Single-photon emission computed tomography/computed tomography in endocrinology

The introduction of fusion of functional and anatomical imaging modalities into the field of endocrinology led to a major breakthrough in diagnosis, staging, and follow-up of patients with endocrine tumors. The management of endocrine tumors is based on a wide variety of conventional techniques, including computed tomography, ultrasound, or magnetic resonance imaging, and on scintigraphic functional techniques, associated with unique uptake and transport mechanisms and with the presence of high density of membrane receptors on some of these tumors. Anatomical modalities provide accurate detection and localization of morphological abnormalities, whereas nuclear medicine studies reflect the pathophysiological status of the disease process. Lack of structural delineation and relatively low contrast hamper the precise anatomical localization of the abnormal functional findings in the presence of potential concurrent foci related to the physiological biodistribution of the radiotracer or to processes unrelated to the evaluated disease entity. The notion that anatomical high-resolution and functional imaging data act as complementary methods led to various combination techniques of these modalities. However, coregistration of the functional and anatomical data after the acquisition of the 2 imaging modalities on separate machines, in different sessions, fails to provide accurate alignment of data, and the mathematical modeling is too cumbersome to be used on a routine basis. In contrast, hybrid imaging devices of single-photon emission computed tomography/computed tomography in a single gantry enable the sequential acquisition of the two modalities, with subsequent merging of data into a composite image display. These hybrid studies have led to a revolution in the field of imaging, providing clinically relevant information that is not apparent on separate images. The present review evaluates the contribution of the integrated single-photon emission computed tomography/computed tomography technology to image analysis and management of patients with endocrine tumors.     

Single-photon emission computed tomography/computed tomography in abdominal diseases

Single-photon emission computed tomography (SPECT) studies of the abdominal region are established in conventional nuclear medicine because of their easy and large availability, even in the most peripheral hospitals. It is well known that SPECT imaging demonstrates function, rather than anatomy. It is useful in the diagnosis of various disorders because of its ability to detect changes caused by disease before identifiable anatomic correlates and clinical manifestations exist. However, SPECT data frequently need anatomic landmarks to precisely depict the site of a focus of abnormal tracer uptake and the structures containing normal activity; the fusion with morphological studies can furnish an anatomical map to scintigraphic findings. In the past, software-based fusion of independently performed SPECT and CT or magnetic resonance images have been demonstrated to be time consuming and not useful for routine clinical employment. The recent development of dual-modality integrated imaging systems, which provide SPECT and CT images in the same scanning session, with the acquired images co-registered by means of the hardware, has created a new scenario. The first data have been mainly reported in oncology patients and indicate that SPECT/CT is very useful because it is able to provide further information of clinical value in several cases. In SPECT studies of abdominal diseases, hybrid SPECT/CT can play a role in the differential diagnosis of hepatic hemangiomas located near vascular structures, in precisely detecting and localizing active splenic tissue caused by splenosis in splenectomy patients, in providing important information for therapy optimization in patients submitted to hepatic arterial perfusion scintigraphy, in accurately identifying the involved bowel segments in patients with inflammatory bowel diseases, and in correctly localizing the bleeding sites in patients with gastrointestinal bleeding.     

Single-photon emission computed tomography/computed tomography in brain tumors

Anatomic imaging procedures (computed tomography [CT] and magnetic resonance imaging [MRI]) have become essential tools for brain tumor assessment. Functional images (positron emission tomography [PET] and single-photon emission computed tomography [SPECT]) can provide additional information useful during the diagnostic workup to determine the degree of malignancy and as a substitute or guide for biopsy. After surgery and/or radiotherapy, nuclear medicine examinations are essential to assess persistence of tumor, to differentiate recurrence from radiation necrosis and gliosis, and to monitor the disease. The combination of functional images with anatomic ones is of the utmost importance for a full evaluation of these patients, which can be obtained by means of imaging fusion. Despite the fast-growing diffusion of PET, in most cases of brain tumors, SPECT studies are adequate and provide results that parallel those obtained with PET. The main limitation of SPECT imaging with brain tumor-seeking radiopharmaceuticals is the lack of precise anatomic details; this drawback is overcome by the fusion with morphological studies that provide an anatomic map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT or MRI demonstrated usefulness for brain tumor assessment, but this process is often time consuming and not practical for everyday nuclear medicine studies. The recent development of dual-modality integrated imaging systems, which allow the acquisition of SPECT and CT images in the same scanning session, and their co-registration by means of the hardware, has facilitated this process. In SPECT studies of brain tumors with various radiopharmaceuticals, fused images are helpful in providing the precise localization of neoplastic lesions, and in excluding the disease in sites of physiologic tracer uptake. This information is useful for optimizing diagnosis, therapy monitoring, and radiotherapy treatment planning, with a positive impact on patient management.     

Statistical parametric mapping in brain single photon computed emission tomography after carbon monoxide intoxication

The purpose of this retrospective study was to assess regional cerebral blood flow in patients after carbon monoxide intoxication by using brain single photon emission computed tomography and statistical parametric mapping. Eight patients with delayed neuropsychiatric sequelae and ten patients with no neuropsychiatric symptoms after carbon monoxide intoxication were studied with brain single photon emission tomography imaging with 99mTc-hexamethyl-propyleneamine oxime. Forty-four control subjects were also studied. We used the adjusted regional cerebral blood flow images in relative flow distribution (normalization of global cerebral blood flow for each subject to 50 ml x 100 g(-1) x min(-1) with proportional scaling) to compare these groups with statistical parametric mapping. Using this technique, significantly decreased regional cerebral blood flow was noted extensively in the bilateral frontal lobes as well as the bilateral insula and a part of the right temporal lobe in the patients with delayed neuropsychiatric sequelae as compared with normal volunteers (P< 0.005). In the patients with no neuropsychiatric symptoms, significantly decreased regional blood flow in the bilateral frontal lobes particularly on the left side was detected. There was a significantly decreased regional cerebral blood flow in the right frontal lobe and insula in the patients with delayed neuropsychiatric sequelae as compared to those with no neuropsychiatric sequelae. It is concluded that statistical parametric mapping is a useful technique for highlighting differences in regional cerebral blood flow in patients following carbon monoxide intoxication as compared with normal volunteers. The selectively reduced blood flow noted in this investigation supports the contention that the decrease following carbon monoxide intoxication may be prolonged and further worsen in the frontal lobe. In addition, the present study may help to clarify the characteristics of the pathophysiological alteration underlying delayed neuropsychiatric sequelae.     

Technological development and advances in single-photon emission computed tomography/computed tomography

Single-photon emission computed tomography/computed tomography (SPECT/CT) has emerged during the past decade as a means of correlating anatomical information from CT with functional information from SPECT. The integration of SPECT and CT in a single imaging device facilitates anatomical localization of the radiopharmaceutical to differentiate physiological uptake from that associated with disease and patient-specific attenuation correction to improve the visual quality and quantitative accuracy of the SPECT image. The first clinically available SPECT/CT systems performed emission-transmission imaging using a dual-headed SPECT camera and a low-power x-ray CT subsystem. Newer SPECT/CT systems are available with high-power CT subsystems suitable for detailed anatomical diagnosis, including CT coronary angiography and coronary calcification that can be correlated with myocardial perfusion measurements. The high-performance CT capabilities also offer the potential to improve compensation of partial volume errors for more accurate quantitation of radionuclide measurement of myocardial blood flow and other physiological processes and for radiation dosimetry for radionuclide therapy. In addition, new SPECT technologies are being developed that significantly improve the detection efficiency and spatial resolution for radionuclide imaging of small organs including the heart, brain, and breast, and therefore may provide new capabilities for SPECT/CT imaging in these important clinical applications.     

Gadolinium-enhanced computed tomography angiography in multi-detector row computed tomography: initial observations

Rationale and Objectives. The feasibility of using gadolinium contrast medium for computed tomography angiography (CTA) in multi-detector row computed tomography and the effect of contrast medium dilution was investigated.Materials and Methods. Three pigs were each scanned in multiple sessions with injections of non-dilute and dilute contrast medium at a dose of 0.3 mmol/kg body weight. Non-spiral dynamic scanning at a fixed mid-abdominal aortic level and thoracoabdominal CTA were performed.Results. The magnitude of peak aortic enhancement was not significantly different between dilute and non-dilute contrast medium injections (P = .88), but the former showed earlier enhancement (mean of 2.3 seconds sooner, P < .01) than the latter. CT angiography with gadolinium contrast medium showed much lower enhancement than iodine contrast medium, but small vessels were readily identifiable.Conclusion. Gadolinium contrast medium combined with multi-detector row computed tomography may provide clinically useful CTA. Dilution of contrast medium shortens the enhancement time but has little effect on the magnitude.     

Interventional computed tomography

Due to the development and refinement of computed tomography (CT), sonography, and interventional techniques, the field of interventional radiology has seen tremendous growth in recent years. In particular, the precise anatomic detail provided by CT and sonography has allowed percutaneous biopsies and abscess drainages to be performed safely and effectively. Percutaneous biopsies are now becoming the most common interventional radiographic procedures in many institutions. The usual indications for a biopsy are to determine the etiology of a mass, neoplasm, or inflammation, and to determine whether masses in known oncologic patients represent scarring or residual viable tumor. Accuracy rates for most percutaneous CT-directed biopsies are well over 90%, and the complication rate is very low. CT-directed percutaneous abscess drainages are also safe and effective and, in most cases, will be preferable to surgical drainage. The initial indications for percutaneous drainage (single, unilocular fluid collections) have been greatly expanded to include multiloculated collections, interloop abscesses, periappendiceal abscesses, and even percutaneous cholecystotomies. Biopsy and drainage procedures, together with their accuracy rates, indications and complications, are reviewed in this monograph.     

Quantitative computed tomography

Quantitative computed tomography (QCT) is an established technique for measuring bone mineral density (BMD) in the axial spine and peripheral skeleton (forearm, tibia). QCT can determine in three dimensions the true volumetric density (mg/cm 3) of trabecular or cortical bone at any skeletal site. However, because of the high responsiveness of spinal trabecular bone and its importance for vertebral strength, QCT has been principally employed to determine trabecular BMD in the vertebral body. QCT has been used for assessment of vertebral fracture risk, measurement of age-related bone loss, and follow-up of osteoporosis and other metabolic bone diseases. This article reviews the current capabilities of QCT at different skeletal sites and the recent technical developments, including volumetric acquisition.     

Quantitative computed tomography

Quantitative computed tomography (QCT) was introduced in the mid 1970s. The technique is most commonly applied to 2D slices in the lumbar spine to measure trabecular bone mineral density (BMD; mg/cm³). Although not as widely utilized as dual-energy X-ray absortiometry (DXA) QCT has some advantages when studying the skeleton (separate measures of cortical and trabecular BMD; measurement of volumetric, as opposed to ‘areal’ DXA-BMDa, so not size dependent; geometric and structural parameters obtained which contribute to bone strength). A limitation is that the World Health Organisation (WHO) definition of osteoporosis in terms of bone densitometry (T score ?2.5 or below using DXA) is not applicable. QCT can be performed on conventional body CT scanners, or at peripheral sites (radius, tibia) using smaller, less expensive dedicated peripheral CT scanners (pQCT). Although the ionising radiation dose of spinal QCT is higher than for DXA, the dose compares favorably with those of other radiographic procedures (spinal radiographs) performed in patients suspected of having osteoporosis. The radiation dose from peripheral QCT scanners is negligible. Technical developments in CT (spiral multi-detector CT; improved spatial resolution) allow rapid acquisition of 3D volume images which enable QCT to be applied to the clinically important site of the proximal femur, more sophisticated analysis of cortical and trabecular bone, the imaging of trabecular structure and the application of finite element analysis (FEA). Such research studies contribute importantly to the understanding of bone growth and development, the effect of disease and treatment on the skeleton and the biomechanics of bone strength and fracture.     

Coronal computed tomography

The authors describe a method of direct coronal computed tomography (CT) of the body for infants and children who are introduced onto the gantry in a lateral decubitus position transversely across the examination table. Scans are planned from a lateral scout view, with the number of coronal scans ranging from four to six. Images are more informative and detail is sharper than routine axial cuts with coronal reformations. This method is valuable in resolving complex problems related to disease adjacent to the diaphragm and can accurately demonstrate the extension and relation of lesions to neighboring structures.     

Positron emission tomography/computed tomography

Accurate anatomical localization of functional abnormalities obtained with the use of positron emission tomography (PET) is known to be problematic. Although tracers such as (18)F-fluorodeoxyglucose ((18)F-FDG) visualize certain normal anatomical structures, the spatial resolution is generally inadequate for accurate anatomic localization of pathology. Combining PET with a high-resolution anatomical imaging modality such as computed tomography (CT) can resolve the localization issue as long as the images from the two modalities are accurately coregistered. However, software-based registration techniques have difficulty accounting for differences in patient positioning and involuntary movement of internal organs, often necessitating labor-intensive nonlinear mapping that may not converge to a satisfactory result. Acquiring both CT and PET images in the same scanner obviates the need for software registration and routinely provides accurately aligned images of anatomy and function in a single scan. A CT scanner positioned in line with a PET scanner and with a common patient couch and operating console has provided a practical solution to anatomical and functional image registration. Axial translation of the couch between the 2 modalities enables both CT and PET data to be acquired during a single imaging session. In addition, the CT images can be used to generate essentially noiseless attenuation correction factors for the PET emission data. By minimizing patient movement between the CT and PET scans and accounting for the axial separation of the two modalities, accurately registered anatomical and functional images can be obtained. Since the introduction of the first PET/CT prototype more than 6 years ago, numerous patients with cancer have been scanned on commercial PET/CT devices worldwide. The commercial designs feature multidetector spiral CT and high-performance PET components. Experience has demonstrated an increased level of accuracy and confidence in the interpretation of the combined study as compared with studies acquired separately, particularly in distinguishing pathology from normal, physiologic tracer uptake and precisely localizing abnormal foci. Combined PET/CT scanners represent an important evolution in technology that has helped to bring molecular imaging to the forefront in cancer diagnosis, staging and therapy monitoring.     

Oxygen-assisted breath-holding in computed tomography

To achieve prolonged breath-holding, oxygen was administered just before dynamic CT and high resolution lung CT. Oxygen administration has proved to be a supportive means to improve the quality of CT studies.     

Single-photon emission computed tomography/computed tomography in lung cancer and malignant lymphoma

In nuclear oncology, despite the fast-growing diffusion of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET), single-photon emission computed tomography (SPECT) studies can still play an useful clinical role in several applications. The main limitation of SPECT imaging with tumor-seeking agents is the lack of the structural delineation of the pathologic processes they detect; this drawback sometimes renders SPECT interpretation difficult and can diminish its diagnostic accuracy. Fusion with morphological studies can overcome this limitation by giving an anatomical map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT images proved to be time-consuming and impractical for routine use. The recent development of dual-modality integrated imaging systems that provide functional (SPECT) and anatomical (CT) images in the same scanning session, with the acquired images coregistered by means of the hardware, has opened a new era in this field. The first reports indicate that SPECT/CT is very useful in cancer imaging because it is able to provide further information of clinical value in several cases. In SPECT, studies of lung cancer and malignant lymphomas using different radiopharmaceutical, hybrid images are of value in providing the correct localization of tumor sites, with a precise detection of the involved organs, and the definition of their functional status, and in allowing the exclusion of disease in sites of physiologic tracer uptake. Therefore, in lung cancer and lymphomas, hybrid SPECT/CT can play a role in the diagnosis of the primary tumor, in the staging of the disease, in the follow-up, in the monitoring of therapy, in the detection of recurrence, and in dosimetric estimations for target radionuclide therapy.     

Angiographic computed tomography is comparable to multislice computed tomography in lumbar myelographic imaging

We evaluated the feasibility of angiographic computed tomography (ACT) for diagnostic imaging in a patient with degenerative lumbar spine disease. ACT provides a volume data set out of a rotational acquisition with a c-arm-mounted flat-panel detector. Using this technique, radiographic myelography and myelographic computed tomography can be performed in a single session at the same imaging system. The quality of the reconstructed ACT slice images is comparable to those acquired by postmyelographic computed tomography.     

Cranial computed tomography in leukaemia

Summary The computed tomograms performed on a series of 41 patients during the course of prolonged treatment for acute leukaemia were reviewed. Thirty-one of these cases were referred for some neurological disturbance, the remainder for routine assessment. Abnormalities were present in 59%. In two cases there were leukaemic deposits, four were due to infection and four to necrotising leucoencephalopathy. Diffuse cerebral swelling occurred in three patients, and ventricular dilatation in 15, associated with enlarged cortical sulci in 13. The relationship of these findings to drug therapy is discussed.