Positron emission tomography/computed tomography: protocol issues and options

Combined positron emission tomography/computed tomography (PET/CT) became FDA-approved for clinical use in late 2001. There are several design advantages of combined PET/CT over PET and CT acquired on separate devices, including more accurate CT and PET data co-registration, improved lesion localization, consolidation of imaging studies, and reduced scan times compared to dedicated PET. There are several protocols that can used to scan patients on combined PET/CT devices. Although there is no single "correct" protocol for performing a PET/CT scan, the use of oral and intravenous contrast media may improve the diagnostic value of the CT component. Whether to utilize contrast media depends on important clinical variables, including the specific type of tumor and the likelihood of encountering viable abdominal and pelvic malignancy. This article discusses various protocols pertinent to PET/CT imaging, including how the CT portion of a PET/CT scan can be performed and optimized, as well as PET/CT interpretation and reporting issues.     

Three-dimensional computed tomography of the foot: optimizing the image

The complex anatomy of the foot can be imaged using high resolution computed tomography. High resolution serial nonoverlapping CT scans of foot anatomy have a high degree of soft tissue contrast, and excellent geometrical accuracy (no magnification error). Three-dimensional surface reconstruction from CT scans of the foot were performed using specially developed computer software. These surface reconstructions display the osseous and soft tissue anatomy of the foot in a form similar to anatomic preparations. The removal of overlying skin, disarticulation of the ankle, tarsals and metatarsals was accomplished using computer methods. Major factors necessary to optimize three-dimensional images are presented and illustrated. The technique has been applied in living subjects with arthritis, carpal coalitions, osteochondritis dissecans, and fractures. These images have been useful in communicating the findings on high resolution CT scans to referring clinicians, correlating CT findings in areas of complex anatomy, and eliminating overlying or obscuring structures by mathematically disarticulating the foot and individual tarsal bones.     

Aortic root abscess: multimodality imaging with computed tomography and gallium-67 citrate single-photon emission computed tomography/computed tomography hybrid imaging

Culture negative endocarditis and aortic root abscess can prove difficult diagnostic challenges. Computed tomography can be extremely useful in this setting. We report a case of an aortic root abscess 3 months after elective aortic valve replacement in which cardiac CT and hybrid imaging with Gallium-67 SPECT complemented workup with transesophageal echocardiography in establishing the diagnosis of an abscess.     

Finger fractures imaging: accuracy of cone-beam computed tomography and multislice computed tomography

Objective  

To compare the diagnostic accuracy and radiation exposure of cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) in the evaluation of finger fractures.     

Pancreatitis: computed tomography and magnetic resonance imaging

The value of CT in management of severe acute pancreatitis is well established. Some, but not all, experimental studies suggest a detrimental effect of intravenous iodinated contrast agents in acute pancreatitis, but although initial clinical data tends to support this, the positive advantages of enhanced CT outweigh the possible risks. Magnetic resonance imaging has been shown to be as effective as CT in demonstrating the presence and extent of pancreatic necrosis and fluid collections, and probably superior in indicating the suitability of such collections for percutaneous drainage. Image-guided intervention remains a key approach in the management of severely ill patients, and the indications, techniques and results of radiological intervention are reviewed herein. Both CT and MRI can be used to diagnose advanced chronic pancreatitis, with the recent addition of MRCP as a viable alternative to diagnostic endoscopic retrograde cholangiopancreatography (ERCP). Both MRCP and CT/MR imaging of the pancreatic parenchyma still have limitations in the recognition of the earliest changes of chronic pancreatitis – for which ERCP and tests of pancreatic function remain more sensitive – but the clinical significance of these minor changes remains contentious. Received: 12 February 1998; Revision received: 17 June 1998; Accepted: 22 June 1998     

Multislice computed tomography cardiac imaging: current status

Non-invasive CT coronary artery imaging has previously had little relevance to most UK radiologists due to the limited availability of electron beam CT scanners. Major advances in CT technology have promoted new applications for helical CT, which include cardiac imaging. Widespread installation of 'multislice' helical CT scanners will make CT coronary artery imaging available for the first time in many UK hospitals. The technical advances and early clinical trial data are reviewed and multislice helical CT cardiac imaging in general is discussed.     

Pictorial review: electron beam computed tomography and multislice spiral computed tomography for cardiac imaging

Electron beam computed tomography (EBCT) revolutionized cardiac imaging by combining a constant high temporal resolution with prospective ECG triggering. For years, EBCT was the primary technique for some non-invasive diagnostic cardiac procedures such as calcium scoring and non-invasive angiography of the coronary arteries. Multislice spiral computed tomography (MSCT) on the other hand significantly advanced cardiac imaging through high volume coverage, improved spatial resolution and retrospective ECG gating. This pictorial review will illustrate the basic differences between both modalities with special emphasis to their image quality. Several experimental and clinical examples demonstrate the strengths and limitations of both imaging modalities in an intraindividual comparison for a broad range of diagnostic applications such as coronary artery calcium scoring, coronary angiography including stent visualization as well as functional assessment of the cardiac ventricles and valves. In general, our examples indicate that EBCT suffers from a number of shortcomings such as limited spatial resolution and a low contrast-to-noise ratio. Thus, EBCT should now only be used in selected cases where a constant high temporal resolution is a crucial issue, such as dynamic (cine) imaging. Due to isotropic submillimeter spatial resolution and retrospective data selection MSCT seems to be the non-invasive method of choice for cardiac imaging in general, and for assessment of the coronary arteries in particular. However, technical developments are still needed to further improve the temporal resolution in MSCT and to reduce the substantial radiation exposure.     

Viability imaging by cardiac computed tomography

First-pass perfusion and delayed enhancement cardiac imaging have been shown to be feasible by cardiac CT. However, questions remain about its reliability, and ideal scanning parameters have yet to be fully established. In general, scar imaging with cardiac CT typically requires 2 scans, with first-pass perfusion information derived from the same data set used to visualize the coronary arteries. Reduced contrast enhancement on first-pass cardiac CT images represents reduced perfusion. Higher doses of contrast are required to perform viability imaging by cardiac CT. Approximately 10 minutes after contrast administration, viability information is obtained by performing a second (noncontrast) scan. In addition to the concepts of perfusion and viability imaging by cardiac CT, we review parameters such as scan timing, tube settings, contrast delivery, reconstruction, and postprocessing techniques, as well as the associated pitfalls and technical limitations in perfusion and viability imaging by cardiac CT.     

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.     

Bone tumors: magnetic resonance imaging versus computed tomography

The magnetic resonance (MR) imaging characteristics of bone tumors are described and the clinical utility of MR imaging in patient evaluation is reported. Fifty-two patients with skeletal lesions were examined with a Picker MR imager (0.15-T resistive magnet). Twenty-five patients had primary malignancies, seven had benign bone neoplasms, 15 had skeletal metastases, and five had neoplasm simulators. Forty-five patients had CT scans available for comparison. For demonstrating the extent of tumor in marrow, MR was superior to CT in 33% of cases, about equal to CT in 64%, and inferior to CT in 2%. For delineating the extent of tumor in soft tissue, MR was superior to CT in 38% of cases and about equal to CT in 62%. CT was superior in all cases for demonstrating calcific deposits and pathologic fractures. In four patients with metal prostheses or surgical clips, MR was superior to CT in documenting recurrent tumor because of artifactual degradation of the CT image. Direct sagittal and coronal images from MR permit accurate assessment of the relationship of tumor to adjacent normal structures, including the physis, joints, and neurovascular structures. MR is useful in the evaluation of bone tumors: it is of greatest value in evaluations of the peripheral skeleton, the medullary canal, soft tissues, and postoperative tumor recurrence. With a 0.15-T magnet, MR is less useful in the evaluation of the axial skeleton and cortical bone.     

Malignant hemangiopericytoma: computed tomography and magnetic resonance imaging

Computed tomography and magnetic resonance imaging of a malignant hemangiopericytoma in a 58-year-old woman are described. The tumor was initially found in the abdomen and resected 34 years ago, but recurred 18 years later, followed by repeated recurrence and eventually metastasis to the lung and then to the liver. The lung nodules were round or oval, homogeneous, and well circumscribed while the massive tumor in the right lobe of the liver was poorly delineated with irregular areas of cystic necrosis. With proper setting of the repetition time and echo delay, the metastatic tumor became distinct from the uninvolved hepatic tissue on magnetic resonance imaging. In this case computed tomography and magnetic resonance imaging were complementary in evaluation of such a tumor.     

Multi-detector row computed tomography: imaging the coronary arteries

Over the last 2 years, multi-detector row computed tomographic (MDCT) cardiac imaging has continued to rapidly develop and evolve from the experimental research setting to become a useful clinical tool. The increasing availability of MDCT presents today's clinicians with an additional non-invasive diagnostic cardiac imaging method, in particular for the coronary arteries. With the advent and increasing clinical use of 16-detector row machines, and now with the imminent clinical emergence of 64-channel machines, the improvements in spatial and temporal resolution and sophisticated ECG-gating are allowing motion-free, fast, accurate, detailed, contrast-enhanced cardiac imaging that begins to approach the accuracy of traditional invasive diagnostic techniques. Additional diagnostic information may also be provided.     

Rhabdomyolysis: magnetic resonance imaging and computed tomography findings

OBJECTIVE: Our purpose was to describe the magnetic resonance (MR) imaging and computed tomography (CT) findings in patients with rhabdomyolysis. METHODS: The medical records and imaging studies of 10 patients (5 males, 5 females; age range, 14-60 years; mean age, 28.3 years) with rhabdomyolysis were retrospectively reviewed. Magnetic resonance imaging was available in 9 patients and CT in 2 patients. RESULTS: Two distinct imaging types of rhabdomyolysis were observed. For type 1 rhabdomyolysis (n = 2), the affected muscles revealed homogeneously isointense to hyperintense on T1-weighted, homogeneously hyperintense on T2-weighted and short-tau inversion recovery (STIR) images, and homogeneously enhanced on contrast-enhanced MR images. For type 2 rhabdomyolysis (n = 8), the affected muscles revealed homogeneously or heterogeneously isointense to hyperintense on T1-weighted images, heterogeneously hyperintense on T2-weighted and STIR images, heterogeneously hypodense on CT images, and rim enhanced on contrast-enhanced MR and CT images with the presence of a specific presentation, named as the "stipple sign." CONCLUSIONS: Rhabdomyolysis is a clinical and biochemical syndrome comprising 2 distinct imaging types. Homogeneous signal changes and enhancement in the affected muscles advocate type 1 rhabdomyolysis. The stipple sign is helpful in demonstrating the areas of myonecrosis in type 2 rhabdomyolysis and, together with clinical and laboratory presentations, in reaching the correct diagnosis.     

Sacrococcygeal chordoma: magnetic resonance imaging and computed tomography

Magnetic resonance imaging (MRI) was compared to computed tomography (CT) in four cases of sacrococcygeal chordoma. Both techniques yielded important anatomic information and represented important advances over early radiologic imaging methods. MRI provides superior contrast with surrounding soft tissues because of the prolonged T1 and T2 times of the tumors. This was especially important in a case of recurrent chordoma. The direct sagittal images obtained by MRI were valuable in determining the extent of lesions. Either MRI or direct CT coronal images were needed for the demonstration of tumor involving the sacral nerve roots. It was not possible to reliably distinguish between tumor adherent to bowel wall and bowel wall invasion by either technique. It is concluded that MRI is at least equal to CT for demonstration of these lesions and seems likely to become the imaging method of choice.     

Limited cone-beam computed tomography imaging of the middle ear: a comparison with multislice helical computed tomography

Purpose: To determine the applicability of cone-beam computed tomography (CBCT) in otological imaging, and to compare its accuracy with the routinely used multislice helical CT (MSCT) for imaging of the middle- and inner-ear areas.

Material and Methods: Thirteen unoperated human cadaver temporal bones were imaged with CBCT and MSCT. Sixteen landmarks of the middle and adjacent inner ear were evaluated and compared for their conspicuity according to a modified Likert scale. Total scores and scores for subgroups including landmarks of specific clinical interest were also compared.

Results: No significant differences were found between the imaging techniques or subgroups when scores of individual structures were compared. While the middle ear itself was visible in all cases with CBCT, parts of the inner ear were “cut off” in four cases due to the limited field of view. For the same reason, the evaluation of the whole mastoid was not possible with CBCT. The cochlear and vestibular aqueducts were not visualized in either CT techniques. The contrast-to-noise ratio was more than 50% lower in CBCT than in MSCT, but still adequate for diagnostic task.

Conclusion: CBCT proved to be at least as accurate as routinely used MSCT in revealing the clinically and surgically important middle-ear structures. The results show that high-quality imaging of the middle ear is possible with the current CBCT device.