Imaging (out of print)

Changing healthcare needs require tomorrow's diagnostic imaging service providers to rapidly produce the highest quality of images, transmit them broadly, display them in alternative ways, and then archive and retrieve them efficiently. To accomplish this, digital radiographical image-capture systems become the critical part.

The promised benefits of digital radiography are numerous: faster availability of images, fewer repeat examinations, direct importation of patient identifiers from the radiology information system, compact storage, convenient retrieval, greater staff and clinician productivity and the potential for lower radiation doses.

Computed radiography (CR) technology based on storage phosphor plates is well established. The system is cheap, has good reproducibility, and is robust. The physical size of the units could be decreased and throughput increased, while increasing image quality. Increased detector properties and dual reading have made CR technology to a dose-efficient system. A high resolution 4×4 k matrix does not appear to offer general diagnostic improvement in chest applications compared with a 2×2 k matrix.

Direct radiography (DR) systems have been developed that convert X-ray signals into electric signals, either directly as in a selenium-based systems or indirectly as in the systems using a scintillator layer in combination with a-Si photodiodes. DR is the common name for a number of different technologies. The combination of high image quality with the potential for dose reduction represents a definite advantage of DR systems.

The selenium drum, as a dedicated chest unit, offers high image quality at a 400-speed acquisition dose; however, its role has declined since the advent of DR systems.

Currently it seems that hybrid solutions, in which both techniques, CR and DR, coexist, will probably remain prevalent in the foreseeable future.

Imaging plays a crucial role in the detection and management of patients with pneumonia. This present chapter discusses the different imaging methods used in the diagnosis and management of suspected pulmonary infections. The imaging examination should always begin with conventional radiography. When the results of routine radiography are inconclusive, computed tomography is mandatory. The combination of pattern recognition with knowledge of the clinical setting is the best approach to the pulmonary infectious process. A specific pattern of involvement can help suggest a likely diagnosis in many instances. In AIDS patients, diffuse ground-glass and interstitial infiltrates are most commonly present in Pneumocystis carinii pneumonia whereas in the nonimmonosupressed patients, a segmental lobar infiltrate is suggestive of a bacterial pneumonia. Round pneumonia is more often encountered in children than in adults and is most often caused by Streptoccocus pneumoniae. Different combinations of parenchymal and pleural abnormalities may be suggestive for additional diagnoses. When an infectious pulmonary process is suspected, knowledge of the varied radiographical manifestations will narrow the differential diagnosis, helping to direct additional diagnostic measures, and serving as an ideal tool for follow-up examinations.

The diagnosis of pulmonary embolism (PE) is difficult because the clinical presentation is nonspecific and no single diagnostic test is sensitive enough and specific enough to exclude or confirm clinically suspected PE.

Accurate clinical evaluation is the first and most important step to raise the suspicion of the disease and to set-up an appropriate diagnostic work-up. Several prospective studies have shown that pre-test clinical probability categorises patients into subgroups with different a prevalence for PE and that the positive and negative predictive value of various objective tests is strongly conditioned by the independently assessed pre-test clinical probability.

Perfusion, rather than ventilation/perfusion, scanning should be the pulmonary vascular imaging technique of first choice for the management of patients with suspected PE because of its high sensitivity and negative predictive value. The clinical usefulness of spiral computed tomographical pulmonary angiography (CPTA) in the diagnosis of PE has not, as yet, been firmly established, since its sensitivity ranges from 57–100%, and its specificity from 78–100%. Such wide ranges are likely to reflect differences in the patients studied, as well as in the technology used.

The diagnostic accuracy of CTPA in PE diagnosis is also dependent upon the location of emboli, since it is >90% for emboli involving central pulmonary vessels but decreases to much lower values for emboli confined to peripheral vessels. Recent and future technological developments of CTPA may greatly enhance the role of this technique in the diagnostic work-up of patients suspected of PE. The authors propose a noninvasive diagnostic strategy with high positive and negative predictive values, starting with a standardised assessment of clinical likelihood, followed by a perfusion lung scan and, eventually, by CTPA in patients with discordant clinical and scintigraphical findings.

Accurate diagnosis and quantification of pulmonary emphysema during life is important to understand the natural history of the disease, to assess the extent of the disease, and to evaluate and follow-up therapeutic interventions. Since pulmonary emphysema is defined on pathological criteria, new methods of diagnosis and quantification should be validated by comparisons against histological references. Recent studies have addressed the capability of computed tomography (CT) to accurately quantify pulmonary emphysema. These studies, overviewed in this article, have been based on CT scans obtained after deep inspiration or expiration, on subjective visual grading and on objective measurements of attenuation values by using dedicated softwares providing numerical data, on two-dimensional and on three-dimensional approaches, and compared CT data with pulmonary function tests. More recently, textural analyses were applied on CT scans to assess the presence, the extent, and the types of emphysema.

Quantitative CT has already been used in patient selection for surgical treatment of pulmonary emphysema and in pharmaco-therapeutical trials. However, despite numerous and extensive studies already available, this technique has not yet been standardised and important questions about how to best use the CT for the quantification of pulmonary emphysema are still unsolved.

The management of lung disorders, as a consequence of collagen vascular disorder, is often difficult. Clinical evaluation alone will not detect or characterise the nature of lung involvement in many cases. Furthermore, the physiological profile in patients with collagen vascular disease may be complex, since pathological processes with opposing physiological effects often coexist.

Histopathological examination of lung biopsy specimens in individual patients is notstraightforward because of issues of classification, observer variation between pathologists, and the multiplicity of pathological processes that can occur. Imaging studies are central to the management of patients with suspected lung disease in association with connective tissue disorders. In this regard, computed tomography (CT) has a central role; the sensitivity and accuracy of CT is higher than that of plain chest radiography. CT may also provide valuable clues about the morphological basis of sometimes complex lung pathology.

Computed tomography (CT) stays the routine imaging procedure for staging patients with nonsmall cell lung cancer because this technique provides the most detailed imaging information of the tumour and its extent. However, despite its high and continuously improving image quality, there are still a lot of cases where CT is not able to predict a correct tumour, metastases and node stage. Magnetic resonance imaging (MRI) may then be used, but MRI is not always able to solve the problem. Doing a positron emission tomography (PET) scan in addition to the CT examination is, at the present moment, probably the best way to perform TNM staging. This technique is especially valuable for mediastinal lymph node staging because it has a high negative predictive value meaning that a negative PET provides a >90% certainty of the absence of mediastinal lymph node metastases and justifies the ability to skip invasive diagnostic procedures and go directly to therapeutic surgery. Further studies are necessary, but it can be expected that PET can also be valuable during T-staging to differentiate between tumour and peritumoural atelectasis and inflammation. However, despite the fact that combining PET and CT improves the accuracy of mediastinal staging, very often a tissue diagnosis remains necessary. Mediastinoscopy is still generally considered the standard of care, although, newer minimally invasive biopsy techniques, such as transbronchial needle aspiration performed during bronchoscopy and especially endoscopic ultrasound with fine needle aspiration biopsy, receive increased attention in the literature. Most authors agree that an investigation for distant metastases should be started when the patient has signs and symptoms that might be caused by metastatic disease and when the patient has a primary tumour requiring extensive surgery. However, the approach to the detection of occult metastases remains controversial, both in terms of when to search and the optimal technique that should be used. PET can probably be important here also.

Interventional radiology is a technique based medical specialty, using all available imaging modalities (fluoroscopy, ultrasound, computed tomography: CT, magnetic resonance, angiography) for guidance of interventional techniques for diagnostic or therapeutic purposes. Actually, percutaneous transthoracic needle biopsy includes core needle biopsy besides fine needle aspiration. Any pleural, pulmonary or mediastinal fluid or gas collection is amenable to percutaneous pulmonary catheter drainage. Different energy modes can be used for transthoracic needle treatment of thoracic malignancies. Treatment of haemoptysis of bronchial artery or pulmonary artery origin, transcatheter embolisation of pulmonary arteriovenous malformations and pseudoaneurysms, angioplasty and stenting of the superior vena caval system and percutaneous foreign body retrieval are well established routine procedures, precluding unnecessary surgery. These techniques are safe and effective in experienced hands. CT is helpful in pre- and post-operative imaging of patients being considered for endobronchial stenting. Many procedures can be performed on an outpatient basis, thus increasing cost effectiveness of radiologically guided interventions in the thorax.

Traditionally, radiology of the lung was focused on imaging of structure, whereas only nuclear medicine provided a kind of functional assessment. New developments in magnetic resonance imaging (MRI) have opened up the field of functional imaging of ventilation. These techniques consist of administration of hyperpolarised noble gases, in particular helium-3 (³He), as well as oxygen, at different concentrations as tracer gases. Such studies predominantly provide regional details on gas distribution which can be assessed in a single breath-hold (ventilation defects) or dynamically (distribution kinetics) by ³He MRI or after averaging of multiple breaths (distribution defects) by oxygen-enhanced proton MRI. Additionally, investigations of oxygen uptake are feasible by both techniques, providing a complementary indirect assessment of pulmonary perfusion at the same time. Dedicated techniques also enable a novel approach to the characterisation of pulmonary microstructure. These new techniques have been applied in multiple preliminary studies especially: chronic airway disease, which have demonstrated a very high sensitivity for the detection of ventilation defects superior to computed tomography; nuclear medicine; or pulmonary function testing. With the introduction of standardised procedures, good reproducibility has been achieved. Together with quantifiable results these technique will now be applied to the detection and monitoring of the effects of drugs, e.g. bronchodilators. However, the specificity of ventilation MRI for a particular diagnosis is low. The assessment of clinical utility in chronic airway disease, chronic obstructive pulmonary disease, asthma, cystic fibrosis and bronchiolitis obliterans, is still ongoing.