referral pattern, departmental workload, and patient satisfaction. MATERIALS AND METHODS: To reduce US waiting time of 3 weeks for routine examinations, a 'same-day' service was started for outpatients and general practitioner (GP) patients in September 2006. To examine the effect of this change a retrospective assessment was performed of workload during 1 week in June 2006 (appointments only) and the same week in 2008, 22 months after the implementation of the new service. Distance travelled by patients and waiting time was recorded. Patient satisfaction with the service was assessed by questionnaire in September 2008. RESULTS: Hospital referrals remained stable, but GP referrals increased from 99 to 367 (270%) and distance travelled by patients increased from a median of 3.1 km (range 0.1-12.1 km) in 2006 to 4.8 km (range 0.2-19.8 km) in 2008 (p<0.001). Non-local GP referrals increased from 20/99 in 2006 (20%) to 198/367 in 2008 (54%). The increased workload was managed by flexible working by radiologists and two additional sonographers. Departmental waiting time increased for all patients with same-day patients waiting a median of 35 min (interquartile range 19-60 min). Ninety-one percent (79/87) of same-day patients rated the service excellent or good, but many requested better information on the waiting time. CONCLUSION: There is a demand from GPs for same-day US, and it is feasible in a large hospital with flexible radiology working and increased sonographic staffing. Unless adjacent hospitals offer a similar service, continuing rise in demand could overwhelm the service. [ABSTRACT FROM AUTHOR]

Aim: To investigate whether automated diameter assessment was feasible for CT colonography. Materials and Methods: Two experienced observers independently measured the maximum diameter of 50 polyps (colonoscopic reference size range 5-12 mm) from colonography datasets using conventionally placed software callipers and a variety of two-dimensional (2D) computed tomography (CT) window settings (colon, abdominal, bone, lung), and also three-dimensional (3D) perspective rendering. Polyps were also measured using automated polyp-segmentation software. Agreement between observers and with the colonoscopic reference measurement was determined using Bland-Altman, Wilcoxon, and Mann-Whitney U analyses. Results: Inter-observer agreement was similar for all window displays: mean difference in millimetres (SD difference; 95% limits of agreement) ranged from 0 (1.7, -3.3, 3.3) for 2D colon to -1.1mm (1.6, -4.3, 2.0) for 3D, compared with -0.5 (2.09, -4.6, 3.6) for automated measurement. When compared to colonoscopy, the largest discrepancy occurred using the 3D display (mean difference 1.3mm, 2.5mm for each observer). There was also a significant difference between estimates and reference size when using the 2D abdominal and 3D displays (p=0.03, <0.001). Conclusion: Automated polyp measurement is possible in vivo. Automated and conventional methods have comparable inter-observer agreement. The greatest measurement error is encountered when using a 3D display for estimates of diameter. [ABSTRACT FROM AUTHOR]

Purpose:  The FIGO score cannot accurately stratify low-risk gestational trophoblastic neoplasia (GTN) patients who develop chemoresistance to single agent methotrexate chemotherapy. Tumour vascularisation is a key risk factor and its quantification may provide non-invasive way of complementing risk assessment., Materials and Methods:  187 FIGO-staged, low-risk GTN patients were prospectively recruited. Power Doppler ultrasound was analysed using a quantification program. Four diagnostic indicators were obtained comprising the number of colour pixels (NCP), mean dB, power Doppler quantification (PDQ), and percentage of colour pixels (%CP). Each indicator performance was assessed to determine if they could distinguish the subset of low-risk patients who became chemoresistant., Results:  There were 111 non-resistant and 76 resistant patients. NCP performed best at distinguishing these two groups where the non-resistant group had an average 3435 (± 2060) pixels and the resistant group 6151 (± 3192) pixels (p < 0.001). PDQ and %CP showed significant differences (p < 0.001) but had poorer performance (area under ROC curves were 72 % and 67 % respectively compared with 75 % for NCP). The mean dB index was not significantly different (p = 0.133)., Conclusion:  Power Doppler ultrasound quantification shows potential for non-invasive assessment of tumour vascularity and can distinguish low-risk GTN patients who become chemoresistant from those who have an uncomplicated course with first line treatment., Competing Interests: Disclosure The authors report no conflicts of interest in this work., (© Georg Thieme Verlag KG Stuttgart · New York.)

Aim: To assess the effect on radiologist participation in learning from discrepancy meetings (LDMs) in a multisite radiology department by establishing virtual LDMs using OsiriX (Pixmeo)., Materials and Methods: Sets of anonymised discrepancy cases were added to an OsiriX database available for viewing on iMacs in all radiology reporting rooms. Radiologists were given a 3-week period to review the cases and send their feedback to the LDM convenor. Group learning points and consensus feedback were added to each case before it was moved to a permanent digital LDM library. Participation was recorded and compared with that from the previous 4 years of conventional LDMs. Radiologist feedback comparing the two types of LDM was collected using an anonymous online questionnaire., Results: Numbers of radiologists attending increased significantly from a mean of 12±2.9 for the conventional LDM to 32.7±7 for the virtual LDM (p<0.0001) and the percentage of radiologists achieving the UK standard of participation in at least 50% of LDMs annually rose from an average of 18% to 68%. The number of cases submitted per meeting rose significantly from an average of 11.1±3 for conventional LDMs to 15.9±5.9 for virtual LDMs (p<0.0097). Analysis of 35 returned questionnaires showed that radiologists welcomed being able to review cases at a time and place of their choosing and at their own pace., Conclusion: Introduction of virtual LDMs in a multisite radiology department improved radiologist participation in shared learning from radiological discrepancy and increased the number of submitted cases., (Copyright © 2016 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.)

Pulmonary arteriovenous malformations (PAVMs) are abnormal communications between the pulmonary arteries and veins, which result in a right-to-left (R-L) shunt with resultant hypoxemia, the severity of which will depend upon the size and number of lesions. Most PAVMs occur in individuals with hereditary haemorrhagic telangiectasia (HHT) and are a cause of serious morbidity and mortality largely related to cerebrovascular complications secondary to paradoxical embolization. The importance of their recognition and treatment by embolization, even in the absence of symptoms, is well known. Their appearances on chest radiographs are often, but not always, characteristic and the CT appearances are diagnostic; however, there are a number of both vascular and non-vascular diseases that can cause confusion. This review serves to highlight these PAVM "mimics"., (Copyright © 2014 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.)

The aim of this study is to investigate the effect of changing sphericity filter values on performance of a computer assisted detection (CAD) system for CT colonography for data with and without fecal tagging. Colonography data from 138 patients with 317 validated polyps were divided into those with (86) and without (52) fecal tagging. Polyp coordinates were established by three observers and datasets analysed subsequently by a proprietary CAD system used at four discrete sphericity filter settings. Prompts were compared with the known coordinates in order to determine sensitivity and specificity. Sensitivity was highest at low sphericity; of 164 polyps 6 mm or more, 144 (87.8%) were detected at sphericity 0.3, and 132 (80.1%) at sphericity 0.9. Of 42 polyps measuring 10 mm or more, 40 (95.2%) were detected at sphericity 0.3, and 36 (85.7%) at sphericity 0.9. There was no significant difference in sensitivity for tagged and un-tagged data but specificity was reduced in tagged data at low sphericity and significantly reduced in untagged data at high sphericity. CAD had a sensitivity of 95.2% for polyps measuring 1 cm or more and 87.8% for polyps 6 mm or more when used at a sphericity setting of 0.3. Higher sphericity settings increased specificity while reducing sensitivity. The bowel preparation used significantly impacts on specificity.

Purpose: To prospectively investigate the relative accuracy and reproducibility of manual and automated computer software measurements by using polyps of known size in a human colectomy specimen., Materials and Methods: Institutional review board approval was obtained for the study; written consent for use of the surgical specimen was obtained. A colectomy specimen containing 27 polyps from a 16-year-old male patient with familial adenomatous polyposis was insufflated, submerged in a container with solution, and scanned at four-section multi-detector row computed tomography (CT). A histopathologist measured the maximum dimension of all polyps in the opened specimen. Digital photographs and line drawings were produced to aid CT-histologic measurement correlation. A novice (radiographic technician) and an experienced (radiologist) observer independently estimated polyp diameter with three methods: manual two-dimensional (2D) and manual three-dimensional (3D) measurement with software calipers and automated measurement with software (automatic). Data were analyzed with paired t tests and Bland-Altman limits of agreement., Results: Seven polyps (

Aim: To externally validate a computer-assisted detection (CAD) system for computed tomography (CT) colonography, using data from a single centre uninvolved with the software development., Materials and Methods: Twenty-five multi-detector CT colonography examinations of patients with validated polyps accumulated at a single centre were examined by two readers who used endoscopic and histopathological data to identify polyp coordinates. A CAD system that had been developed using data from elsewhere, and had not previously encountered the present data, was then applied to the data at sphericity filter settings of 0.75 and 0.50 and identified potential polyps. True-positive, false-negative, and false-positive counts were determined by comparison with the known polyp coordinates., Results: Twenty-five patients had 57 polyps, median size 6mm (range 1-15mm). Per-patient sensitivity for the CAD system was 96% (24 of 25). The CAD system detected 44 (77%) polyps at sphericity setting 0.75 and 49 (86%) polyps at sphericity 0.50: the additional five polyps detected all measured 5mm or less. Sphericity of 0.75 resulted in a median of 10 (one to 34) easily dismissed false-positive prompts per patient and a median of 4 (zero to 15) that needed three-dimensional rendering before dismissal. This rose to 32 (16 to 99) and 11 (three to 35), respectively, at sphericity 0.5., Conclusions: A per-patient sensitivity of 96% was found for the CAD system (in patients with a median polyp diameter of 6mm) using external validation, a more stringent test than either internal cross-validation or temporal validation. Decreasing sphericity increases sensitivity for small polyps at the expense of decreased specificity.

Purpose: To retrospectively compare primary three-dimensional (3D) endoluminal analysis with primary two-dimensional (2D) transverse analysis supplemented by computer-assisted reader (CAR) software for computed tomographic (CT) polyp detection and reader reporting times., Materials and Methods: Ethical permission and patient consent were obtained from all donor institutions for use of CT colonography data sets. Twenty CT colonography data sets from 14 men (median age, 61 years; age range, 52-78 years) with 48 endoscopically proved polyps were selected. Polyp coordinates were documented in consensus by three unblinded radiologists to create a reference standard. Two radiologists read the data sets, which were randomized between primary 3D endoluminal views with 2D problem solving and 2D views supplemented by CAR software. Reading times and diagnostic confidence were documented. The CAR software highlighted possible polyps by superimposing circles on the 2D transverse images. Data sets were reread after 1 month by using the opposing analysis method. Detection rates were compared by using the McNemar test. Reporting times and diagnostic confidence were compared by using the paired t test and Mann-Whitney U test, respectively., Results: Mean sensitivity values for polyps measuring 1-5, 6-9, and 10 mm or larger were 14%, 53%, and 83%, respectively, for 2D CAR analysis and 16%, 53%, and 67%, respectively, for primary 3D analysis. Overall sensitivity values were 41% for 2D CAR analysis and 39% for primary 3D analysis (P=.77). Reader 1 detected more polyps than reader 2, particularly when using the 3D fly-through method (P=.002). Mean reading times were significantly longer with the 3D method (P=.001). Mean false-positive findings were 1.5 for 2D analysis and 5.5 for 3D analysis. Reader confidence was not significantly different between analysis methods (P=.42)., Conclusion: Two-dimensional CAR analysis is quicker and at least matches the sensitivity of primary 3D endoluminal analysis, with fewer false-positive findings., (Copyright (c) RSNA, 2006.)

Objective: The purpose of our study was to assess the sensitivity of computer-assisted reader (CAR) software for polyp detection compared with the performance of expert reviewers., Materials and Methods: A library of colonoscopically validated CT colonography cases were collated and separated into training and test sets according to the time of accrual. Training data sets were annotated in consensus by three expert radiologists who were aware of the colonoscopy report. A subset of 45 training cases containing 100 polyps underwent batch analysis using ColonCAR version 1.2 software to determine the optimum polyp enhancement filter settings for polyp detection. Twenty-five consecutive positive test data sets were subsequently interpreted individually by each expert, who was unaware of the endoscopy report, and before generation of the annotated reference via an unblinded consensus interpretation. ColonCAR version 1.2 software was applied to the test cases, at optimized polyp enhancement filter settings, to determine diagnostic performance. False-positive findings were classified according to importance., Results: The 25 test cases contained 32 nondiminutive polyps ranging from 6 to 35 mm in diameter. The ColonCAR version 1.2 software identified 26 (81%) of 32 polyps compared with an average sensitivity of 70% for the expert reviewers. Eleven (92%) of 12 polyps > or = 10 mm were detected by ColonCAR version 1.2. All polyps missed by experts 1 (n = 4) and 2 (n = 3) and 12 (86%) of 14 polyps missed by expert 3 were detected by ColonCAR version 1.2. The median number of false-positive highlights per case was 13, of which 91% were easily dismissed., Conclusion: ColonCAR version 1.2 is sensitive for polyp detection, with a clinically acceptable false-positive rate. ColonCAR version 1.2 has a synergistic effect to the reviewer alone, and its standalone performance may exceed even that of experts.

Objective: To investigate inter- and intraobserver agreement of automated measurement of polyp diameter in vitro., Methods: Two phantoms ("QRM" and "Whiting") containing simulated polyps of known diameter and volume were scanned using 16-detector row computed tomography. Two observers estimated polyp diameter using 3 methods: software calipers ("manual"), freehand boundary identification ("semiautomatic"), and automated software segmentation ("fully automatic")., Results: Intraobserver 95% limits of agreement for diameter were narrowest for the fully automatic method (QRM span: 0.39 mm, 0.48 mm; Whiting span: 0.24 mm, 0 mm). Manual estimates were approximately 10 times wider (QRM span: 3.57 mm, 3.21 mm; Whiting span: 3.2 mm, 2.02 mm). Volume estimates were narrowest for the fully automatic method (span: 24.2 mm, 24.1 mm vs. 97.9 mm, 102.9 mm for semiautomatic measurement). Interobserver agreement for diameter was narrowest for the fully automatic method (QRM span: 0.12 mm, Whiting span: 0.16 mm), with the manual method approximately 18 times wider (QRM span: 2.87 mm, Whiting span: 2.18 mm)., Conclusion: Fully automated measurement of polyp diameter and volume is technically feasible and results in superior inter- and intraobserver agreement.

Objective: The aim of this study was to define the relationship between interpleural distance measurements on an erect posteroanterior chest radiograph and pneumothorax size as measured by helical CT in a series of patients., Subjects and Methods: Twenty pneumothoraces from 19 patients (10 males, nine females) were analyzed. Most pneumothoraces were on the right side (n = 16). The etiology was spontaneous in seven patients and iatrogenic in thirteen. All patients underwent an erect inspiratory posteroanterior radiograph and a helical CT scan of the thorax on the same visit to the radiology department. The interpleural distance was measured at three locations and the figures added together. Following helical CT of the thorax, the percentage pneumothorax size was calculated by drawing regions of interest around the relevant hemithorax and lung on 10-mm reconstructed slices. A scattergram of the sum of interpleural distances in centimeters versus percentage pneumothorax size was plotted., Results: Analysis of results showed that percentage pneumothorax size could be calculated by the formula Y = 4.2 + [4.7 x (A + B + C)], r = .98, p < .0001., Conclusion: This study identified a formula for accurately calculating percentage pneumothorax size as determined by helical CT from an erect posteroanterior radiograph. Using this formula with the clinical status of the patient should more easily identify patients requiring active intervention.

Purpose: In this retrospective multicenter study, the authors analyzed the clinical efficacy of different metallic stents in the palliative treatment of patients with neoplastic obstructive jaundice., Patients and Methods: Two hundred forty patients were treated in four European centers. Causes of obstruction were pancreatic carcinoma (n = 84), biliary neoplasm (n = 99), metastases in hilar nodes (n = 34), primary or secondary liver tumors (n = 4), and other tumors (n = 19). A total of 388 metallic stents were used: 300 Wallstents, 35 nitinol Strecker stents, 40 Gianturco-Rosch Z stents, and 13 tantalum Strecker stents., Results: Overall 25- and 50-week survival rates were 42% and 16%, respectively; the 30-day mortality rate was 14.6%. Two deaths were related to the procedure (0.8%); 19 patients (8%) had major complications. The 25-week patency rate was significantly higher for the nitinol Strecker stents and the Wallstents (78% and 67%, respectively) than for the Z stents and the tantalum Strecker stents (30% and 20%, respectively) (P < .01 and P < .001, respectively). Average patency was 8.3, 5.9, 2.3, and 4.0 months, respectively. Reintervention due to stent obstruction was necessary in 53 patients., Conclusion: The Wallstent and the nitinol Strecker stents were the most effective in achieving long-term palliation. Patency was significantly affected by the level of obstruction but not by the type of obstructing tumor.

The development of self-expanding metallic endoprostheses which can be implanted easily, with minimal trauma, has revolutionized the non-surgical treatment of both benign and malignant biliary strictures. The Wallstent (Medinvent SA, Lausanne, Switzerland), a pliable, tubular stainless steel mesh, is the metallic stent of choice for treatment of malignant strictures and can be implanted in a single session resulting in a shortened hospital stay for patients undergoing palliation of irresectable biliary tumours. Although follow-up is currently rather limited, it appears that the occlusion rate of Wallstents will be lower than that of plastic endoprostheses and no cases of stent migration have been reported. The Gianturco zigzag stent (Cook Inc., Bloomington, Ind, USA) should not be used in malignant strictures because of rapid occlusion due to tumour ingrowth through the struts. However, it exerts a strong, continuous, outward radial force and is ideally suited for use in the small, but difficult to manage, group of patients with benign biliary strictures which recur despite surgery and repeated balloon dilations.

During a 28-month period, the authors placed 91 Wallstent endoprostheses in 55 patients with malignant obstructive jaundice. Five patients developed recurrent jaundice between 2 and 60 weeks after stent insertion due to stent occlusion by tumor overgrowth on seven occasions. To assess long-term segmental side-branch drainage through the walls of such endoprostheses, the cholangiograms obtained following stent occlusion were reviewed. In all five patients, evidence of drainage of intrahepatic ducts through the side of the mesh was observed. Although the number of patients in the series is small, this initial experience suggests that long metallic endoprostheses can be placed peripherally in the intrahepatic bile ducts without the potential risk of infection or occlusion of undrained, noninvolved segments. This policy may delay or prevent endoprosthesis occlusion in many patients.

Acute cholecystitis is a common condition which may be difficult to diagnose with confidence on clinical grounds alone. A large number of techniques are now available for imaging the gall bladder but, in practice, ultrasonography and cholescintigraphy are of greatest value. The former is cheap, readily available and features such as the presence of gall stones, gall bladder wall inflammation and a positive sonographic Murphy sign strongly suggest the diagnosis of acute cholecystitis. In addition to its diagnostic uses, ultrasonographically guided percutaneous cholecystostomy provides an alternative and sometimes life-saving form of treatment in those patients who are unfit for surgery. Cholescintigraphy is a highly accurate, non-invasive method for assessing patency of the cystic duct but is not always available in the emergency situation and takes longer to perform than an ultrasound examination. Acute cholecystitis, however, has many manifestations and may be calculous or acalculous, be associated with a patent or obstructed cystic duct, and may be complicated or uncomplicated. Imagining modalities other than those mentioned above may be useful in certain circumstances and this chapter aims to present the advantages and disadvantages of each technique in order to provide guidance for the clinician caring for a patient with suspected acute cholecystitis.

If a hypertensive patient with renal artery stenosis (RAS) is to benefit from percutaneous transluminal renal angioplasty (PTRA) in terms of a sustained improvement in blood pressure control, one may postulate a demonstrable reduction in renal blood flow (RBF) to that kidney, reversible by PTRA. In a population of 32 hypertensive patients, RAS was present in 23 of 62 kidneys. Eleven of the 32 patients underwent renal revascularization, of whom 6 showed improvement in blood pressure control at 6 mo, i.e., had renovascular hypertension (RVH). There was no correlation between RBF and angiographic appearances of the renal artery. Furthermore, there was no significant difference between RBF in the stenosed kidneys of the patients with RVH compared with the stenosed kidneys of patients without RVH. Individual kidney RBF was 22% (s.d. 11) higher 1-3 wk after PTRA but the increase did not correlate with clinical outcome. Angiotensin converting enzyme (ACE) inhibition increased RBF by 25% (s.d. 25) of baseline flow before PTRA but the increase did not correlate with clinical outcome. Measurement of RBF is of limited value for the prediction of the long-term blood pressure response following PTRA.

Duodenocaval fistula is exceedingly rare. Penetrating trauma, gunshot wounds and toothpick perforation of the duodenum are known aetiological factors. Two recent case reports have implicated radiation-induced ulceration of the duodenum. We describe the first case of duodenocaval fistula resulting from a giant peptic ulcer of the descending duodenum.

Symptoms caused by malignant hilar bile duct tumors are often palliated by the insertion of a percutaneous biliary endoprosthesis. However, these often occlude early and may be difficult to replace. We have reviewed our experience with percutaneous replacement of endoprostheses in 17 patients with 31 episodes of stent dysfunction. The stent was changed successfully in 30 of the 31 attempts. The average durations of initial and subsequent stent patencies were 28 and 20 weeks, respectively. Significant acute complications occurred in three patients, one of whom had a perihepatic abscess and two of whom had septicemia. Two patients died within 30 days of their last stent change. The one patient in whom attempted insertion of a new stent was unsuccessful had to remain on continuous external catheter drainage. The occluded or migrated endoprosthesis was successfully removed either percutaneously (55%) or endoscopically (26%) in 25 of the 31 cases. Successful removal of the stent and reinsertion after blockage or migration is possible in most patients. Our experience suggests that patients with malignant obstruction of the bile duct should not be refused an indwelling endoprosthesis just because of the frequent occurrence of early occlusion of the stent.

The use of 111In-labelled granulocyte scintigraphy is recognized as a reliable method for detecting osteomyelitis and has similar sensitivity and significantly increased specificity compared to bone scintigraphy and 67Ga studies. Recent published work using pure granulocytes labelled with 111In tropolonate to detect osteomyelitis resulted in sensitivity of 100% and specificity of 92%. 99Tcm as an alternative granulocyte label offers advantages of convenience, lower radiation dose and higher image resolution. We have scanned 20 patients with suspected osteomyelitis using autologous granulocytes labelled with 99Tcm hexamethylpropyleneamineoxime (HMPAO), 12 of whom had prosthetic joints. The scan results were correlated with clinical, radiographic, microbiological and histological findings. Sensitivity was 100% and specificity was 93% which compares favourably with results obtained using 111In-labelled granulocytes. We believe that labelled granulocyte scintigraphy is a useful investigation in the diagnosis of osteomyelitis and that 99Tcm HMPAO appears to be at least as useful as 111In as the labelling agent.

Leukocytes labeled with technetium-99m hexamethylpropyleneamine oxime (HMPAO) were used in 100 patients: 32 with suspected inflammatory bowel disease, 17 with fever of unknown origin, 21 with suspected abdominal sepsis, 20 with suspected bone sepsis, seven with bronchiectasis, and three with recent myocardial infarction. The distribution of activity in patients subsequently shown not to have inflammatory bowel disease was similar to that previously described for indium-111-labeled leukocytes. However, in this study, activity was also seen in the kidneys and bladder and occasionally the gallbladder on both early (1-3 hours) and late (24 hours) views, and in the colon in late views. Migration of Tc-99m-labeled granulocytes was seen in inflammatory disease as early as 30 minutes after injection, while normal bowel activity was not seen before 4 hours. The sensitivity of Tc99m-labeled leukocytes in the detection of inflammation was 100%, the specificity was 95%.

The lipophilic complex, 99Tcm-hexamethylpropyleneamine oxime (HMPAO) is an efficient leucocyte label, and labels granulocytes with more stability than mononuclear leucocytes. The recovery of 99Tcm-HMPAO granulocytes, expressed as the percentage of injected granulocyte-associated activity circulating as granulocyte-associated activity 40-45 min after injection, was 37% (S.E. 3%), similar to the recovery of 111In-labelled granulocytes isolated and labelled in plasma using tropolone. The T1/2 of 99Tcm-HMPAO labelled granulocytes in blood was 4.4 h (S.E. 0.4 h), less than that of 111In-labelled granulocytes, although when a correction was made for 99Tcm elution, it was 6.4 h. The initial biodistribution of 99Tcm-labelled leucocytes was similar to 111In-labelled granulocytes, with a rapid initial lung transit, prominent splenic activity, bone marrow activity and minimal hepatic activity, although, unlike 111In, 99Tcm activity was also seen in urine, occasionally in the gallbladder, and, from about 4 h, consistently in the colon. Bone marrow activity was particularly prominent with 99Tcm. About 6% of 99Tcm was excreted in the faeces up to 48 h after injection, and about 17% in urine up to 24 h. The time-activity curves of reticuloendothelial activity up to 24 h were broadly similar for the two labelled cell preparations, and the differences that were observed can be explained on the basis of a higher rate of 99Tcm elution. Clinical information given by the two agents was similar in 27 of 30 patients who received both. Of the three who gave different information, one received 111In-labelled granulocytes which were considered to be functionally suboptimal and two, with inflammatory bowel disease, showed different distributions of abnormal bowel activity. We conclude that with respect to granulocyte kinetics and clinical data, 99Tcm-HMPAO labelled leucocytes are comparable with 111In-tropolonate labelled granulocytes.