WBC imaging

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Blood sample precautions

do not use needle smaller than 21 gauge

small diameter needles may damage cells

label all supplies with patient name and ID number

wear latex gloves/lab coats are all times

consider all blood to be infectious

Tc-99m HMPAO

questionable diagnostic accurarcy due to nonspecific bowel accumulation

abdomen imaging normally performed at 30min and 3h

bowel excretion seen at 4h

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

Tc-99m Ceretec General Properties

plasma half life = 4h

diffuses into leukocyte and is converted to nondiffusible hydrophilic complex

highly lipophilic

140 keV photopeak

Normal adult dose of 10-20 mCi

6 hour half life

In-111 oxine

In-111 Oxine General Properties

plasma half life = 7h

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

normal dose = 0.5 mCi

Lipid soluble

Photopeaks at 171 and 245 keV

67 Hour half life

Imaging Protocol

highest diagnostic specificity at 24 h

4-6 h for preliminary images

prominent abscess to bacckground ratio

optimal imaging 24h post injection

Tc-99m HMPAO vs. In-111 Oxine

Tc-99m HMPAO Advantages

often used for inflammatory processes in extreminities

rapid diagnosis

selective granulocyte labeling

reduced radiation burden

high count rate - enhanced image resolution

technetium availability

In-111 oxine advantages

used frequently for abdominal imaging

high target to background ratio

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

greater stability within granulocytes and inflammatory site

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

WBC imaging

Anticoagulants

heparin

1000-2000U Most commonly used

Low cost

some affinity for technetium

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

Hespan (HES)

rarely allergic reactions reported

cleared from body after administration

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

synthetic polysaccharide colloid used as volume expander

clinical considerations

Nuclear medicine allows for whole body imaging

important when no localizing signs are present

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

delayed diagnosis is associated with increased mortality

early diagnosis can cure most infections

sites of occult infection are difficult to diagnose

WBC separatory technique

Gravity sedimentation

"buffy coat"

contains high leukocyte concentration

accumulation of cells of top of erythrocyte layer

at 1 hour, 70% of WBC's suspended in supernatant

minimize blood agitation

most popular separation method

Labeling Procedure

9. Inject 500 uCi In-111 oxine

8. Remove supernatant and suspend in 5 mL PPP

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

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

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

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

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

2. Sediment 50-60 minutes

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

Leukocytes Ave Adult ~7000 WBC/microliter

Granulocytes (65%)

basophils

eosinophils

neutrophils

Lymphocytes (30%)

Monocytes (5%)

Inflammtion

it is mainly the neutrophils and monocytes that are involved in the inflammatory response

chronic

Acute

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