WBC imaging

Agents: In-111 Oxine Tc-99m Ceretec (HMPAO)

Inflammtion

Acute

chronic

Leukocytes Ave Adult ~7000 WBC/microliter

Monocytes (5%)

Lymphocytes (30%)

Granulocytes (65%)

neutrophils

eosinophils

basophils

Labeling Procedure

1. Take 43mL(at least) blood with 7 mL ACD or 400U heparin plus 6mL 6% hetastarch

2. Sediment 50-60 minutes

3. transfer plasma, centrifuge @450g for 5min

4. Remove PPP and centrifuge @ 1000g for 5 min

5. Resuspend WBC button with 2mL 0.9% saline, add 9.1 mL sterile water, swirl for 20 seconds, add 2 mL 5% saline, followed by 10mL 0.9% saline, centrifuge @ 450g and discard liquid

Lyse RBC

6. Suspend in 2 mL 0.9% saline and add 0.5 mCi In-111 Oxine

7. Add 10mL PPP, centrifuge @450g for 5 min

8. Remove supernatant and suspend in 5 mL PPP

9. Inject 500 uCi In-111 oxine

WBC separatory technique

Gravity sedimentation

clinical considerations

sites of occult infection are difficult to diagnose

early diagnosis can cure most infections

delayed diagnosis is associated with increased mortality

CT and ultrasound are often used initially but cannot differentiate between infection and noninfectious process

Nuclear medicine allows for whole body imaging

important when no localizing signs are present

Hespan (HES)

synthetic polysaccharide colloid used as volume expander

sometimes* added to blood sample to increase erythrocyte edimentation rate and greater leukocyte recovery

cleared from body after administration

rarely allergic reactions reported

Anticoagulants

ACD - Anticoagulant citrate dextrose or Acid citrate dextrose

less adhesion to centrifuge tubes/syringes used in labeling procedures

no affinity for technetium

shown to be cytotoxic to cells (insignificant)

High cost when compared to heparin

heparin

1000-2000U Most commonly used

Low cost

some affinity for technetium

Tc-99m HMPAO vs. In-111 Oxine

In-111 oxine advantages

preferred for chronic processes(fever of unknown origin, infected prosthesis)

greater stability within granulocytes and inflammatory site

7h half life in blood compared to 4h BHL with Tc-99m HMPAO

high target to background ratio

used frequently for abdominal imaging

Tc-99m HMPAO Advantages

technetium availability

high count rate - enhanced image resolution

reduced radiation burden

selective granulocyte labeling

rapid diagnosis

often used for inflammatory processes in extreminities

In-111 oxine

Imaging Protocol

optimal imaging 24h post injection

prominent abscess to bacckground ratio

4-6 h for preliminary images

highest diagnostic specificity at 24 h

In-111 Oxine General Properties

67 Hour half life

Photopeaks at 171 and 245 keV

Lipid soluble

normal dose = 0.5 mCi

Penetrates neutrophil membranes where transchelation of In-111 to transferrin occurs

plasma half life = 7h

Tc-99m HMPAO

Tc-99m Ceretec General Properties

6 hour half life

Normal adult dose of 10-20 mCi

140 keV photopeak

highly lipophilic

diffuses into leukocyte and is converted to nondiffusible hydrophilic complex

plasma half life = 4h

Imaging Protocol

infection/inflammation detection within 4h and as early as 30 min after injection

bowel excretion seen at 4h

abdomen imaging normally performed at 30min and 3h

questionable diagnostic accurarcy due to nonspecific bowel accumulation

Blood sample precautions

consider all blood to be infectious

wear latex gloves/lab coats are all times

label all supplies with patient name and ID number

do not use needle smaller than 21 gauge

small diameter needles may damage cells