Introduction and Fundamentals of Pinhole Scintigraphy

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To those who acquired their anatomical knowledge of the skeleton with the aid of clean, dried bone specimens or a plastic mannequin it may appear as a mere inert weight-bearing scaffold of the human body. However, like all other organs, bone constantly undergoes remodeling and tubulation through the physiological and metabolic activities of osteoblasts and osteo-clasts. The principal role played by these bone cells is the maintenance of bone integrity and calcium homeostasis by balancing between the ratio of bone collagen production and resorp-

Hand Bone Cells
Fig. 1.1 One of the first radiographs of living human skeleton: anatomist Kolliker's hand, by Professor Röntgen in January 1896 at Würzburg University

tion and by governing mineralization processes. Collagen production is a histological property common to various connective tissues, but mineralization is unique to bone cells.

One of the first images of living human bone was a radiograph of the hand of the anatomist Kölliker taken by Wilhelm Conrad Röntgen at Würzburg University on 23 January 1896 (Fig. 1.1). Radiography then became the sole modality for visualizing the skeletal system in vivo, and it remained so until 1961 when Fleming and his coworkers produced the first

Fleming Bone Scan
Fig. 1.2A, B One of the first bone scans made with 85Sr. A Radiograph of forearm shows bone destruction due to metastasis in the proximal radius. B Dot photoscan reveals intense tracer uptake in the lesional area (from Fleming et al. 1961)

bone scintigraphic image using 85Sr, a gamma ray-emitting radionuclide (Fig. 1.2). Using bone scintigraphy they successfully diagnosed bone metastasis and fracture. Historically, the event marked the beginning of the clinical use of bone scintigraphy for diagnosing skeletal disorders. During the development stage, bone scintigraphy suffered from many problems, particularly the limited image quality and consequent low diagnostic specificity. But with the wide availability of high-technology gamma camera systems furnished with efficient detector-amplifier assemblies, high-resolution collimators including fine pinhole, refined software, and ideal radiopharmaceuticals such as 99mTc-labeled methylene diphosphonate (MDP) and 99mTc-labeled hydroxydiphosphonate (HDP), bone scanning has long become established as an indispensable nuclear imaging procedure. Bone scanning is highly valued for two major reasons: exquisite sensitivity and unique ability to assess metabolic, chemical, or molecular profile of diseased bones, joints, and even soft-tissue structures. The usefulness of nuclear bone imaging modalities have most recently been enriched by the advent of bone marrow scintigraphy and positron emission tomography (PET) or PET-CT, further expanding the already wide scope of nuclear bone imaging science.

Indeed, bone scintigraphy is recognized for its sensitivity in detecting bone metastasis weeks before radiographic change is apparent and even ahead of clinical signs and symptoms. Its usefulness has also been thoroughly tested in the diagnosis of covert fracture, occult trauma with enthesitis, contusion, transient or rheumatoid synovitis, early osteomyelitis and pyogenic arthritis, avascular osteonecrosis, and a number of other bone and joint diseases. The introduction of single photon computed tomography (SPECT) has significantly enhanced lesion detectability by enhancing the image contrast through slicing complex structure of the pelvis, hip, spine and skull. In addition, 67Ga citrate and mIn- or 99mTc -labeled granulocyte scans have made important contributions to the diagnosis of infective bone diseases. As an adjunct the quantification of bone scan changes has been proposed (Pitt and Sharp 1985), and data are now automatically processed. This analytical approach is based on the calculation of the activity ratios of bone to soft tissue, bone to bone, and bone to lesion. Measurement of bone clearance of 99mTc-MDP, photon absorptiometry, and quantitative bone scan are used increasingly in the study of osteoporosis and osteomalacia. Most recently, 18F FDG-PET has been shown to be a potent imaging method for the detection of not only the early primary cancers but also metastases to the bones, lymph nodes, and soft tissues (Abe et al. 2005; Buck et al. 2004).

In spite of unprecedented progress in computer technology, electronic engineering, and radiopharmaceuticals, the specificity of bone scintigraphic diagnosis has remained suboptimal and accordingly for more specific diagnosis of many bone and joint diseases additional information is still sought from radiography, CT, MRI and sonography, and finally such want has led to the hybridization of PET with CT. Silberstein and McAfee (1984) laboriously worked out a scintigraphic appraisal system to raise the specificity, but their success was partial. The factors counted on for scintigraphic diagnosis in the past were not specific morphological features that more or less directly reflected the pathological process in question, but included the following: increased or decreased tracer uptake, the number of lesions, unilaterality or bilaterality, homogeneity or not, and most problematically approximate anatomy. More essential determinants such as the size, shape, contour, accurate location, and internal texture of lesions cannot be portrayed by tracer uptake and distribution. Clearly, the reason for not analyzing more essential determinants was the relatively low resolution of the scan images made with multiple-hole collimators (O'Conner et al. 1991). This limitation remained unreme-died even after the introduction of SPECT. While SPECT is very effective for the elimination of the overlap of neighboring bones and significantly enhances contrast, the resolution remains unimproved. PET, a tomographic modality like SPECT, can sensitively indicate

Pinhole Collimator Bone Scan

Fig. 1.3 Spot scintigraphs (A-D) showing the difference in the grade of resolution among four scanning methods used for displaying a metastasis (arrows) in the transverse process of L3 vertebra. A LEAP collimator. B Blowup or computer zooming. C Geometric enlargement. D Pinhole magnification. The lesion can be localized specifically in the transverse process only by pinhole scintigraphy (D). E Anteroposterior radiograph shows osteolysis in the transverse process of the L3 vertebra (arrows)

Fig. 1.3 Spot scintigraphs (A-D) showing the difference in the grade of resolution among four scanning methods used for displaying a metastasis (arrows) in the transverse process of L3 vertebra. A LEAP collimator. B Blowup or computer zooming. C Geometric enlargement. D Pinhole magnification. The lesion can be localized specifically in the transverse process only by pinhole scintigraphy (D). E Anteroposterior radiograph shows osteolysis in the transverse process of the L3 vertebra (arrows)

Osteoporosis Vertebrae Rtg

where increased amounts of FDG are deposited in the cytoplasm of, for example, cancer cells. A PET scan alone, however, cannot identify exact anatomy, needing the help of CT in the form of PET-CT hybridization. It is evident that on the whole the interpretation of scintigraphy has traditionally relied on nonspecific or indirect findings.

Fortunately, pinhole bone scintigraphy can in greater detail display pathological changes in the individual disease of bones and joints as well as the soft tissues through an optical magnification with highly improved resolution. It must be remembered that mere blow-up, computer zooming or multihole collimator magnification does not truly enhance spatial resolution (Fig. 1.3). Pinhole scintigraphy appears ideal for establishing an improved piecemeal interpretation system at least for skeletal disorders. The level of spatial resolution and image contrast attained by pinhole scintigraphy has been shown to be of an order that is practically comparable to that of radiography both in normal and many pathological conditions (Bahk 1982, 1985, 1988, 1992; Bahk et al. 1987). For example, the small anatomical parts of a vertebra in adults and a hip joint in children can be distinctly discerned using this method. In an adult vertebra the pedicles, apophyseal joints, neural arches, and spinous process are clearly portrayed and in a pediatric (growing) hip the acetabulum, triradiate cartilage, capital femoral epiphysis and physis, and trochanters are regularly discerned (Chap. 4).

Clinically, pinhole scanningpermits differential diagnosis, for example, among metastases, compression fractures, and infections of the spine (Bahk et al. 1987). The "pansy flower" sign of costosternoclavicular hyperostosis, a pathognomonic "bumpy" appearance of the long bones in infantile cortical hyperostosis, and the "hotter spot within hot area" sign of the nidus of osteoid osteoma are just a few examples of diagnoses that can be made by observing characteristic or pathognomonic signs of the individual diseases (Bahk et al. 1992; Kim et al. 1992).

To summarize, it appears that, used along with the holistic physicochemical data derived from whole-body, triple-phase, and spot 99mTc-MDP bone scans, the detailed anatomicometa-bolic profiles of skeletal disorders portrayed by pinhole scintigraphy enormously enhance diagnostic feasibility. In addition, it is indeed worth reemphasizing that the diagnostic accuracy of pinhole scintigraphy can be greatly sharpened if the scintigraphs are read side-by-side with radiographs—the common royal road to all image interpretations (Fig. 1.3D, E).

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Responses

  • ulderico lettiere
    How does a SPECT Scan show bone damage?
    8 years ago
  • samuli
    What is pinhole scintigraphy?
    8 years ago
  • maximilian
    What are spots on a spect bone scan?
    8 years ago
  • Austin
    How to read a bone scan with SPECT?
    8 years ago

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