**4.1 Radiolabelled leukocytes: Pharmacological and physiochemical characteristics**

These days radiolabelled leukocytes are the most commonly used method to detect and localize infection. The leukocytes can be labelled using either Indium-111 (In-111) oxyquinoline or Tc-99m hexamethylpropylene amine oxime (HMPAO). In-111 oxine is a highly lipophilic ligand which diffuses across leukocyte membranes. Once inside the cell, it dissociates into oxine (8-hydroxyquinoline, which diffuses out of the cell) while In-111 is retained within the cytoplasm as a result of binding with intracellular proteins. In-111 labelled leukocytes localize at sites of infection through diapedesis, chemotaxis, and enhanced vascular permeability. In-111 has a physical half-life of 67 hours. It decays by

Fig. 5. A 19-year old male referred for evaluation of pain left lower limb. Tc-99m MDP images show hyperaemia, increased pool activity and intense increase tracer uptake in the distal end of left tibia. SPECT/CT images show a well-defined low attenuation metaphyseal

lesion with central radiolucent area surrounded by peripheral bone sclerosis clearly

of osteomyelitis with features typical of a Brodie's Abscess.

**4. Radiolabelled leukocytes scintigraphy** 

confined to within the bone itself sparing the joint cavity. Findings consistent with diagnosis

**4.1 Radiolabelled leukocytes: Pharmacological and physiochemical characteristics**  These days radiolabelled leukocytes are the most commonly used method to detect and localize infection. The leukocytes can be labelled using either Indium-111 (In-111) oxyquinoline or Tc-99m hexamethylpropylene amine oxime (HMPAO). In-111 oxine is a highly lipophilic ligand which diffuses across leukocyte membranes. Once inside the cell, it dissociates into oxine (8-hydroxyquinoline, which diffuses out of the cell) while In-111 is retained within the cytoplasm as a result of binding with intracellular proteins. In-111 labelled leukocytes localize at sites of infection through diapedesis, chemotaxis, and enhanced vascular permeability. In-111 has a physical half-life of 67 hours. It decays by electron capture with gamma emissions of 173 and 247 KeV. In-111 labelled leukocytes are normally distributed to the liver, spleen, and bone marrow. Intense pulmonary activity is seen soon after injection, which clears rapidly, and it is probably due to leukocyte activation during labelling, which impedes their movement through the pulmonary vascular bed, prolonging their passage through the lungs.

Tc-99m HMPAO is a lipophilic agent that readily crosses the cell membrane of leukocytes. Once inside the cell the compound becomes hydrophilic and remains trapped. It is subsequently bound to intracellular organelles, primarily the nucleus and mitochondria. The bond to granulocytes is more stable than to monocytes and the tag elutes from these cells five times more rapidly. The normal biodistribution of Tc-99m HMPAO labeled leukocytes is more variable. In addition to the reticuloendothelial system, activity is also normally present in the genitourinary tract, large bowel, blood pool, and occasionally the gallbladder. Physiologic bowel excretion limits the usefulness of this agent for imaging abdominal infections.

#### **4.2 Radiolabelled leukocytes: Labeling technique**

There are a number of methods for labelling leukocytes, however, the basic principles and technique remains uniform. Approximately 40 ml of blood is withdrawn from the patient into a syringe that contains anticoagulant. This syringe containing blood is then kept in an upright position for about 1–2 hours to promote gravity erythrocyte sedimentation, a process that is facilitated by the addition of hydroxyethyl starch. The process can be accelerated by using hypotonic lysis of the red cells instead of gravity sedimentation as well. After the erythrocytes have been separated, the leukocytes must be separated from platelets. The leukocyte-rich plasma is centrifuged, and the leukocyte "pellet" that forms at the bottom of the tube is removed, incubated with the radiolabel, washed, and re-injected into the patient. The usual dose of In-111 labelled leukocytes is 10–18.5 MBq; while the routine dose of Tc-99m HMPAO labelled leukocytes is 185–370 MBq. The majority of leukocytes labelled are neutrophils, and hence the procedure is most useful for identifying neutrophil-mediated inflammatory processes, such as bacterial infections. The procedure is less useful in conditions where the predominant cellular response is other than neutrophilic such as tuberculosis.

A total white count of at least 2000/mm3 is needed to obtain satisfactory images. ABO compatible donor WBC's may be used in neutropenic patients (i.e. White cell count less than 2000/mm3). Radiolabelled leukocytes should be administered within 1–2 hours of cell labelling. Labelled cells stored longer than 3 hours have a significant loss of cell viability. Temperatures higher than 70°F tend to increase cell damage and should be avoided. Cell labelling should be performed by trained laboratory personnel in a laminar flow hood using sterile procedures. Care must be taken to ensure correct identification of patients and blood products. All patients and laboratory procedures should have an appropriate quality control program.

#### **4.3 Radiolabelled leukocytes: Imaging protocols and pre-requisites**

In-111 labelled leukocyte is usually performed 18-24 hours post injection because early imaging at 4 hours usually misses out on two-thirds of the lesions detected on later images. However, it is critical to obtain early (1-4 hour) images when evaluating patients for inflammatory bowel disease or those suspected of possible ischemic bowel disease.

Radionuclide Infection Imaging: Conventional to Hybrid 83

Fig. 6. A 30-year old female with chronic left leg pain, presented with tenderness and swelling at left lower leg. Tc-99m MDP bone scan show increased pool activity and increase tracer accumulation at the distal ½ of left fibula on delayed images. Tc-99m HMPAO labelled leukocytes scan showed increase tracer uptake in the distal left fibula

in detecting osteomyelitis in patients with prosthetic implants (Figure 7).

of osteomyelitis.

corresponding to the site seen on bone scan, findings consistent with scintigraphic evidence

Labelled leukocytes imaging have been used in the diagnosis of orthopaedic implant infection after positive findings on three phase bone scanning. False positive scans can occur due to dystrophic ossification, peri-prosthetic granulomas, altered distribution of red marrow, and damage to the polyethelene surface of the prosthesis and metallosis. Combined leukocyte-marrow imaging can overcome many of the problems created by variable marrow distribution post-operatively. (Palestro et al., 1990) reported good results with combined In-111 labelled leukocytes/bone marrow imaging, with 86–100% sensitivity and 97–100% specificity in hip and knee prosthesis infections. (Joseph et al., 2001) also noted the ability of added sulphur colloid scanning to eliminate the false positive results. Our own experience suggest Tc-99m HMPAO labelled leukocytes scan appears significantly valuable

Labelled leukocyte imaging is the procedure of choice for the evaluation of patients with diabetic foot. Sensitivity and specificity of In-111 labelled leukocytes for diabetic foot osteomyelitis is between 72%-100% and between 67%-100%, respectively. Sensitivity of Tc-99m HMPAO labelled leukocytes has been reported to be 90% and 93% while the specificity has been observed to be 86% and 100% by various groups. Interestingly, the combination of Tc-99m HMPAO labelled leukocytes scan with Tc-99m three phase bone scan has yielded both high sensitivity and high specificity (92.6% and 97.6%, respectively), moreover this combination is of benefit in patients with Charcot osteoarthropathy. The reported sensitivity

Occasionally, 48 hour delayed images may be necessary due to prolonged circulation of labelled cells in about 10% of cases. Limited spot views or whole body imaging can be acquired depending upon the clinical indication. Images should be acquired with a medium-energy parallel-hole collimator. Energy discrimination is accomplished by using a 15% window centered on the 173 KeV photopeak and a 20% window centered on the 247 KeV photopeak. Simultaneous In-111 leukocyte/Tc-99m MDP bone images can be obtained using a gamma camera that can acquire and discriminate the 140 KeV Tc-99m photons from the In-111 photons. Each In-111 leukocyte/Tc-99m bone image is acquired using a medium energy collimator for 50K counts in the In-111 window or for 15 minutes, 4 hours and/or 16–30 hours post injection of In-111 leukocytes. Tc-99m Sulphur colloid imaging can also performed after or simultaneously with In-111 leukocyte imaging if bone marrow distribution is in question.

The interval between injection of Tc-99m HMPAO labeled leukocytes and imaging varies with the indication; in general, imaging is usually performed 3-4 hours post injection. Some centers perform only 2 hours post injection images and occasionally 24 hour delayed images may be necessary due to prolonged circulation of labelled cells.

#### **4.4 Radiolabelled leukocytes: Clinical utilities and applications**

Labelled leukocytes have been used for the diagnosis of complicated osteomyelitis after fractures and surgery i.e. violated bone, vascular graft infections, and various soft-tissue insults. In-111 labelled leukocytes are probably the preferable agent for imaging suspected sites of infection in the abdomen, while Ga-67 is preferable for detecting pulmonary pathology in the setting of FUO. There are advantages as well as certain disadvantages associated with both In-111 and Tc-99m labelled leukocytes. Advantages of the In-111 label are those of virtually constant normal distribution of activity that is limited to the liver, spleen, and bone marrow and its more stable in-vivo characteristics. Further In-111 labelled leukocytes can be used in simultaneous dual-isotope acquisitions. On the contrary, the drawbacks of the In-111 label include a low photon flux due to less than ideal photon energies. When compared to the Tc-99m label, the latter has a high photon flux and somewhat ideal photon energies; with relatively more radioactivity injected, the ability to detect abnormalities within a few hours post injection is a plus for Tc-99m label. Disadvantages of Tc-99m labelled leukocytes include genitourinary tract activity, which appears shortly after injection, and colonic activity, that appears by 4 hours post injection thereby obscuring potential foci of infections at these sites.

Labelled leukocytes have been studied by many to be an accurate technique for the diagnosis of osteomyelitis in the setting of violated bones as well as in diabetic foot infection. The overall sensitivity and specificity of Tc-99m HMPAO labelled leukocytes is 88% and 91%, respectively, for osteomyelitis in previously violated bones. However, Tc99m HMPAO labelled leukocytes imaging is performed only after a positive finding on a three phase bone imaging, because the latter is highly sensitive but significantly less expensive, making it more appropriate as a first-line screening procedure. (Devillers et al., 2000) reported an overall sensitivity, specificity, and accuracy of 93%, 100%, and 96%, respectively, for Tc-99m HMPAO labelled leukocytes and 100%, 17%, and 53.3%, respectively, for Tc-99m MDP bone imaging. In our own experience combined Tc-99m HMPAO/Tc-99m MDP imaging proved useful in diagnosing osteomyelitis. The specificity of Tc-99m MDP bone scanning improved from 30% to 78% with the addition of Tc-99m HMPAO labelled leukocytes (Figure 6).

Occasionally, 48 hour delayed images may be necessary due to prolonged circulation of labelled cells in about 10% of cases. Limited spot views or whole body imaging can be acquired depending upon the clinical indication. Images should be acquired with a medium-energy parallel-hole collimator. Energy discrimination is accomplished by using a 15% window centered on the 173 KeV photopeak and a 20% window centered on the 247 KeV photopeak. Simultaneous In-111 leukocyte/Tc-99m MDP bone images can be obtained using a gamma camera that can acquire and discriminate the 140 KeV Tc-99m photons from the In-111 photons. Each In-111 leukocyte/Tc-99m bone image is acquired using a medium energy collimator for 50K counts in the In-111 window or for 15 minutes, 4 hours and/or 16–30 hours post injection of In-111 leukocytes. Tc-99m Sulphur colloid imaging can also performed after or simultaneously with In-111 leukocyte imaging if bone marrow

The interval between injection of Tc-99m HMPAO labeled leukocytes and imaging varies with the indication; in general, imaging is usually performed 3-4 hours post injection. Some centers perform only 2 hours post injection images and occasionally 24 hour delayed images

Labelled leukocytes have been used for the diagnosis of complicated osteomyelitis after fractures and surgery i.e. violated bone, vascular graft infections, and various soft-tissue insults. In-111 labelled leukocytes are probably the preferable agent for imaging suspected sites of infection in the abdomen, while Ga-67 is preferable for detecting pulmonary pathology in the setting of FUO. There are advantages as well as certain disadvantages associated with both In-111 and Tc-99m labelled leukocytes. Advantages of the In-111 label are those of virtually constant normal distribution of activity that is limited to the liver, spleen, and bone marrow and its more stable in-vivo characteristics. Further In-111 labelled leukocytes can be used in simultaneous dual-isotope acquisitions. On the contrary, the drawbacks of the In-111 label include a low photon flux due to less than ideal photon energies. When compared to the Tc-99m label, the latter has a high photon flux and somewhat ideal photon energies; with relatively more radioactivity injected, the ability to detect abnormalities within a few hours post injection is a plus for Tc-99m label. Disadvantages of Tc-99m labelled leukocytes include genitourinary tract activity, which appears shortly after injection, and colonic activity, that appears by 4 hours post injection

Labelled leukocytes have been studied by many to be an accurate technique for the diagnosis of osteomyelitis in the setting of violated bones as well as in diabetic foot infection. The overall sensitivity and specificity of Tc-99m HMPAO labelled leukocytes is 88% and 91%, respectively, for osteomyelitis in previously violated bones. However, Tc99m HMPAO labelled leukocytes imaging is performed only after a positive finding on a three phase bone imaging, because the latter is highly sensitive but significantly less expensive, making it more appropriate as a first-line screening procedure. (Devillers et al., 2000) reported an overall sensitivity, specificity, and accuracy of 93%, 100%, and 96%, respectively, for Tc-99m HMPAO labelled leukocytes and 100%, 17%, and 53.3%, respectively, for Tc-99m MDP bone imaging. In our own experience combined Tc-99m HMPAO/Tc-99m MDP imaging proved useful in diagnosing osteomyelitis. The specificity of Tc-99m MDP bone scanning improved from 30% to 78% with the addition of Tc-99m

may be necessary due to prolonged circulation of labelled cells.

thereby obscuring potential foci of infections at these sites.

HMPAO labelled leukocytes (Figure 6).

**4.4 Radiolabelled leukocytes: Clinical utilities and applications** 

distribution is in question.

Labelled leukocytes imaging have been used in the diagnosis of orthopaedic implant infection after positive findings on three phase bone scanning. False positive scans can occur due to dystrophic ossification, peri-prosthetic granulomas, altered distribution of red marrow, and damage to the polyethelene surface of the prosthesis and metallosis. Combined leukocyte-marrow imaging can overcome many of the problems created by variable marrow distribution post-operatively. (Palestro et al., 1990) reported good results with combined In-111 labelled leukocytes/bone marrow imaging, with 86–100% sensitivity and 97–100% specificity in hip and knee prosthesis infections. (Joseph et al., 2001) also noted the ability of added sulphur colloid scanning to eliminate the false positive results. Our own experience suggest Tc-99m HMPAO labelled leukocytes scan appears significantly valuable in detecting osteomyelitis in patients with prosthetic implants (Figure 7).

Labelled leukocyte imaging is the procedure of choice for the evaluation of patients with diabetic foot. Sensitivity and specificity of In-111 labelled leukocytes for diabetic foot osteomyelitis is between 72%-100% and between 67%-100%, respectively. Sensitivity of Tc-99m HMPAO labelled leukocytes has been reported to be 90% and 93% while the specificity has been observed to be 86% and 100% by various groups. Interestingly, the combination of Tc-99m HMPAO labelled leukocytes scan with Tc-99m three phase bone scan has yielded both high sensitivity and high specificity (92.6% and 97.6%, respectively), moreover this combination is of benefit in patients with Charcot osteoarthropathy. The reported sensitivity

Radionuclide Infection Imaging: Conventional to Hybrid 85

the adjacent inflammatory site which may mask the abnormality or cause the appearance of a cold defect). MRI is presumably the modality of choice when evaluating patients for

In-111 labelled leukocytes scans are superior to Ga-67 for evaluation of suspected abscess in abdomen and pelvis due to the lack of a normal bowel excretory pathway. Some abscesses accumulate In-111 labelled leukocytes very slowly, and 48 hour delayed imaging may be necessary to identify these lesions. In appendicitis a focal area of increased activity in the right lower quadrant may be identified. Labelled leukocyte can be used to assess for disease activity and distribution of inflammatory bowel disease and excellent correlation is found between endoscopy, histology, and scintigraphic findings for disease extent and activity. (Annovazzi et al., 2005) reported in a meta-analysis that leukocytes labelled with In-111 oxine or Tc-99m HMPAO should be considered as the procedures of choice in acute phases

Labelled leukocyte imaging has been successfully utilized to detect both cardiovascular and central nervous system infections with limited clinical consequences. Leukocyte scintigraphy provides valuable information about contrast-enhancing brain lesions seen on radiological imaging. Positive findings indicate that the origin of the brain lesion is almost assuredly infectious; a negative result rules out infection with a high degree of certainty. However, false positive results can be seen in brain tumours, and false-negative results in patients receiving high-dose steroids. Labelled leukocyte imaging is the radionuclide procedure of choice for diagnosis of graft infection, with a sensitivity of more than 90%; neither duration of symptoms nor pre-treatment with antibiotics adversely affects the study. The specificity of labelled leukocyte imaging is more variable, ranging from 53% to 100%. Causes of false-positive results include peri-graft hematomas, bleeding, graft thrombosis, pseudoaneurysms, and graft endothelialisation, which occur within the first 1–2 weeks after

SPECT/CT has incremental value for interpretation of labelled leukocytes imaging for an array of clinical indications in different regions of the body, by distinguishing normal physiologic distribution from accumulation due to underlying infectious process. Benefit has been observed when characterizing foci of labelled leukocytes accumulation near the major vessels. The hybrid technology helps in discriminating blood-pool activity from infectious sites, particularly in evaluation of suspected vascular graft infection and fever of unknown origin. Moreover, SPECT/CT with Tc-99m HMPAO labelled leukocytes is useful to image bone and joint infections, providing accurate localization especially some cases where planar images alone are not able to distinguish soft tissue from bone and to precisely define the extent of infection, thus modifying clinical patient management and therapeutic approaches in several cases. In particular those with diabetic foot infection, it helps support treatment planning and avoiding more invasive procedures. (Filippi & Schillaci, 2006) more recently reported that SPECT/CT avoided unnecessary bone amputation in significant

(Filippi & Schillaci, 2006) have evaluated the usefulness of SPECT/CT for interpreting Tc-99m HMPAO labelled leukocytes in bone and joint infection. SPECT/CT fusion correctly characterized and localized the site of abnormal uptakes in all patients with osteomyelitis, having a substantial impact on the clinical management. Moreover, those patients with a suspicion of infection post orthopaedic implants, SPECT/CT offered a more accurate

of disease, since endoscopic and barium studies are contraindicated.

**4.5 Radiolabelled leukocytes: Hybrid SPECT/CT imaging** 

suspected vertebral osteomyelitis.

placement.

numbers of patients.

Fig. 7. A 70-year old female with history of left total knee replacement three years ago, presented with pain and swelling in the left knee prosthesis. Tc99m MDP bone scan show increased pool activity and intense increase tracer accumulation around left knee prosthesis. Tc-99m HMPAO labelled leukocytes scan showed increase tracer localization with rinds of tracer uptake at the femoral component of left knee prosthesis suggesting prosthetic infection.

of 92.6% and a specificity of 97.6% by (Poirier et al., 2002) for Tc-99m HMPAO/Tc-99m MDP bone imaging for the diagnosis of osteomyelitis in diabetic foot ulcers appear promising and it is believed that neuroarthropathy does not affect the performance of this scan. In our own institutional experience this combination for diabetic foot ulcers proved to be useful in diagnosing underlying osteomyelitis (Figure 8).

Fig. 8. A 50-year old male with history of diabetic right big toe amputation done 3 years ago, now presented with discharge from the right foot. Tc-99m HMPAO labelled leukocytes scan showed features consistent with osteomyelitis at right 3rd metatarsal bone with overlying soft tissue infection in the right distal foot.

Leukocyte labelled imaging is not as sensitive for infection of the spine as it is for other musculoskeletal infections and may be falsely negative in up to 80% of cases. The difficulty in interpretation may be related to the large percentage of spinal osteomyelitis which produces a cold, rather than a hot lesion (marrow uptake in the spine may be higher than in

Fig. 7. A 70-year old female with history of left total knee replacement three years ago, presented with pain and swelling in the left knee prosthesis. Tc99m MDP bone scan show increased pool activity and intense increase tracer accumulation around left knee prosthesis. Tc-99m HMPAO labelled leukocytes scan showed increase tracer localization with rinds of tracer uptake at the femoral component of left knee prosthesis suggesting prosthetic

of 92.6% and a specificity of 97.6% by (Poirier et al., 2002) for Tc-99m HMPAO/Tc-99m MDP bone imaging for the diagnosis of osteomyelitis in diabetic foot ulcers appear promising and it is believed that neuroarthropathy does not affect the performance of this scan. In our own institutional experience this combination for diabetic foot ulcers proved to be useful in

Fig. 8. A 50-year old male with history of diabetic right big toe amputation done 3 years ago, now presented with discharge from the right foot. Tc-99m HMPAO labelled leukocytes scan showed features consistent with osteomyelitis at right 3rd metatarsal bone with overlying

Leukocyte labelled imaging is not as sensitive for infection of the spine as it is for other musculoskeletal infections and may be falsely negative in up to 80% of cases. The difficulty in interpretation may be related to the large percentage of spinal osteomyelitis which produces a cold, rather than a hot lesion (marrow uptake in the spine may be higher than in

infection.

diagnosing underlying osteomyelitis (Figure 8).

soft tissue infection in the right distal foot.

the adjacent inflammatory site which may mask the abnormality or cause the appearance of a cold defect). MRI is presumably the modality of choice when evaluating patients for suspected vertebral osteomyelitis.

In-111 labelled leukocytes scans are superior to Ga-67 for evaluation of suspected abscess in abdomen and pelvis due to the lack of a normal bowel excretory pathway. Some abscesses accumulate In-111 labelled leukocytes very slowly, and 48 hour delayed imaging may be necessary to identify these lesions. In appendicitis a focal area of increased activity in the right lower quadrant may be identified. Labelled leukocyte can be used to assess for disease activity and distribution of inflammatory bowel disease and excellent correlation is found between endoscopy, histology, and scintigraphic findings for disease extent and activity. (Annovazzi et al., 2005) reported in a meta-analysis that leukocytes labelled with In-111 oxine or Tc-99m HMPAO should be considered as the procedures of choice in acute phases of disease, since endoscopic and barium studies are contraindicated.

Labelled leukocyte imaging has been successfully utilized to detect both cardiovascular and central nervous system infections with limited clinical consequences. Leukocyte scintigraphy provides valuable information about contrast-enhancing brain lesions seen on radiological imaging. Positive findings indicate that the origin of the brain lesion is almost assuredly infectious; a negative result rules out infection with a high degree of certainty. However, false positive results can be seen in brain tumours, and false-negative results in patients receiving high-dose steroids. Labelled leukocyte imaging is the radionuclide procedure of choice for diagnosis of graft infection, with a sensitivity of more than 90%; neither duration of symptoms nor pre-treatment with antibiotics adversely affects the study. The specificity of labelled leukocyte imaging is more variable, ranging from 53% to 100%. Causes of false-positive results include peri-graft hematomas, bleeding, graft thrombosis, pseudoaneurysms, and graft endothelialisation, which occur within the first 1–2 weeks after placement.

#### **4.5 Radiolabelled leukocytes: Hybrid SPECT/CT imaging**

SPECT/CT has incremental value for interpretation of labelled leukocytes imaging for an array of clinical indications in different regions of the body, by distinguishing normal physiologic distribution from accumulation due to underlying infectious process. Benefit has been observed when characterizing foci of labelled leukocytes accumulation near the major vessels. The hybrid technology helps in discriminating blood-pool activity from infectious sites, particularly in evaluation of suspected vascular graft infection and fever of unknown origin. Moreover, SPECT/CT with Tc-99m HMPAO labelled leukocytes is useful to image bone and joint infections, providing accurate localization especially some cases where planar images alone are not able to distinguish soft tissue from bone and to precisely define the extent of infection, thus modifying clinical patient management and therapeutic approaches in several cases. In particular those with diabetic foot infection, it helps support treatment planning and avoiding more invasive procedures. (Filippi & Schillaci, 2006) more recently reported that SPECT/CT avoided unnecessary bone amputation in significant numbers of patients.

(Filippi & Schillaci, 2006) have evaluated the usefulness of SPECT/CT for interpreting Tc-99m HMPAO labelled leukocytes in bone and joint infection. SPECT/CT fusion correctly characterized and localized the site of abnormal uptakes in all patients with osteomyelitis, having a substantial impact on the clinical management. Moreover, those patients with a suspicion of infection post orthopaedic implants, SPECT/CT offered a more accurate

Radionuclide Infection Imaging: Conventional to Hybrid 87

Tc-99m fanolesomab has been used for diagnosis of acute appendicitis. It has a good overall accuracy with a positive predictive value (PPV) of 74-87% and a negative predictive value (NPV) between 95-100%. A high NPV is helpful for the patients to avoid unnecessary surgery, however, a number of false positives have been an issue with this

Fig. 9. A 10-year old girl, presented with tenderness and swelling at right distal femur. Tc-99m MDP bone scan show hyperperfusion and increases tracer accumulation at the distal 1/3rd of right femur. Tc-99m Sulesomab imaging show increased tracer uptake at distal right

(Horger et al., 2003) showed that SPECT/CT changed the interpretation of radioimmunoscintigraphy with Tc-99m labelled anti-granulocyte antibodies in 28% of suggestive foci evaluated in 27 patients in whom relapsing post-traumatic osteomyelitis was

femur corresponding to the site seen on bone scan, confirming osteomyelitis.

**5.4 Tc-99m labelled Anti-granulocyte antibody: Hybrid SPECT/CT imaging** 

radiopharmaceutical.

anatomic localization of the site of infection than SPECT alone allowing differentiation between prosthesis and soft-tissue uptake. Similarly, (Bar-Shalom et al., 2006) observed that using In-111 labelled leukocyte SPECT/CT contributed to accurate identification of infection in 55% of patients suspected to have osteomyelitis and 67% of those suspected to have a vascular graft infection.
