Bone scintigraphy equipped with a pinhole collimator for diagnosis of avascular necrosis of the femoral head

The pinhole: gateway to ultra-high-resolution three-dimensional radionuclide imaging

Today the majority of clinical molecular imaging procedures are carried out with single-photon emitters and gamma cameras, in planar mode and single-photon emission computed tomography (SPECT) mode. Thanks to the development of advanced multi-pinhole collimation technologies, SPECT imaging of small experimental animals is rapidly gaining in popularity. Whereas resolutions in routine clinical SPECT are typically larger than 1 cm (corresponding to >1,000 microl), it has recently proved possible to obtain spatial resolutions of about 0.35 mm ( approximately 0.04 microl) in the mouse. Meanwhile, SPECT systems that promise an even better performance are under construction. The new systems are able to monitor functions in even smaller structures of the mouse than was possible with dedicated small animal positron emission tomography ( approximately 1 mm resolution, corresponding to 1 microl). This paper provides a brief history of image formation with pinholes and explains the principles of pinhole imaging and pinhole tomography and the basics of modern image reconstruction methods required for such systems. Some recently introduced ultra-high-resolution small animal SPECT instruments are discussed and new avenues for improving system performance are explored. This may lead to many completely new biomedical applications. We also demonstrate that clinical SPECT systems with focussing pinhole gamma cameras will be able to produce images with a resolution that may become superior to that of PET for major clinical applications. A design study of a cardiac pinhole SPECT system indicates that the heart can be imaged an order of magnitude faster or with much more detail than is possible with currently used parallel-hole SPECT (e.g. 3-4 mm instead of approximately 8 mm system resolution).

Bone scintigraphy as a prognostic indicator for bone collapse in the early phases of femoral head osteonecrosis

OBJECTIVE

Destructive and reconstructive processes at the reactive interface in femoral head osteonecrosis (FHO) are not well defined or predictable. The objectives of our study were to analyze scintigraphic characteristics of the reactive interface in the early stages of FHO and to assess the prognostic value of the reactive interface on scintigraphy (SC).

METHODS

Thirty-six hips in 27 patients (21 men, 6 women; mean age 41 years, range 20 64 years) with a final diagnosis of radiographic stage 1 (4 hips) or stage 2 FHO (32 hips) were evaluated by planar and pinhole SC. Tracer uptake at the reactive interface on pinhole SC was assessed visually. Three categories were formed: normal, moderately increased, and highly increased activities. The time to head collapse was observed.

RESULTS

Tracer uptake at the reactive interface was more frequently increased in hips with stage 2 of the disease than in those with stage 1. In hips with the same stage of the disease, different activities were detected [stage 1 FHO: moderately increased in 1 of 4 (25%) and highly increased in 1 of 4 (25%0) hips; stage 2 FHO: moderately increased in 8 of 32 hips (25%) and highly increased in 20 of 32 (631%/) hips]. Femoral heads with highly increased activity at the reactive interface collapsed more frequently and earlier: 13/15 conservatively treated hips in stage 2 collapsed in 1-6 months, whereas no hips with normal uptake at the reactive interface collapsed in 12 months follow-up and only one of six hips with moderately increased activity collapsed after 11.5 months (P < 0.05).

CONCLUSION

Our results indicate that the tracer uptake at the reactive interface can be different in the same stage of FHO. High tracer uptake at the reactive interface in the early phases of FHO seems to be a bad prognostic sign for femoral head collapse.

Scintigraphy in rheumatic diseases

The aim of this review is to summarise the clinical role of nuclear medicine in rheumatology taking into consideration the most specific diagnostic applications and other worthwhile therapeutic contributions. Traditional bone scintigraphy and recent inflammation-targeting radiopharmaceuticals, such as radiolabelled leucocytes and immunoscintigraphy, now allow us to obtain highly sensitive total-body and tomographical imaging information that can be used for the diagnosis of osteoarticular disease. The most common extra-articular manifestations of rheumatic diseases due to digestive, central nervous, respiratory and cardiovascular system involvement can be diagnosed by specific scintigraphic methods. Radiosynovectomy plays an important role in providing effective treatment for some joint diseases that are resistant to pharmacological therapy. Diagnostic and therapeutic applications of nuclear medicine show the highest efficacy in the early phase of rheumatic diseases. In more advanced stages, scintigraphical techniques play a complementary role to radiographical investigations in the assessment of prognosis and therapy efficacy.

Unusual osteonecrosis of the femoral head misdiagnosed as a stress fracture

We report a case of femoral head osteonecrosis that originally was misdiagnosed as a femoral neck stress fracture by plain radiography and magnetic resonance imaging. The correct diagnosis was made using pinhole bone scintigraphy, which revealed a completely cold lesion of the entire femoral head, confirmed by histologic examination. The patient was treated with muscle pedicle bone grafting, and 3 months postoperatively, pinhole bone scintigraphy showed improved vascularity of the femoral head.

The role of single photon emission computed tomography in bone imaging

Single photon emission computed tomography (SPECT) of the bone is the second most frequently performed SPECT examination in routine nuclear medicine practice, with cardiac SPECT being the most frequent. Compared with planar scintigraphy, SPECT increases image contrast and improves lesion detection and localization. Studies have documented the unique diagnostic information provided by SPECT, particularly for avascular necrosis of the femoral head, in patients with back pain, for the differential diagnosis between malignant and benign spinal lesions, in the detection of metastatic cancer in the spine, for the diagnosis of temporomandibular joint internal derangement, and for the evaluation of acute and chronic knee pain. Although less rigorously documented, SPECT is being increasingly used in all types of situations that demand more precise anatomic localization of abnormal tracer uptake. The effectiveness of bone SPECT increases with the selection of the proper collimator, which allows one to acquire adequate counts and minimize the patient-to-detector distance. Low-energy, ultrahigh-resolution or high-resolution collimation is preferred over all-purpose collimators. Multihead gamma cameras can increase the counts obtained or shorten acquisition time, making SPECT acquisitions more practical in busy departments and also increasing image quality compared with single-head cameras. Iterative reconstruction, with the use of ordered subsets estimation maximization, provides better quality images than classical filtered back projection algorithms. Three-dimensional image analysis often aids lesion localization.