Medical Imaging Targeting Osteoblastic Bone Repair

MMI has recently acquired a GE SPECT/CT 670 PRO for all of its general nuclear medicine scans. It is a hybrid gamma camera that incorporates a diagnostic 16 slice CT scanner. Nuclear Medicine imaging procedures are a excellent tool for patient management. A bone scan for example is enhanced by this hybrid system to a highly specific diagnostic tool, far more sensitive than x-ray or even CT.

Gone are the days when nuclear medicine scans were referred to as “unclear medicine”. The sensitivity of nuclear medicine scans has never been in doubt however the ability to anatomically place pathology has been difficult, especially in joints of overlapping small bones. Wrists, ankles, knees and spine have previously been challenging areas for nuclear medicine in terms of specificity.

Standard x-ray or CT relies on changes in bone density to create an image. For example a fractured bone has lower density (thickness) along the line of the fracture. Indeed a space may be created once a bone cracks and in many cases a x-ray can find this space. However there is in many circumstances no space in the crack; the 2 parts have pressed back together with continued pain.

Arthritic conditions can also be challenging for x-ray or CT; easily found by these imaging modalities but unable to determine which joint is actively inflamed causing pain. Furthermore patients with previous surgical history or pathologies that present with new pain after successful intervention pose a challenge.

Bone scans target the actual process of bone regeneration. The gamma emitting radio-pharmaceutical is rich in phosphorus that chemically bonds on the surface of hydroxyapatite crystals. These hydrolze and bind normally to bone as tin oxide or TcO2. On the scan these present as prominent focal areas of osteoblastic activity. The Gamma camera builds an image over several minutes to visualise these areas of increased uptake as they emit gamma rays that collide with the gamma camera’s surface. A complete lack of uptake in bones suspected of injury is also of diagnostic value as it can detect vascular necrosis. Bone scans have also been used on patients that have undergone bone grafts to ascertain vascular perfusion of the new graft.

Bone scans are a sensitive imaging procedure that can identify inflamed facet joints in the spine. Once identified these joints can be treated by steroidal injections guided by CT. Bone scans are an excellent investigation for any patient experiencing ongoing bone or joint pain, or suspected sporting injuries that often are not seen on X-ray CT or MRI. The 16 slice diagnostic CT is highly important in bone scans as the fine slices can determine fractures from inflamed joints by fusing (overlaying) together the slices from the SPECT scan with those of the CT scan. The CT can also easily separate small overlapping bones in the ankles, feet, wrist, hand, cervical spine for accurate diagnosis.

These images are fused to incorporate the sensitivity of the bone scan with the accurate anatomy of the CT scan. This fusion technique allows clear visualisation and separation of prosthetic hardware from new areas of bone damage. Bone scans are also a easy way to determine spread of metastatic disease in patients with known cancer; particularly important when occult fracture is suspected.

Bone scans are also highly useful for elderly patients who are prone to falling. A whole body bone scan on an elderly patient who has pain in the lower back or pelvis after a fall would benefit from a bone scan. Insufficiency fractures in the sacro-iliac joint, fractures of the femoral neck and crush fractures in the spine are easily found on a bone scan. It is not uncommon to find other fractures whose symptoms are masked or unnoticed such as rib fractures in a whole body bone scan. That is a particular strength of bone scans; the one procedure can cover the entire skeletal system when searching for fractures post trauma.

Lists of clinical indications to obtain a bone scan for your patient:
– Detection of primary and staging metastatic disease.
– Detection of osteomyelitis
– Detection and evaluation of suspected infections, avascular necrosis, and prosthesis pain
– Evaluation of bone pain: trauma, occult fracture, metabolic bone disease
– Detection and evaluation of Paget’s disease
– Detection and evaluation of arthritis and joint disease
– Evaluation of bone graft viability, bone viability when infarction is in question.
– Evaluation of increased PSA pathology results
– Evaluation of neoplasm or known lesions
– Evaluation of response to chemotherapy, radiation therapy, antibiotic therapy and other treatment.
– Localisation of sites for biopsy.

Case1: Patient with previous surgery with prosthetic implants. Now presenting with new pain in both feet. Conclusion: In the delayed images in the left foot focal increased uptake is seen in the tibiotalar joint and associated with sclerosis and subchondral cyst formation. There has been previous surgery in the right foot with metal implants and with increased uptake in the talocalcaneal joint associated with arthritic change including sclerosis and subchondral change.

Case2: Patient presents with left heel pain and 1st metatarsal Conclusion: In the delayed study, there was mild focal uptake within the left medial sesamoid bone with an associated fracture. There was mildly increased uptake within the inferior aspect of the left calcaneum.

Case 3: Male patient presents with known Rheumatoid arthritis and worsening back pain. Conclusion: Increased uptake is seen at L5/S1 intervertebral disc consistent with degenerative disease. There is facet joint arthropathy at L3/4 bilaterally worse on the left and at L4/5 worse on the right. There is also some degenerative disease at L3/4.

Case 4: Patient presents with known breast cancer. Lower back pain for evaluation. Conclusion: SPECT images confirm uptake in the right L4/5 facet joint region, due to inflammatory degenerative change.

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