Survey on the use of pulmonary scintigraphy and angiography for suspected pulmonary thromboembolism in the UK

[Pulmonary embolism: the extent of computerized tomography]

The use of computerised tomography in the diagnosis of pulmonary embolism has been the subject of clinical research while, at the same time, technical progress has provided the current multidetector-row spiral equipment. Computerised tomography has been assessed both with respect to reference strategies as well as in extensive pragmatic trials. The preliminary evaluation of the clinical probability and the assay of d-dimers has progressively become imperative. The value of the venous doppler ultrasound of the legs, in particular in the elderly, is limited by the variable accessibility according to the centre. In rare cases, uncertainty persists, for example with a good quality negative multidetector-row spiral computerised tomography associated with a high clinical probability, leaving room for complementary explorations. The confrontation between clinicians and radiologists is then all the more pertinent.

Detection of Pulmonary Embolism Using 16-Slice Multidetector-Row Computed Tomography

OBJECTIVE

To compare different image reconstruction parameters for detecting emboli of the pulmonary arteries according to anatomic levels using 16-slice multidetector-row computed tomography in patients suspected of having an acute pulmonary embolism (PE).

METHODS

Sixty-two patients (33 male and 29 female) with a clinically suspected acute PE were included in the present study. Multidetector-row computed tomography scans were performed using 16-mmx0.75-mm collimation. Based on the computed tomography data set, different image reconstruction parameters were used for each patient: axial slice thicknesses (STs) of 0.75, 2, 4, and 6 mm; axial maximum intensity projection (MIP) STs of 4 mm; and coronal STs of 2 and 4 mm. In joint reading fashion, 2 experienced radiologists reviewed examination findings regarding the presence and/or absence of a PE. The reference standard for visualization and detection of PEs was defined using the axial images with a 0.75-mm ST.

RESULTS

In 23 of 62 patients, a PE was diagnosed. For main and lobar pulmonary arteries, the sensitivities and specificities were as follows: axial 2-mm images, 1.0/1.0; axial 4-mm images, 1.0/1.0; axial 6-mm images, 0.97/0.99; MIP 4-mm images, 0.95/0.99; coronal 2-mm images, 1.0/1.0; and coronal 4-mm images, 1.0/1.0. Regarding segmental and subsegmental pulmonary arteries, sensitivity and specificity varied: axial 2-mm images, 0.97/1.0; axial 4-mm images, 0.81/0.99; axial 6-mm images, 0.65/0.99; axial MIP 4-mm images, 0.63/0.99; coronal 2-mm images, 0.91/0.99; and coronal 4-mm images, 0.74/0.99.

CONCLUSIONS

In detecting segmental and subsegmental PEs, only the axial images with an ST of 2 mm proved to have results comparable with the axial 0.75-mm images. Therefore, thin-slice collimation and ST are mandatory for visualization of segmental and subsegmental PEs in patients suspected of having an acute PE.

MR angiography with sensitivity encoding (SENSE) for suspected pulmonary embolism: comparison with MDCT and ventilation-perfusion scintigraphy

OBJECTIVE

The aim of our study was to determine the utility of time-resolved contrast-enhanced MR angiography combined with sensitivity encoding (SENSE) for patients with pulmonary embolism. SUBJECTS AND METHODS. Forty-eight consecutive patients (26 men and 22 women; age range, 27-73 years; mean age, 55 years) with suspected pulmonary embolism underwent chest radiography, contrast-enhanced MDCT, MR angiography with SENSE, ventilation-perfusion scintigraphy, and pulmonary angiography. MR angiography with SENSE was performed using IV administration of gadolinium contrast medium with a 3D turbo field-echo pulse sequence (TR/TE, 4.0/1.2; flip angle, 30 degrees ) on a 1.5-T scanner. Capabilities of diagnosing pulmonary embolism using MR angiography (data set A), contrast-enhanced MDCT (data set B), contrast-enhanced MDCT with MR angiography (data set C), ventilation-perfusion scintigraphy (data set D), and contrast-enhanced MDCT with ventilation-perfusion scintigraphy (data set E) were determined by receiver operating characteristic analysis, using the results of pulmonary angiography as the reference standard. The diagnostic capability of each data set was analyzed on a per-vascular zone and a per-patient basis with the McNemar test.

RESULTS

Sensitivity and specificity of data set A were 83% and 97%, respectively, on a per-vascular zone basis and 92% and 94%, respectively, on a per-patient basis. Specificity and accuracy of data set A were significantly higher than those of data set D on a per-patient basis (p < 0.05).

CONCLUSION

Time-resolved MR angiography with SENSE is effective for the diagnosis of pulmonary embolism.

Diagnóstico por imagem do tromboembolismo pulmonar agudo

O diagnóstico do tromboembolismo pulmonar agudo é baseado na probabilidade clínica, uso do dímero D (quando disponível) e na avaliação por imagem. Os principais métodos de imagem utilizados no diagnóstico são representados por cintilografia ventilação-perfusão, angiografia pulmonar e tomografia computadorizada (TC). Na última década vários estudos têm demonstrado que a TC espiral apresenta elevada sensibilidade e especificidade no diagnóstico de tromboembolismo pulmonar agudo. Uma melhor avaliação das artérias pulmonares tornou-se possível com a recente introdução dos equipamentos de TC espirais com multidetectores. Vários pesquisadores têm sugerido que a angiografia pulmonar por TC espiral deve substituir a cintilografia na avaliação de pacientes com suspeita clinica de tromboembolismo pulmonar agudo. Os autores discutem os principais métodos de imagem utilizados no diagnóstico de tromboembolismo pulmonar agudo enfatizando o papel da TC espiral.

Helical CTPA in the investigation of pulmonary embolism: a 6-year review

AIM

To assess the change in practice and resulting diagnostic outcome in the radiological investigation of pulmonary embolism (PE) since the introduction of helical CTPA in a large teaching hospital.

MATERIALS AND METHODS

A retrospective review was undertaken of all radiological investigations performed over a 6-year period before and after the introduction of CTPA (protocols 1 and 2, respectively) as an integral part of the imaging protocol in the investigation of clinically suspected PE. The total numbers and results of all investigations are assessed for each protocol.

RESULTS

A substantial increase in both the total number of patients and the number of investigations performed for the investigation of PE since the introduction of CTPA occurred. Five hundred and twenty-six patients underwent 617 investigations in 1995-1996, and 760 patients underwent 805 investigations in 2001-2002. There was a significant decrease in the number of investigations per patient, 1.17 in 1995-1996 versus 1.06 in 2001-2002. Primary investigation showed a significant decrease in indeterminate examinations from 25.7 to 8.5% and an increase in positive results for PE from 18 to 24%.

CONCLUSION

In the study population there was a significant increase in the number of patients being investigated for PE, with a decrease in both the number of non-diagnostic investigations and the total investigations per patient since the introduction of helical CTPA. This is probably due to the ready availability of a new imaging technique and physicians awareness that CTPA has significantly improved specificity, which encourages the referral of patients for investigation.

Non-invasive diagnostic work-up of patients with clinically suspected pulmonary embolism; results of a management study

BACKGROUND

Clinicians often deviate from the recommended algorithm for the diagnosis of pulmonary embolism consisting of ventilation-perfusion scintigraphy and pulmonary angiography.

OBJECTIVES

To assess the safety and feasibility of a diagnostic algorithm which reduces the need for lung scintigraphy and avoids the use of angiography.

PATIENTS AND METHODS

Consecutive patients with a clinical suspicion of pulmonary embolism were prospectively investigated according to an algorithm in which the diagnosis of pulmonary embolism was excluded after a low clinical probability estimate and a normal d-dimer test result, a normal perfusion scintigraphy result, or a non-high probability scintigraphy result in combination with normal serial ultrasonography of the legs. In these patients anticoagulant treatment was withheld and they were followed up for 3 months to record possible thromboembolic events. During the study period, 923 consecutive patients were seen, of whom 292 were excluded because of predefined criteria.

RESULTS

Of the 631 included patients, the diagnosis was refuted on the basis of a low clinical probability estimate and a normal d-dimer test result (95 patients), normal perfusion scintigraphy (161 patients) and non-high probability lung scintigraphy followed by normal serial ultrasonography (210 patients). Of these 466 patients, venous thromboembolic complications during follow-up occurred in six (complication rate 1.3%, 95% confidence interval 0.5, 2.8). The diagnostic protocol was completed in 92% of all included patients.

CONCLUSION

The diagnosis of pulmonary embolism can be safely ruled out by a non-invasive algorithm consisting of d-dimer testing combined with a clinical probability estimate, lung scintigraphy, or serial ultrasonography of the legs (in case of non-diagnostic lung scintigraphy).

Major pulmonary embolism: review of a pathophysiologic approach to the golden hour of hemodynamically significant pulmonary embolism

Major pulmonary embolism (PE) results whenever the combination of embolism size and underlying cardiopulmonary status interact to produce hemodynamic instability. Physical findings and standard data crudely estimate the severity of the embolic event in patients without prior cardiopulmonary disease (CPD) but are unreliable indicators in patients with prior CPD. In either case, the presence of shock defines a threefold to sevenfold increase in mortality, with a majority of deaths occurring within 1 h of presentation. A rapid integration of historical information and physical findings with readily available laboratory data and a structured physiologic approach to diagnosis and resuscitation are necessary for optimal therapeutics in this "golden hour." Echocardiography is ideal because it is transportable, and is capable of differentiating shock states and recognizing the characteristic features of PE. Spiral CT scanning is evolving to replace angiography as a confirmatory study in this population. Thrombolytic therapy is acknowledged as the treatment of choice, with embolectomy reserved for those in whom thrombolysis is contraindicated.

Combined helical computed tomographic pulmonary angiography and lung perfusion scintigraphy for investigating acute pulmonary embolism

AIM

To evaluate a diagnostic protocol incorporating helical computed tomographic pulmonary angiography (CTPA) and lung perfusion scintigraphy in the detection or exclusion of pulmonary embolism (PE) in routine clinical practice.

MATERIALS AND METHODS

A prospective observational study of 808 consecutive patients with suspected acute PE was undertaken over a 23-month period. Twenty-nine cases who failed to follow the protocol were excluded, leaving 779 cases to be reviewed. The three main outcome measures were negative perfusion scintigraphy, positive CTPA and other significant abnormalities demonstrated on CT.

RESULTS

Two hundred and thirty-one (30%) had negative perfusion scintigraphy and no further investigation. CTPA was performed in 548 (70%) and PE confirmed in 193 (25% of all patients). Other significant abnormalities were demonstrated in 25 (3%). CTPA was technically inadequate in 15 (2%).

CONCLUSIONS

A confident conclusion was achieved in 449 cases (58%), with PE excluded in 231 (30%), proved in 193 (25%), and relevant alternative abnormalities found in 25 (3%). This protocol using both perfusion scintigraphy and CTPA is practical and more effective than either investigation alone.

The use of a D-dimer assay in patients undergoing CT pulmonary angiography for suspected pulmonary embolus

PURPOSE

To assess the ability of a semi-quantitative latex agglutination D-dimer test Accuclot with bedside measurements of arterial oxygen saturation, respiratory and cardiac rates to exclude pulmonary embolism (PE) on computed tomographic pulmonary angiography (CTPA).

MATERIALS AND METHODS

All patients referred to our CT unit for investigation of suspected acute pulmonary embolism were enrolled. Pulse oximetery, respiratory rate, heart rate and blood sampling for D-dimer testing were carried out just before CT. A high resolution CT (HRCT) of the chest was followed by a CT pulmonary angiogram (CTPA). The images were independently interpreted at a workstation with cine-paging and 2D reformation facilities by three consultant radiologists blinded to the clinical and laboratory data. If positive, the level of the most proximal embolus was recorded. Discordant imaging results were re-read collectively and consensus achieved.

RESULTS

A total of 101 patients were enrolled. The CTPA was positive for PE in 28/101 (28%). The D-dimer was positive in 65/101 (65%). Twenty-six patients had a positive CT and positive D-dimer, two a positive CT but negative D-dimer, 39 a negative CT and positive D-dimer, and 34 a negative CT and negative D-dimer. The negative predictive value of the Accuclot D-dimer test for excluding a pulmonary embolus on spiral CT was 0.94. Combining the D-dimer result with pulse oximetry (normal SaO2 > or = 90%) improved the negative predictive value to 0.97.

CONCLUSION

A negative Accuclot D-dimer assay proved highly predictive for a negative CT pulmonary angiogram in suspected acute pulmonary embolus. If this D-dimer assay were included in the diagnostic algorithm of these patients a negative D-dimer would have unnecessary CTPA rendered in 36% of patients.

The use of nuclear medicine techniques in the emergency department

Nuclear medicine techniques have received little attention in the practice of emergency medicine, yet radionuclide imaging can provide valuable and unique information in the management of acutely ill patients. In this review, emphasis is placed on the role of these techniques in patients with bone injuries, non-traumatic bone pain and in those with pleuritic chest pain. New developments such as single photon emission computed tomography (SPECT) in myocardial infarction are outlined and older techniques such as scrotal scintigraphy are reviewed. Radionuclide techniques are discussed in a clinical context and in relation to alternative imaging modalities or strategies that may be available to the emergency medicine physician. Aspects of a 24 hour nuclear medicine service are considered.

Diagnosing acute pulmonary embolism: effect of chronic obstructive pulmonary disease on the performance of D-dimer testing, ventilation/perfusion scintigraphy, spiral computed tomographic angiography, and conventional angiography. ANTELOPE Study Group. Advances in New Technologies Evaluating the Localization of Pulmonary Embolism

In patients with chronic obstructive pulmonary disease (COPD), differentiating a pulmonary embolism (PE) from an exacerbation of COPD can be difficult, since clinical signs and symptoms of the two conditions overlap. Development of reliable noninvasive or minimally invasive techniques for the diagnosis of PE is, especially in these patients, necessary. In this study we assessed the effect of COPD on the accuracy of the clinical probability estimate (CPE), spiral computed tomographic angiography (SCTA), D-dimer analysis, ventilation perfusion (V/Q) scintigraphy, and pulmonary angiography for the diagnosis of PE. From May 1997 through March 1998, 627 consecutive patients with suspected PE were investigated in six teaching hospitals. In these patients, D-dimer testing, CPE, V/Q scintigraphy, and SCTA and/or pulmonary angiography were performed according to a strict diagnostic protocol. The patients were also independently categorized as having COPD or not. A diagnosis of COPD was established in 91 patients (15%). The prevalence of PE was similar in patients with and without COPD (29% and 31%, respectively), notwithstanding the larger proportion of nondiagnostic V/Q scan results in patients with COPD (46% versus 21%, p < 0.001). The distribution of CPEs, diagnostic value of the D-dimer assay and SCTA, and reproducibility of pulmonary angiography were comparable among patients with and without COPD. The presence of COPD does not affect the diagnostic performance of CPE, D-dimer testing, SCTA, or pulmonary angiography. Furthermore, although more nondiagnostic V/Q scan results can be expected in the presence of COPD, V/Q scintigraphy remains a valuable screening test in patients with COPD.

Non-haemorrhagic obstetric shock

The causes of non-haemorrhagic obstetric shock (pulmonary thromboembolism, amniotic fluid embolism, acute uterine inversion and sepsis) are uncommon but responsible for the majority of maternal deaths in the developed world. Clinically suspected pulmonary thromboembolism should be treated initially with heparin and objective testing should be performed. If the diagnosis is confirmed, heparin is usually continued until delivery, following which anticoagulation in the puerperium is achieved with either warfarin or heparin. Amniotic fluid embolism is a rare complication of pregnancy, occurring most commonly during labour. The management of amniotic fluid embolism involves maternal oxygenation, the maintenance of cardiac output and blood pressure, and the management of any associated coagulopathy. Acute uterine inversion arises most commonly following mismanagement of the third stage of labour. The shock in uterine inversion is neurogenic in origin, although there may also be profound haemorrhage. The management of this condition includes maternal resuscitation and replacement of the uterus either manually, surgically or by hydrostatic pressure. Genital tract sepsis remains a significant cause of maternal death, the most common predisposing factor being prolonged rupture of the fetal membranes. The management of septic shock in pregnancy includes resuscitation, identification of the source of infection and alteration of the systemic inflammatory response.

Survey on the use of pulmonary scintigraphy, spiral CT and conventional pulmonary angiography for suspected pulmonary embolism in the British Isles

AIM

To determine current clinical practice in the radiological diagnosis of acute pulmonary embolism and assess the use of spiral volumetric computed tomography.

METHOD

A survey of 327 acute hospitals including cardiothoracic and orthopaedic tertiary referral centres was undertaken to assess current utilization of lung scintigraphy, spiral computed tomography and pulmonary angiography in the investigation of suspected pulmonary embolism. Responses were received from 215/327 (66%) centres.

RESULTS

Lung scintigraphy was provided by 208 hospitals (144 on-site and 64 off-site). Spiral CT services were provided by 111 (52%) hospitals (on- or off-site), 142 (66%) units had access to angiographic facilities. Sixty-three centres out of 215 (29%) offered both on-site lung scintigraphy and spiral CT while only 41/215 (19%) hospitals were able to undertake all three tests on-site. On average, 501 perfusion (Q) or ventilation-perfusion (V/Q) scintigrams were performed per hospital per year with 26 spiral CT studies and just 4.6 pulmonary angiograms.

CONCLUSION

These data suggest that lung scintigraphy is frequently the only imaging test in patients other than chest radiography, despite the large number of indeterminate results reported in most series.

Acute pulmonary embolism in patients with HIV disease

OBJECTIVES

To determine the incidence, mode of presentation, and outcome of pulmonary embolism (PE) in patients with HIV infection.

METHODS

Retrospective review of clinical case records, imaging department database, and necropsy reports of patients admitted to the specialist HIV/AIDS unit at UCL hospitals from April 1993 to August 1997 in order to identify those with a diagnosis of PE.

RESULTS

During the study period there were 3792 admissions of whom 10 (0.26%) had PE. All patients with PE presented with fever, seven were dyspnoeic, and seven had cough: all were thought initially to have respiratory infection. Only five patients had pleural pain. All 10 patients had abnormal baseline chest radiographs. The diagnosis in six was made by computed tomograph (CT) pulmonary angiography, in two was made by ventilation perfusion (V/Q) scanning, in one by both techniques, and in one at necropsy. CT angiography in addition to identifying thrombus also showed concomitant lung parenchymal abnormalities in all but one patient. Nine patients with PE had one or more risk factors for venous thromboembolism as did 34/40 case matched controls (odds ratio = 1.67; 95% confidence interval = 0.18-15.5). All patients diagnosed in life were anticoagulated and five survived.

CONCLUSIONS

PE was uncommon in this HIV infected population. The diagnosis should be considered in patients with respiratory infection which does not respond to antibiotics. Identifiable risk factors for venous thromboembolism appear to be unhelpful in increasing clinical index of suspicion for PE. As baseline chest radiographs are frequently abnormal, the diagnostic utility of V/Q scanning may be reduced and CT pulmonary angiography is the imaging modality of first choice.

Investigation and management of patients with pleuritic chest pain presenting to the accident and emergency department

The assessment of a patient with pleuritic chest pain calls for a high degree of clinical acumen and a high degree of suspicion that the diagnosis might be pulmonary embolism. This area is one of the most difficult in A&E medicine (and indeed chest medicine). One error is to "think the best" when considering the diagnosis in such patients but experience soon teaches to "think PE" and diagnose less serious conditions only when pulmonary embolism has been excluded. A key consideration is the presence of risk factors. Because the diagnosis is difficult, there should be no hesitation in requesting a senior opinion or referring to the inpatient medical team. We have produced an algorithm (fig 1) for the investigation and management of pleuritic chest pain as discussed in this article. Three questions relating to this article are: (1) Can pulmonary embolism be the diagnosis in a patient with pleuritic chest pain but a normal chest radiograph, ECG, and arterial blood gases? (2) What is the chest radiograph abnormality which is most likely to alert you to the possibility of pulmonary embolism? (3) What percentage of patients with a low clinical suspicion of pulmonary embolism but a high probability V/Q scan will have pulmonary embolism demonstrated on pulmonary angiography? The three key references are The PIOPED Investigators, Dalen, and Fennerty.

Diagnosis of pulmonary embolism by measurement of alveolar dead space

OBJECTIVE

Pulmonary embolism (PE) gives rise to alveolar dead space, which can be measured with a single breath test for CO2 (SBT-CO2). The characteristics of the SBT-CO2 are different in PE and other common conditions giving rise to alveolar dead space, notably airways disease. An analysis of alveolar dead space focusing on the late part of the breath (fDlate) has been suggested as a method for diagnosis of PE. Our aim was to evaluate this technique by comparison with lung scintigraphy.

METHODS

We randomly selected patients with clinical suspicion of PE. SBT-CO2 and lung scintigraphy were performed on the same day. The scintigraphies were reviewed and classified as high, intermediate and low probability of PE.

RESULTS

Out of 223 patients able to be evaluated, there were 20 of the high, 29 of the intermediate and 174 of the low probability category. There were large differences between the means of fDlate in the high and the intermediate and in the high and the low categories. We obtained a sensitivity of 85% and a specificity of 93% for diagnosis of PE, based on high and low probability categories. If a patient with previous PE, but no scintigraphic evidence of current PE, is excluded the sensitivity increases to 90%.

CONCLUSIONS

This study provides further support for the measurement of fDlate by the SBT-CO2 as a diagnostic test in patients with suspicion of PE. The test should be especially useful in small hospitals without access to pulmonary scintigraphy or pulmonary angiography.

Spiral computed tomographic scanning and magnetic resonance angiography for the diagnosis of pulmonary embolism

PURPOSE

To compare prospectively the accuracy of spiral computed tomography (CT) with that of ventilation-perfusion scintigraphy for diagnosing pulmonary embolism.

MATERIALS AND METHODS

Within 48 hours of presentation, 142 patients suspected of having pulmonary embolism underwent spiral CT, scintigraphy, and (when indicated) pulmonary angiography. Pulmonary angiography was attempted if interpretations of spiral CT scans and of scintigrams were discordant or indeterminate and intermediate-probability, respectively.

RESULTS

In the 139 patients who completed the study, interpretations of spiral CT scans and of scintigrams were concordant in 103 patients (29 with embolism, 74 without). In 20 patients, intermediate-probability scintigrams were interpreted (six with embolism at angiography, 14 without); diagnosis with spiral CT was correct in 16. Interpretations of spiral CT scans and those of scintigrams were discordant in 12 cases; diagnosis with spiral CT was correct in 11 cases and that with scintigraphy was correct in one. Spiral CT and scintigraphic scans of four patients with embolism did not show embolism. Sensitivities, specificities, and kappa values with spiral CT and scintigraphy were 87%, 95%, and 0.85 and 65%, 94%, and 0.61, respectively.

CONCLUSION

In cases of pulmonary embolism, sensitivity of spiral CT is greater than that of scintigraphy. Interobserver agreement is better with spiral CT.

Noninvasive diagnosis of suspected severe pulmonary embolism: transesophageal echocardiography vs spiral CT

OBJECTIVE

Patients with pulmonary embolism (PE) and echocardiographic signs of right ventricular overload have worse prognosis and may require aggressive therapy. Unequivocal confirmation of PE is required before thrombolysis or embolectomy. This study compares the value of transesophageal echocardiography (TEE) and spiral CT (sCT) in direct visualization of pulmonary artery thromboemboli in patients with suspected PE and echocardiographic signs of right ventricular overload.

MATERIAL AND METHODS

Forty-nine consecutive patients (29 men and 20 women), aged 52.2+/-18.3 years, with clinical suspicion of acute (23) or chronic (26) PE and otherwise unexplained right ventricular overload at transthoracic echocardiography underwent TEE and sCT. Main and lobar (central) pulmonary arteries were searched for emboli with both TEE and sCT, while segmental and subsegmental (distal) pulmonary arteries were searched only with sCT.

RESULTS

Of 40 patients with PE confirmed by high-probability lung scan (27) or angiography (13), central pulmonary arterial emboli were found at TEE and sCT in 32 (80%) and 36 (90%) patients, respectively. Neither method reported false central PE (specificity, 100%). When distal pulmonary arteries were analyzed, sensitivity of sCT increased to 97.5%, but three patients with primary pulmonary hypertension according to standard tests were misclassified as having distal PE (specificity, 90.1%). Most patients had bilateral PE according to sCT (34/36) and standard tests (40/40) but not TEE (15/32), probably due to its topographic limitations.

CONCLUSIONS

Because of high prevalence of bilateral central pulmonary thromboemboli in patients with hemodynamically significant PE, both sCT and TEE allow its definitive confirmation in most cases. Thrombi reported by sCT distally to lobar arteries should be interpreted with caution.

Magnetic resonance pulmonary angiography and direct imaging of embolus for the detection of pulmonary emboli

RATIONALE AND OBJECTIVES

The authors developed a two-dimensional breathhold magnetic resonance (MR) technique for the direct imaging of pulmonary emboli.

METHODS

In vitro MR imaging was performed to demonstrate the potential generation of clot-blood contrast by in vivo pulmonary embolism (PE). A two-dimensional magnetization prepared gradient-echo (turbo-FLASH) breathhold technique was designed to directly image intravascular emboli by the selective nulling of the blood signal. A turbo-FLASH pulmonary angiographic breathhold sequence was used to provide spatial localization of detected emboli. Thirteen patients with suspected PE were studied; 6 patients underwent conventional pulmonary angiography (CPA) and the remaining 7 had diagnoses based on findings from other studies.

RESULTS

In vitro study of blood clot demonstrated an initial rise and then fall in T1 sufficient to generate clot-blood contrast after eight days of clot formation. All patients with CPA or alternative study evidence of PE were diagnosed as positive with direct embolus imaging MR. There were no false-positive diagnoses. Three additional emboli were detected using the MR technique compared with CPA. The MR pulmonary angiographic sequence provided a useful road map for localization of intravascular emboli but was less sensitive for PE detection than the embolus imaging technique.

CONCLUSIONS

The direct imaging of PE is feasible using a simple two-dimensional breathhold technique.

Clinical utilization of the non-diagnostic lung scintigram

By virtue of the poor specificity of ventilation perfusion lung scintigraphy, a significant number of examinations for suspected pulmonary embolism (PE) result in a report which is neither normal nor high probability. These are unhelpful in establishing a firm clinical diagnosis. Patients with an indeterminate report should therefore undergo further investigation to establish the diagnosis particularly when treatment with anticoagulants is proposed. All lung scintigram reports issued over a 2-year period were reviewed and 102 indeterminate lung scintigram reports were identified. The case notes of 94 of these patients were examined and details of further investigation and management recorded. Fifty-one patients (55%) had no further radiological investigations and 19 (37%) of these were unequivocally categorized as having had pulmonary embolism by the referring clinician. Eighteen of these were treated with anticoagulation therapy. When patients proceeded to further radiological investigation then the result usually influenced the final clinical diagnosis. Clinicians frequently treat an intermediate report as the end point in investigation of suspected PE and consequently some patients may receive suboptimal management. By implementing a hospital wide policy of further investigation of non-diagnostic lung scintigrams, using a standard protocol, patient management could be improved.

V/Q defects and deep venous thrombosis following total hip replacement

Seventy-two patients undergoing elective total hip replacement were studied with bilateral venography, pre-operative and post-operative lung scans. Twelve belonged to a control group that received placebo injections and 60 patients to treatment groups that received low molecular weight heparin. The incidence of deep venous thrombosis was 11 (92%) of 12 patients in the control group and 18 (30%) of 60 patients in the treatment group (X2: P < 0.001). The incidence of pulmonary embolism (new unmatched perfusion defects) was five (42%) of the 12 patients in the control group and five (8.3%) of the 60 patients in the treatment groups (X2: P < 0.002). The incidence of pulmonary embolism (new unmatched perfusion defects) was eight (27.5%) of 29 patients with deep venous thrombosis and two (4.6%) of 43 without deep venous thrombosis (X2: P < 0.02). Of the ten patients who had pulmonary embolism according to this study's criteria (one or more new defect on perfusion, unmatched on the ventilation scan), eight would have been classified as high probability by the Biello criteria, and only five by the PIOPED criteria, if the pre-operative scans were not available. We conclude that having a pre-operative lung scan improves ability to interpret the postoperative lung scans in high risk patients.

The role of venous colour flow Doppler to aid the non-diagnostic lung scintigram for pulmonary embolism

Sixty patients admitted with a clinical diagnosis of pulmonary embolism underwent a prospective analysis of the value of lung ventilation/perfusion scintigraphy and lower limb colour flow venous Doppler. Twenty-two per cent of scintigrams gave a high probability of pulmonary embolus (PE) and 45% a low probability/normal. The remainder were classed as indeterminate scintigrams (33%) and of these, 55% showed leg thrombi on the ultrasound scan. These patients were therefore treated by anticoagulation. A small number of the low probability scintigrams also proved to have lower limb thrombi by ultrasound. As a result of these two investigations just over half of these patients with a clinical diagnosis of PE were anticoagulated (31 out of 60). In 62% of these the ultrasound suggested thrombi confined to the calf as a source of PE.

Pulmonary angiography and the diagnosis of pulmonary embolism

Pulmonary angiography is the definitive study for the identification of embolism. The development of accurate noninvasive methods for the detection of deep venous thrombosis has altered the indications for angiography. Many angiographic techniques have been developed, providing the opportunity to tailor the angiogram to the clinical situation of individual patients. Strict criteria must be used for interpretation of angiographic studies, and using state of the art equipment will diminish technically unsatisfactory examinations. CT and MR angiography will assume a significantly larger role in the identification of PE in the very near future. MR may become the method of choice, because it is the one noninvasive technique that shows promise for the study of both the deep venous system of the legs and pelvis and the pulmonary circulation.

Pulmonary scintigraphy in suspected pulmonary embolism: how often does it change clinical management?

The effect of pulmonary scintigraphy on patient management in suspected pulmonary embolism has been assessed in 158 patients. A change in management occurred in 30% following scintigraphy. The major effect was a reduction in the total number of patients who were anticoagulated. Heparin was stopped in 42 of the 74 patients to whom it had been administered prior to the scintigram.

99mTc-DTPA aerosol for same-day post-perfusion ventilation imaging: results of a multicentre study

A multicentre study was performed in an attempt to evaluate a submicronic technetium-99m diethylene triamine penta-acetic acid aerosol generated by a newly developed delivery system, the aerosol production equipment (APE nebulizer), for same-day post-perfusion ventilation imaging in patients with clinically suspected pulmonary embolism. Quantitative comparison between the DTPA aerosol and krypton gas demonstrated a close correlation with respect to regional pulmonary distribution of activity and peripheral lung penetration (n = 14, r = 0.94, P < 0.001 and r = 0.75, P < 0.0025, respectively). In 169 consecutive patients, DTPA aerosol images performed immediately following perfusion (inhalation scan I) were compared to those carried out on the next day (inhalation scan II) with respect to image quality and assessment of perfusion-ventilation matches or mismatches. Agreement between inhalation scans I and II with respect to perfusion defects matched or mismatched to ventilation was found in 166/169 (98%) studies. The image quality of inhalation scan I was equal to that of scan II in 72%; inhalation scan I was superior in 11% of cases, while scan II was superior in 17%. This submicronic 99mTc-labelled DTPA aerosol is well suited for fast same-day post-perfusion ventilation imaging in patients with clinical suspicion of pulmonary embolism.