Planning In Vivo Body Composition Studies in Humans - ACS

Chapter 3

Planning In Vivo Body Composition Studies in Humans

Downloaded by PENNSYLVANIA STATE UNIV on August 1, 2012 | http://pubs.acs.org Publication Date: December 26, 1991 | doi: 10.1021/bk-1991-0445.ch003

Kenneth J . Ellis Children's Nutrition Research Center, Department of Pediatrics, U.S. Department of Agriculture, Agricultural Research Service, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030

As multi-elemental analyses of body fluids and tissues become increasingly more sensitive, their interpretation may require additional knowledge about the relationship of the fluids and tissues to the composition of either the total body or specific organs. Until recently, only biopsy or autopsy data could be used to estimate total body composition in humans. Nuclear-based techniques, however, have been developed in a few centers for direct in vivo measurements of total body calcium, sodium, chlorine, nitrogen, phosphorus, potassium, hydrogen, carbon, and oxygen in man. Analyses of selected trace elements, cadmium, lead, and aluminum have also been developed for specific clinical or toxicological studies. Interest in the availability of these measurements, which often require specialized facilities, is increasing throughout the world. Activation and counting techniques routinely implemented for in vivo analyses in humans will be emphasized in this report. Techniques will be described that have levels of accuracy and precision of at least ± 3 to 5%. Institutional requirements and preferred nuclear techniques will be presented to assist those who are considering in vivo body composition studies in humans. Also included is information on the planning of these studies. Neutron activation is a well-established analytical technique for the in vitro analysis of biological samples. For in vivo analyses, however, neutron activation is limited by the radiation dose and exposure time, as well as by the irregular geometry of the body and its elemental composition. The long exposure times required for effective activation of many This chapter not subject to U.S. copyright Published 1991 American Chemical Society In Biological Trace Element Research; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


26

BIOLOGICAL TRACE ELEMENT RESEARCH

elements i n the body s i g n i f i c a n t l y reduce the range o f elements a v a i l a b l e f o r i n v i v o a n a l y s i s . Bulk elements (Ca, P, H, N) and s e l e c t e d t r a c e elements (Cd, Hg, Fe, Mn, I ) , i . e . , those w i t h l a r g e t h e r m a l n e u t r o n c r o s s - s e c t i o n s , have been examined i n v i v o ( 1 - 4 ) . N e v e r t h e l e s s , the elements that have been measured i n v i v o have p r o v i d e d u s e f u l c l i n i c a l , t o x i c o l o g i c a l , and b a s i c p h y s i o l o g i c a l i n f o r m a t i o n which o t h e r w i s e would not be o b t a i n a b l e i n t h e l i v i n g human ( 1 - 4 ) . A number o f i n v i v o t e c h n i q u e s have been i n v e s t i g a t e d , i n c l u d i n g n e u t r o n a c t i v a t i o n ( d e l a y e d and prompt p r o c e d u r e s ) , n u c l e a r resonant s c a t t e r i n g o f gamma-rays, i n e l a s t i c s c a t t e r i n g , p h o t o n u c l e a r p r o d u c t i o n , and the c o l l e c t i o n o f e x h a l e d r a d i o a c t i v e gases i n the b r e a t h a f t e r exposure to n e u t r o n s . A l t h o u g h the l a t t e r f o u r t e c h n i q u e s a r e o f c o n s i d e r a b l e i n t e r e s t , they w i l l not be addressed i n any d e t a i l i n t h i s paper, because e x p e r i e n c e w i t h t h e i r use on humans i s not s u f f i c i e n t t o e n a b l e an adequate assessment o f r.heir p o t e n t i a l . S e v e r a l review a r t i c l e s have been p u b l i s h e d on i n v i v o n e u t r o n a c t i v a t i o n a n a l y s i s t e c h n i q u e s ( 1 4 ) . The focus of t h i s paper w i l l be the t e c h n i q u e s ' r o u t i n e l y ' implemented f o r i n v i v o a n a l y s e s i n humans, and where p o s s i b l e , w i l l suggest which method i s p r e f e r r e d . I n each a p p l i c a t i o n , the magnitude of t h e r a d i a t i o n dosage has to be balanced a g a i n s t the m e d i c a l v a l u e o f the i n v i v o a n a l y s i s d a t a . My primary aim i s t o a s s i s t those who a r e c o n s i d e r i n g i j i v i v o body c o m p o s i t i o n s t u d i e s i n humans and t o p r o v i d e i n f o r m a t i o n h e l p f u l t o the p l a n n i n g o f these s t u d i e s . IN VIVO NEUTRON ACTIVATION ANALYSIS (IVNAA) Neutron R e a c t i o n s i n the Body. The b a s i c p r i n c i p l e o f in v i v o e l e m e n t a l a n a l y s i s i s t h e d e t e c t i o n o f gamma-rays e x t e r n a l l y e m i t t e d from the body which a r e p r e s e n t d u r i n g o r a f t e r exposure t o n e u t r o n s . A l t h o u g h the p r i n c i p l e i s q u i t e s i m p l e , the p h y s i c a l and e x p e r i m e n t a l f a c t o r s which determine whether or n o t an element can be measured a c c u r a t e l y and w i t h p r e c i s i o n a r e f r e q u e n t l y complex. A number o f p h y s i c a l f a c t o r s such as n e u t r o n r e a c t i o n c r o s s - s e c t i o n , c o m p l e x i t y o f the gamma r a y s p e c t r a , i n t e r f e r e n c e peaks, amount o f element i n the body, n e u t r o n f l u x , and exposure and c o u n t i n g times governs the interactions. The g e n e r a l c o m p o s i t i o n and geometry o f the human body a r e beyond the i n v e s t i g a t o r ' s c o n t r o l ; the o n l y v a r i a b l e s which the e x p e r i m e n t e r may d e t e r m i n e a r e the n e u t r o n s o u r c e , i r r a d i a t i o n geometry, and c o u n t i n g t e c h n i q u e . Thermal n e u t r o n r e a c t i o n s a r e used most commonly f o r i n v i v o a n a l y s e s . These n e u t r o n s a r e produced m a i n l y i n t h e body by s c a t t e r i n g f a s t n e u t r o n s on body hydrogen. The c h a r a c t e r i s t i c s o f the n e u t r o n r e a c t i o n s c o n s i d e r e d f o r IVNAA are l i s t e d i n T a b l e I f o r the elements n o r m a l l y measured i n v i v o . The v a l u e s i n the l a s t column g i v e o n l y a sense o f the r e l a t i v e s e n s i t i v i t y f o r each element; the c o m p l e x i t y o f the gamma s p e c t r a , background l e v e l s , o r p o s s i b l e i n t e r f e r e n c e gamma-rays a r e not c o n s i d e r e d .

In Biological Trace Element Research; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


Calcium Potassium Sodium Chlorine Cadmium Oxygen Phosphorus

48 Ca 40! 23 Na 37 CI 113 Cd 16 3li

Target Isotope

, P

Y

Y

fl

31p " 28^ P(n,a) A l

77

Y

N(n, ) ^ ^N(n,2n)^N *°Ca(n, ) Ca t^tural activity Na(n, )o Na u

Neutron Reaction

2.223 10.83 0.511 3.084 1.461 2.754 2.168 0.559 6.134 1.779

Gamma Energy (MeV)

1.00 0.15 2.00 0.92 0.11 1.00 0.42 0.40 0.69 1.00

Emission Rate

Q

Prompt Prompt 9.96 min 8.72 m i n 1.277x10 g 15.02 h 37.3 min Prompt 7.2 s e c 2.24 min

HalfLife

1550 0.44 0.61 0.022 c 0l5 0.10 0.55 7.20 1.57

Relative Detection . Sensitivity

Main R e a c t i o n s C o n s i d e r e d f o r I n V i v o Neutron A c t i v a t i o n A n a l y s i s

*ICRP 23 - R e f e r e n c e Man L i v e r cadmium (3 ug/g) and k i d n e y cadmium (3.0 mg) a r e assumed to r e p r e s e n t 50-75% of t o t a l body content. Jj< 20 cpm per g K C o m p l e x i t y o f s p e c t r a , background l e v e l s , and i n t e r f e r e n c e peaks are not c o n s i d e r e d .

0.024 43000 780

c

1000 140 100

Hydrogen Nitrogen

h

7000 1800

Element

95

Amount in Body (g)

Table I .



28


S e l e c t i o n o f Neutron Source. The t h r e e types o f n e u t r o n s o u r c e s c u r r e n t l y used f o r i n v i v o a c t i v a j ^ g n i n m a n u r e l i s t e d i n Tgjjje I I . The r a d i o a c t i v e s o u r c e s a r e Pu/Be, Am/Be, and C f . The Pu and Am s o u r c e s have the advantage o f l o n g h a l f - l i v e s (87.5 y r and 458 y r , r e s p e c t i v e l y ) , thus p r o v i d i n g a r e l a t i v e l y c o n s t a n t n e u t r o n output w i t h time. Cf has a much s h o r t e r h a l f - l i f e (2.65 y r ) , and r e q u i r e s replacement a t r e g u l a r i n t e r v a l s , which adds t o the t o t a l c o s t o f the system. The n e u t r o n g e n e r a t o r has the unique advantage o f no n e u t r o n beam ( t h u s no major h e a l t h p h y s i c s c o n s i d e r a t i o n s ) except when the u n i t i s o p e r a t i n g . I t does d e l i v e r h i g h e r energy n e u t r o n s , so t h a t the dose p e r n e u t r o n i s i n c r e a s e d . These systems u s u a l l y r e q u i r e more maintenance than do r a d i o a c t i v e s o u r c e s , t h e i r output d e c r e a s e s w i t h use, and tube replacement r e q u i r e s t h a t t h e system be c o m p l e t e l y r e c a l i b r a t e d . The ranges o f t o t a l s o u r c e o u t p u t , f l u x (n/cm x sec) i n c i d e n t on the body, and i r r a d i a t i o n and c o u n t i n g times a r e a l s o g i v e n i n T a b l e I I . The predominant r e a c t i o n s f o r c l i n i c a l a p p l i c a t i o n s have been the t h e r m a l (n,y) r e a c t i o n s l i s t e d i n T a b l e I . I f one i s not p l a n n i n g l o n g - t e r m s t u d i e s t h a t i n c l u d e i n v i v o measurements o r e x a m i n a t i o n o f o n l y a s p e c i f i c organ o r element, Cf should be t h e f i r s t s o u r c e t o c o n s i d e r f o r t h i s l i m i t e d a p p l i c a t i o n . A c t i v a t i o n and C o u n t i n g G e o m e t r i e s . The most b a s i c requirement i s t h a t the whole body i r r a d i a t i o n and d e t e c t o r g e o m e t r i e s subtend a s o l i d a n g l e that i s as g r e a t as p o s s i b l e . C l a s s i c examples o f t h i s approach a r e the 2n i r r a d i a t i o n chamber and whole-body c o u n t e r j ^ B a y l o r C o l l e g e o f M e d i c i n e ( 5 ) . The i r r a d i a t o r uses 56 Am/Be s o u r c e s (15.5 C i each) d i s t r i b u t e d above and below the s u b j e c t . The whole body c o u n t e r comprises 32 N a l d e t e c t o r s ( c r y s t a l s i z e o f 10 cm x 10 cm x 46 cm each) a r r a n g e d i n two banks above and below the s u b j e c t . The c o u n t i n g response i s r e l a t i v e l y i n v a r i a n t to the d i s t r i b u t i o n of a c t i v i t y w i t h i n t h e body, thus e n a b l i n g a b s o l u t e measurements. Each d e t e c t o r can be o p e r a t e d as a s i n g l e u n i t o r i n c o m b i n a t i o n s t o o p t i m i z e the t o t a l s i g n a l t o background r a t i o . T h i s system e n a b l e s K c o u n t i n g i n i n f a n t s through a d u l t s ( E l l i s , K.J. and S h y p a i l o , R.J., Phys. Med. B i o l . , i n p r e s s ) . A more t y p i c a l whole body c o u n t e r arrangement i s t h a t a t the Leeds G e n e r a l I n f i r m a r y ( 6 ) . T h i s c o u n t e r has 8 N a l d e t e c t o r s ( c i r c u l a r c r y s t a l s o f 15 cm d i a m e t e r x 10 cm t h i c k n e s s ) , 4 above and 4 below the s u b j e c t . Another approach, s e l e c t e d m a i n l y f o r e c o n o m i c a l r e a s o n s , i s the 'shadow s h i e l d ' c o u n t e r which u s u a l l y comprises two l a r g e Nal c r y s t a l s , t y p i c a l l y 30 cm d i a m e t e r by 10 cm t h i c k n e s s , t h a t a r e s h i e l d e d by a l e a d c o v e r i n g . I n t h i s c a s e , the s u b j e c t must be scanned between the d e t e c t o r s a t a r a t e determined by the h a l f - l i f e o f the r a d i o i s o t o p e and t h e d e s i r e d l e v e l o f p r e c i s i o n . Background and D e t e c t o r S h i e l d i n g . A s h i e l d e d whole body c o u n t e r i s needed t o d e t e c t low l e v e l s o f induced a c t i v i t y . I t s h o u l d be l o c a t e d r e a s o n a b l y c l o s e t o t h e i r r a d i a t i o n chamber, but a t a s u f f i c i e n t d i s t a n c e t o a v o i d a c t i v a t i n g t h e c r y s t a l s ( ^ i n c r e a s i n g t h e background s i g n a l . The B a y l o r 1000 C i Am/Be i r r a d i a t o r i s w i t h i n 100 f t o f the low background


3. ELLIS

29



T a b l e I I . Three Types o f Neutron Sources C u r r e n t l y i n Use f o r I n V i v o Neutron A c t i v a t i o n A n a l y s i s o f Man.

Type o f Source Characteristics T o t a l source output ( n / s e c )

238 -.-Pu/Be Am/Be

?t

.

Neutron Generator

?

Cf

7

2.0xl0 -l.lxl0

9

9 10 2.2x10 -1.8x10 u

10 Up to 3x10

Incident neutron flux density i n body (n/cm - s e c )

Ixl0 -5xl0

Irradiation

2-30 min

10-30 min

2-40 min

10-40 min

Delayed Gamma Spectra

Hand, t o r s o , v h o l e body Ca, P, C I , Na

Hand, forearm, s p i n e Ca

T o t a l body N, Ca, Na, CI, P

Prompt Gamma Spectra

L i v e r and k i d n e y Cd T o t a l and p a r t i a l body N

L i v e r and k i d n e y Cd T o t a l and p a r t i a l N, Ca

T o t a l Body C (pulsed)

Advantages

R e l i a b l e , constant output, long half-life, p o r t a b l e , moderate cost

R e l i a b l e , constant output, portable very s m a l l source H i g h e s t thermal f l u x per u n i t dose

Beam on o n l y vhrn r e q u i r e d . Good energy f o r t h i c k s e c t i o n s . No dosr when not i n use.

Disadvantages

Continuously acti v e , some r e g u l a tory d i f f i c u l t i e s i n d i s p o s a l of s o u r c e may be encountered.

Continuously a c t i v e short h a l f - l i f e replacement, d i s posal, calibration at 5-yr i n t e r v a l s

More maintenance r e q u i r e d than f o r radionuclide s o u r c e s . Cost of replacement tubes adds t o expense. High dose per u n i t neutron

time

C o u n t i n g time

3

4

5

3xl0 -10

6

3

3xl0 -5xl0

5

10 sec-5 min

Applications


30



whole body c o u n t e r . The s h i e l d i n g r e q u i r e d f o r prompt gamma s t u d i e s , a l t h o u g h s m a l l e r i n p h y s i c a l s i z e because o f the lower s o u r c e a c t i v i t y , i s more complex because the d e t e c t o r s must m o n i t o r t h e s i g n a l e m i t t e d from the body s i m u l t a n e o u s l y w i t h the n e u t r o n i r r a d i a t i o n . One o b v i o u s c o n s t r a i n t i s that the d e t e c t o r s a r e n o t p l a c e d i n f u l l view o f the neutron beam. N e v e r t h e l e s s , i t i s e s t i m a t e d that 1-5% o f the neutron f l u x i s s c a t t e r e d towards the d e t e c t o r s from the s u b j e c t ' s body. The number o f n e u t r o n s r e a c h i n g the d e t e c t o r s i s reduced by s u r r o u n d i n g t h e d e t e c t o r s w i t h p o l y e t h y l e n e o r wax impregnated w i t h l i t h i u m o r boron.

N a l and Ge D e t e c t o r Systems. The major c o n s i d e r a t i o n g o v e r n i n g the c h o i c e o f d e t e c t o r s i s that c o u n t i n g e f f i c i e n c y be maximized w h i l e an a c c e p t a b l e energy r e s o l u t i o n i s m a i n t a i n e d a t a r e a s o n a b l e c o s t . N o r m a l l y , the f i r s t c h o i c e i s N a l because of i t s h i g h e r d e t e c t i o n e f f i c i e n c y a t the lower c o s t . I f the spectrum i s complex, the h i g h e r energy r e s o l u t i o n o f Ge d e t e c t o r s may be needed. T h i s improvement i n energy r e s o l u t i o n i s o b t a i n e d o n l y a t the expense o f d e t e c t i o n e f f i c i e n c y and a t a major i n c r e a s e i n the c o s t o f the system. The N a l c r y s t a l s t y p i c a l l y used f o r IVNAA have e f f i c i e n c i e s that a r e 10 t o 20 times g r e a t e r than the l a r g e r (>25% e f f i c i e n c y ) Ge d e t e c t o r s and a t o n e - t e n t h the c o s t . Whether s p e c i f i c o r g a n s , r e g i o n s of the body, o r t h e whole body i s t o be measured w i l l determine the p h y s i c a l arrangement o f the d e t e c t o r system. The geometry of t h e c o u n t e r and i t s d e t e c t i o n e f f i c i e n c y a r e i n t e r d e p e n d e n t , a g a i n governed m a i n l y by c o s t . M u l t i d e t e c t o r a r r a y s r e q u i r e computer-based o p e r a t i o n s f o r d a t a c o l l e c t i o n and a n a l y s e s . For t h e measurement o f induced a c t i v i t i e s o f c a l c i u m , sodium, c h l o r i n e , and phosphorus, N a l d e t e c t o r s , housed i n low-background rooms, a r e used. F o r the prompt gamma measurements o f body n i t r o g e n , hydrogen, and c a r b o n , n e u t r o n - s h i e l d e d l a r g e volume (15 cm d i a m e t e r x 15 cm t h i c k n e s s ) N a l c r y s t a l s have proven a c c e p t a b l e . Recent i n v e s t i g a t i o n s by Ryde e t a l . (7) have shown that body c a l c i u m can be d e t e c t e d i n v i v o by the prompt gamma t e c h n i q u e , i f Ge d e t e c t o r s a r e used.

D o s i m e t r y . Any neutron exposure, no matter how s m a l l , can be a s s i g n e d some l e v e l o f r i s k . T h e r e f o r e , i t i s e s s e n t i a l to weigh the b e n e f i t s o f such measurements a g a i n s t the r i s k s . The World H e a l t h O r g a n i z a t i o n (WHO) has examined the r i s k s a s s o c i a t e d w i t h d i f f e r e n t l e v e l s o f r a d i a t i o n and has proposed the t h r e e dosage c a t e g o r i e s l i s t e d i n T a b l e I I I ( 8 ) . The


3. ELLIS

Planning In Vivo Body Composition Studies in Humans Table I I I .

Dose (mSv) G u i d e l i n e s f o r I n V i v o Activation Analysis

WHO Category


I

Within variations of n a t u r a l background

Body R e g i o n s Exposed

Order o f magnitude of dose ( m S v ) Range o f whole body doses (mSv) Dose t o s i n g l e organ (mSv): Thyroid L i v e r or kidney Gonads a

III

II

W i t h i n dose limits for general public

With dose l i m i t s f o r persons occupationally exposed to radia t ion

0.1

1.0

10

< 0.5

0.5-5.0

5.0-50

< 17 < 8.3 < 2.0

17-170 8.3-83 2.0-20

170-1700 83-830 20-200

lmSv = 100 mrem

c a t e g o r i e s a r e h e l p f u l i n i d e n t i f y i n g the r e l a t i v e exposure l e v e l s used f o r body c o m p o s i t i o n measurements. The WHO r e p o r t i n d i c a t e s t h a t c a t e g o r y I dosages n e i t h e r r e q u i r e p a r t i c u l a r r a d i a t i o n p r o t e c t i o n nor pose r a d i o b i o l o g i c a l problems; i . e . , any r e s u l t a n t r i s k would be c o n s i d e r e d n e g l i g i b l e . Most o f the d e l a y e d IVNAA procedures a r e w i t h i n the range of c a t e g o r y I I . These WHO g u i d e l i n e s a r e observed i n the UK f o r i_n v i v o n e u t r o n a c t i v a t i o n techniques. Most i n v e s t i g a t i o n s use dosages that a r e w e l l w i t h i n the WHO c a t e g o r i e s I I and I I I . Whole-body c a l c i u m measurements, f o r example, can be made a t a p r e c i s i o n of ± 1 X w i t h dosages as low as 2.5 mSv (250 mrem). Whole body n i t r o g e n measurements a r e r o u t i n e l y performed a t dosages below 0.3 mSv (30 mrem). RESEARCH APPLICATIONS AND ESTABLISHED PROCEDURES Body C a l c i u m and Bone M i n e r a l Mass. T o t a l o r p a r t i a l body c a l c i u m has been the most w i d e l y s t u d i e d element. The m a j o r i t y of the s t u d i e s have r e p o r t e d on the v a r i o u s d i s e a s e c o n d i t i o n s i n which c a l c i u m i s l o s t ; the dominant i n v e s t i g a t i o n s a r e those of post-menopausal o s t e o p o r o s i s ( 2 ) . Body c a l c i u m l e v e l s have s e r v e d as an index o f the p r o g r e s s i v e n a t u r e o f d i s e a s e s that a f f e c t the s k e l e t o n and a l s o as a monitor o f the e f f i c a c y o f treatment. To q u a n t i f y the degree o f d e m i n e r a l i z a t i o n i n the p a t i e n t g r o u p s , r e f e r e n c e v a l u e s must be e s t a b l i s h e d on the


32



b a s i s o f age, body s i z e , r a c e , and s e x f o r the g e n e r a l p o p u l a t i o n . Bone c a l c i u m has been determined f o r the whole body, t h e t r u n k , t h e s p i n e , and the a p p e n d i c u l a r s k e l e t o n by n e u t r o n a c t i v a t i o n a n a l y s i s ( 1 - 4 ) . Bone m i n e r a l content can a l s o be e s t i m a t e d by computerized a x i a l tomography (CT s c a n n i n g ) a t a h i g h e r exposure dosage o r i n body r e g i o n s by photon a b s o r p t i o m e t r y ( 2 ) . I t i s important t o n o t e , however, t h a t when a v a i l a b l e , the measurement p r e f e r r e d i s t h a t o f t o t a l body c a l c i u m . I t has served as t h e ^ r e f e r e n c e s t a n d a r d ' f o r the c a l i b r a t i o n o f these two a l t e r n a t e t e c h n i q u e s . Body N i t r o g e n and P r o t e i n Mass. Measurement o f body n i t r o g e n by prompt gamma n e u t r o n a c t i v a t i o n i s c u r r e n t l y the most d i r e c t method by which t o determine body p r o t e i n mass. I n new i n s t a l l a t i o n s where n i t r o g e n i s the o n l y element t o be d e t e r m i n e d , t h e f a c i l i t y s h o u l d employ r a d i o a c t i v e n e u t r o n s o u r c e s . Such f a c i l i t i e s a r e r e l i a b l e , r e l a t i v e l y i n e x p e n s i v e , r e q u i r e minimum f l o o r space (< 3 m x 8 m), and can use commercial e l e c t r o n i c s and s o f t w a r e . I n a d d i t i o n , gammas from body sodium, c h l o r i n e , phosphorus, and c a l c i u m , a l t h o u g h weak, can be observed i n t h e prompt s p e c t r a . Body c a l c i u m i s a l r e a d y b e i n g measured s e q u e n t i a l l y u s i n g Ge d e t e c t o r s ( 7 ) . The h i g h e r dose, l o s s o f a b s o l u t e measurements, and reduced p r e c i s i o n must undergo a d d i t i o n a l improvements b e f o r e t h i s approach can be recommended f o r t h e measurement o f c a l c i u m . One can e x p e c t , however, t h a t development i n t h i s d i r e c t i o n w i l l be c o n t i n u e d . I f t h e c o s t o f Ge d e t e c t o r s can be reduced, the dosage m a i n t a i n e d a t t h e l e v e l c u r r e n t l y used f o r n i t r o g e n , and the p r e c i s i o n improved t o 3% o r b e t t e r , the prompt-gamma t e c h n i q u e c o u l d r e p l a c e t h e c o u n t i n g o f the d e l a y e d a c t i v i t y i n the body. I f one had t o choose o n l y one type o f system, prompt o r d e l a y e d gamma c o u n t i n g , t h e c h o i c e w i l l depend on t h e importance p l a c e d on t h e immediate need f o r m u l t i - e l e m e n t a l c a p a b i l i t y . Both c r o s s - s e c t i o n a l and l o n g i t u d i n a l s t u d i e s have p r o v i d e d e s t i m a t e s o f p r o t e i n mass and n i t r o g e n b a l a n c e i n f o r m a t i o n i n h e a l t h y and d i s e a s e d humans. C l i n i c a l i n v e s t i g a t i o n s have i n c l u d e d t h e e x a m i n a t i o n o f body n i t r o g e n a f t e r major s u r g e r y , changes i n p a t i e n t s r e c e i v i n g t o t a l p a r e n t e r a l n u t r i t i o n , d i e t a r y support f o r cancer p a t i e n t s , and the e f f e c t s o f p r o t e i n - s p a r i n g d i e t s f o r weight r e d u c t i o n i n o b e s i t y (9-13). Other Elements and A d d i t i o n a l I n V i v o Techniques. The i n v i v o prompt gamma measurements o f k i d n e y and l i v e r cadmium l e v e l s i n humans a r e c u r r e n t l y the o n l y d i r e c t methods f o r a c c u r a t e assessments o f c u m u l a t i v e exposure ( 1 4 ) . E x a m i n a t i o n o f i n d u s t r i a l l y - e x p o s e d p o p u l a t i o n s have l e d t o a r e d e f i n i t i o n o f the c r i t i c a l c o n c e n t r a t i o n o f cadmium f o r the k i d n e y , an e v a l u a t i o n o f t h e r e l a t i o n s h i p o f cadmium l e v e l i n t h e k i d n e y to l e v e l s i n b l o o d and u r i n e , and o f a i r m o n i t o r i n g d a t a (15-17). I n v i v o X-ray f l u o r e s c e n c e (IVXRF) t e c h n i q u e s have a l s o been d e v e l o p e d , m a i n l y when n e u t r o n a c t i v a t i o n i s not p r a c t i c a l ( l o w s e n s i t i v i t y o r h i g h d o s e ) . These t e c h n i q u e s a r e s i m i l a r t o those o f p a r t i a l body prompt n e u t r o n a c t i v a t i o n ; the i n t e r e s t e d r e a d e r i s r e f e r r e d t o s e v e r a l reviews (18-20). IVXRF


3. ELLIS



t e c h n i q u e s a r e used t o measure i o d i n e c o n t e n t and i t s d i s t r i b u t i o n i n the t h y r o i d ; l e a d and s t r o n t i u m i n t e e t h and bones; mercury i n the s k u l l and b r a i n ; and cadmium c o n c e n t r a t i o n i n the r e n a l c o r t e x (18,21). Measurements o f body sodium, c h l o r i n e , and phosphorus a r e a l s o r o u t i n e l y o b t a i n e d , but have not been u t i l i z e d to any major e x t e n t i n c l i n i c a l r e s e a r c h p r o t o c o l s . I n v i v o methods f o r measuring o t h e r e l e m e n t s , among them, c a r b o n , i r o n , aluminum, s e l e n i u m , copper and s i l i c o n , have been d e v e l o p e d . An assessment o f t h e i r c o n t r i b u t i o n to h e a l t h c a r e o r a recommendation t h a t they be c o n s i d e r e d i n the i n i t i a l p l a n n i n g o f i n v i v o e l e m e n t a l s t u d i e s would be premature (1-4,22,23). A b s o l u t e o r S e q u e n t i a l Measurements. One o f the s t r e n g t h s o f the IVNAA measurements has been t h e i r use i n l o n g term-balance s t u d i e s . P r e v i o u s r e p o r t s have shown t h a t the c l a s s i c a l b a l a n c e t e c h n i q u e s i n c o r r e c t l y e s t i m a t e the changes that o c c u r i n v i v o ( 2 4 ) . The time i n t e r v a l between two i n v i v o measurements w i l l d e t e r m i n e the s e n s i t i v i t y o f i n v i v o d a t a f o r b a l a n c e s t u d i e s ( T a b l e I V ) . I n p l a n n i n g an i n v i v o system, a b s o l u t e c a l i b r a t i o n

Table IV. S e n s i t i v i t y of In Vivo Balance i n an I n d i v i d u a l

Average B a l a n c e S e n s i t i v i t i e s

Time Interval between Measurements

2 1 3 6 i 3 5

Ca (± mg/d)

wk mo mo mo yr yr yr

-

110 57 18 11

Estimates of D a i l y Intake

Physiological Balance

Studies

(M) (F)

1000

-8.7 -9.5

N (± g/d)

K (+ mmol/d)

1.78 0.59 0.30 0.15 0.05 0.03

7.10 3.53 1.18 0.59 0.29 0.10 0.06

16

84.4

-0.019 -0.014

-0.035 -0.023

S i g n i f i c a n t change between two measurements a t the p < 0.01 ^evel E s t i m a t e d on the b a s i s o f t o t a l body change between ages 25 and 65, assuming a c o n s t a n t r a t e o f l o s s due to a g i n g .



34


may not be n e c e s s a r y i f o n l y s e q u e n t i a l measurements a r e to be made. The p r e c i s i o n f o r repeated s t u d i e s on the same i n d i v i d u a l i s u s u a l l y g r e a t e r than that f o r an a b s o l u t e c a l i b r a t i o n . The a b s o l u t e v a l u e i s needed, however, i f i t i s important to r e l a t e an observed i n c r e a s e i n the body to r e p l a c e a d e f i c i e n c y , o r an increment above an a l r e a d y normal l e v e l . Optimum use of the IVNAA t e c h n i q u e s w i l l be a c h i e v e d when a b s o l u t e measurements a r e made. T h e i r f u l l d i a g n o s t i c p o t e n t i a l can best be r e a l i z e d when a h e a l t h y r e f e r e n c e p o p u l a t i o n i s a l s o examined. Body c o m p o s i t i o n d a t a a r e more f u l l y u t i l i z e d when combined w i t h o t h e r c l i n i c a l o r b i o c h e m i c a l i n d i c e s f o r the a s s e s s i n g the h e a l t h o r d i s e a s e s t a t u s o f the i n d i v i d u a l . Nitrogen measurements, f o r example, a r e more u s e f u l when used i n c o n j u n c t i o n w i t h measurements o f body potassium and water. The c o m b i n a t i o n e n a b l e s a more comprehensive view o f the combined changes t h a t can o c c u r i n the l e a n t i s s u e mass o f d i f f e r e n t body compartments ( 2 5 ) . PLANNING OF IN VIVO STUDIES I n s t i t u t i o n a l I n f r a s t r u c t u r e . A more widespread i n t e r e s t i n n o n i n v a s i v e t e c h n i q u e s w i l l emerge as the c l i n i c a l community c o n t i n u e s to r e c o g n i z e t h e i r p o t e n t i a l to p r o v i d e unique i n f o r m a t i o n on human body c o m p o s i t i o n . I n v i v o n e u t r o n a c t i v a t i o n i s s u f f i c i e n t l y advanced to warrant c o n s i d e r a t i o n of the m e d i c a l economics i n p l a n n i n g the next phases o f development. A l t h o u g h each system b u i l t to date has been custom d e s i g n e d , the i n t e g r a t e d l a b o r a t o r y concept used a t the newest f a c i l i t i e s a t B a y l o r C o l l e g e o f M e d i c i n e i n Houston, Texas, s h o u l d h e l p reduce some c o s t s f o r o t h e r c e n t e r s ( 5 ) . I t seems best t o a v o i d the p r o l i f e r a t i o n o f lower c o s t equipments which w i l l c o n s i d e r a b l y compromise the a c c u r a c y and p r e c i s i o n of procedures t h a t can be o b t a i n e d w i t h l a r g e r s t a t e - o f - t h e - a r t systems. The f o l l o w i n g s u g g e s t i o n s , t h e r e f o r e , a r e aimed p r i m a r i l y a t i n s t i t u t i o n s p l a n n i n g to e s t a b l i s h f i x e d i n s t a l l a t i o n s w i t h a s t r o n g emphasis on m u l t i - e l e m e n t a l a n a l y s i s . F o r t h i s a p p l i c a t i o n , the i r r a d i a t i o n f a c i l i t y , i n c l u d i n g the n e u t r o n s o u r c e s , s h o u l d be l o c a t e d w i t h i n r e a s o n a b l e p r o x i m i t y ( - 3 0 m)to the c o u n t i n g equipment, a l t h o u g h a t a s u f f i c i e n t d j g j a n c e o r w i t h adequate s h i e l d i n g (2 m c o n c r e t e f o r 1000 C i Am/Be s o u r c e ) to p r o t e c t the d e t e c t o r s from n e u t r o n damage. The d a t a c o l l e c t i o n and p u l s e h e i g h t a n a l y s i s t e c h n i q u e s w i l l r e q u i r e a computer-based system. S e v e r a l c o n s i d e r a t i o n s emphasize the advantage of l o c a t i n g these f a c i l i t i e s a t major c l i n i c a l c e n t e r s where the best p o s s i b l e equipment, i n terms o f s e n s i t i v i t y , low dose, and t e c h n i c a l e x p e r t i s e , would be a v a i l a b l e . The requirements f o r c l i n i c a l and r e s e a r c h use would p r o b a b l y r e s u l t i n h i g h p r o d u c t i v i t y on a 24-h b a s i s . A l t h o u g h some p a t i e n t s would be i n c o n v e n i e n c e d by h a v i n g t o t r a v e l to a r e g i o n a l c e n t e r , i t i s l e s s e x p e n s i v e and more p r o d u c t i v e than to e s t a b l i s h s m a l l e r f a c i l i t i e s a t a number o f h o s p i t a l s . The r e g i o n a l approach a l s o has an advantage i n t h a t a v a r i e t y o f o t h e r s o p h i s t i c a t e d procedures and equipment a v a i l a b l e f o r d i a g n o s i s and therapy,



3.

ELLIS


f o r example, CT s c a n n i n g , n u c l e a r magnetic imaging, n u c l e a r m e d i c i n e , and u l t r a s o u n d imaging, c o u l d be used i n c o n j u n c t i o n w i t h the IVNAA a n a l y s e s . These procedures a r e g e n e r a l l y complementary r a t h e r than c o m p e t i t i v e . The p a t i e n t i s o f f e r e d the best p o s s i b l e s e r v i c e when a v a r i e t y of t e c h n i q u e s i s available. One i m p o r t a n t e x c e p t i o n to the r e g i o n a l approach i s the use of s m a l l e r prompt gamma systems to a s s e s s body p r o t e i n s t a t u s . S u c c e s s f u l systems have been e s t a b l i s h e d worldwide i n c l i n i c a l s e t t i n g s ( T o r o n t o , Canada; Brookhaven, New York; Houston, Texas; A u c k l a n d , New Z e a l a n d ; Swansea, Wales; E d i n b u r g h , S c o t l a n d ; and Menai, A u s t r a l i a ) (5,7,26-30). A d d i t i o n a l systems a r e b e i n g planned f o r New York, G a l v e s t o n , B o s t o n , and San F r a n c i s c o i n the US a l o n e ( E l l i s K J , B a y l o r C o l l e g e o f M e d i c i n e , p e r s o n a l communication, 1989). T h i s procedure can be expected to be d i s p e r s e d even i n t o g e n e r a l h o s p i t a l s once the equipment becomes r e l i a b l e ; i s shown to r e q u i r e minimum maintenance; and i s packaged i n t o a ' t u r n - k e y ' i n s t r u m e n t r e d u c i n g t e c h n i c a l support r e q u i r e m e n t s . L o c a t i o n , D e s i g n , and Accommodation Requirements. The IVNAA f a c i l i t y s h o u l d have easy a c c e s s f o r p a t i e n t s from the h o s p i t a l f l o o r s and f o r o u t p a t i e n t s . The accommodation s h o u l d be d e s i g n e d so t h a t o p e r a t i n g p e r s o n n e l a r e not exposed to e x c e s s i v e r a d i a t i o n . The heavy s h i e l d i n g of the i r r a d i a t i o n and c o u n t i n g equipment f o r the induced a c t i v i t y measurements w i l l r e q u i r e f l o o r space on ground l e v e l o r below. T h i s requirement i s recommended a l t h o u g h not n e c e s s a r y f o r the prompt gamma system. W a i t i n g a r e a s , changing rooms, and a c l i n i c a l e x a m i n a t i o n a r e a f o r p a t i e n t s s h o u l d be p a r t of the t o t a l f a c i l i t y . A l t h o u g h an e l e c t r o n i c s workshop i s recommended, adequate maintenance can u s u a l l y be p r o v i d e d by the c e n t r a l s e r v i c e s of the i n s t i t u t i o n . There a r e no s p e c i a l e l e c t r i c a l power r e q u i r e m e n t s . I f Ge d e t e c t o r s a r e used, a r e g u l a r s u p p l y of l i q u i d n i t r o g e n i s needed. R o u t i n e h o s p i t a l h e a l t h p h y s i c s s u p p o r t i s adequate once i n s t a l l a t i o n i s completed. S t a f f i n g f o r R o u t i n e Measurements. A p r o f e s s i o n a l l y q u a l i f i e d s c i e n t i s t o r c l i n i c i a n i s r e q u i r e d to s u p e r v i s e the work and ensure q u a l i t y c o n t r o l . The measurements can be performed by n u c l e a r m e d i c i n e t e c h n i c i a n s . T h e i r t r a i n i n g can i n c l u d e r o u t i n e maintenance and minor r e p a i r of the i n s t r u m e n t s . One or two persons can perform most o f these t a s k s , but g e n e r a l l y f o r a f u l l work l o a d , t h r e e o r more persons a r e r e q u i r e d . C l i n i c a l , D i a g n o s t i c , and Research P r o t o c o l s . A summary of the v a r i o u s types o f p r o t o c o l s t h a t have used IVNAA t e c h n i q u e s a r e g i v e n i n T a b l e V. Continued i n t e r e s t i n these a p p l i c a t i o n s i s expected as more r e s e a r c h c e n t e r s e s t a b l i s h t h e i r own f a c i l i t i e s . I n each c a s e , the WHO recommendations (8) s h o u l d be f o l l o w e d i f l o c a l and s t a t e g u i d e l i n e s g o v e r n i n g the use of i o n i z i n g r a d i a t i o n a r e not a v a i l a b l e . A most important a s p e c t of any f a c i l i t y i s to keep the r a d i a t i o n doses at the lowest l e v e l s w i t h o u t l o s s of adequate d i a g n o s t i c or r e s e a r c h v a l u e . Pregnant women and c h i l d r e n under 18 y e a r s of age s h o u l d not be


36


T a b l e V.

C l i n i c a l , D i a g n o s t i c , and Research A p p l i c a t i o n s o f I n V i v o Neutron Activation Analysis


Total Body Calcium and Phosphorus P o p u l a t i o n Group

C l i n i c a l C o n d i t i o n and Research P r o t o c o l s

Normal s u b j e c t s

R e f e r e n c e range f o r age, s e x , race and body size

Aging Osteopenia Osteoporosis

Postmenopausal E f f e c t s , O s t e o g e n e s i s i m p e r f e c t a , Drug induced bone l o s s , V i t a m i n D d e f i c i e n c y s t a t e s , Renal osteodystrophy

Endocrine

C u s h i n g ' s syndrome, Acromegaly, P a r a t h y r o i d d i s o r d e r s , T h y r o i d d i s o r d e r s , Hypogonadism

disorders

Myotonic d y s t r o p h y , T h a l a s s e m i a , A l c o h o l i c c i r r h o s i s , Cadmium-induced bone l o s s

Other D i s o r d e r s

Total Body Nitrogen and Potassium P o p u l a t i o n Group

C l i n i c a l C o n d i t i o n and Research P r o t o c o l s

Normal s u b j e c t s

R e f e r e n c e range f o r age, s e x , race and body size

Athletes/exercise therapy

E f f e c t s o f e x e r c i s e and/or a n a b o l i c agents

Obese s u b j e c t s

V e i g h t r e d u c t i o n programs: c a l o r i c r e s t r i c t i o n , i n t e s t i n a l bypass s u r g e r y , l y p o - s u c t i o n

a

Surgical patients

E v a l u a t i o n of n u t r i t i o n a l management f o l l o w i n g major a b d o m i n a l , c a r d i a c o r t r a n s p l a n t s u r g e r y

3

Protein malnutrition

M a l n u t r i t i o n , E f f e c t s o f d i e t and t o t a l parenteral nutrition

Cancer

Maintance of P r o t e i n Mass - e f f e c t s of cancer therapy and TPN

Renal

Changes o f body c o m p o s i t i o n of p a t i e n t s on d i a l y s i s and w i t h endstage r e n a l f a i l u r e

failure

Cardiovascular

disease

3

Post-MI m o n i t o r i n g of body c o m p o s i t i o n of patients

T h y r o i d and P a r a t h y r o i d

Body c o m p o s i t i o n advance d i s e a s e

changes w i t h treatment and

Patients with ascites

C i r r h o s i s w i t h a s c i t e s and the e f f e c t of an a r t e r i o v e n o u s shunt

Areas where f u t u r e i n v e s t i g a t i o n appear most p r o m i s i n g f o r the study of body c h l o r i n e and sodium i n o b e s i t y w i t h o r w i t h o u t h y p e r t e n s i o n , o r a l c o n t r a c e p t i o n , and u r o l i t h i a s i s .


3. ELLIS


exposed u n l e s s t h e r e a r e c l e a r i n d i c a t i o n s f o r m e d i c a l r e a s o n s . A s i g n e d informed consent s h o u l d be o b t a i n e d f o r each procedure a f t e r p r o t o c o l r e v i e w and a p p r o v a l by the a p p r o p r i a t e i n s t i t u t i o n a l r e v i e w board.


CONCLUSIONS In v i v o measurements o f whole body c a l c i u m and n i t r o g e n , and k i d n e y and l i v e r burdens o f cadmium a r e l i k e l y t o c o n t i n u e i n r e g u l a r use. These measurements can be a p p l i e d t o a v a r i e t y o f c l i n i c a l and t o x i c o l o g i c a l problems; such i n f o r m a t i o n i s v i r t u a l l y u n o b t a i n a b l e by o t h e r means i n the l i v i n g human. The r i s k s i n v o l v e d w i t h each procedure a r e minimal and pose no s i g n i f i c a n t hazard f o r s e q u e n t i a l o b s e r v a t i o n s i n the same s u b j e c t s and f o r i n d i v i d u a l s i n the g e n e r a l p o p u l a t i o n . The r a d i a t i o n dosages a r e g e n e r a l l y low compared w i t h many common r a d i o l o g i c a l e x a m i n a t i o n s and d i a g n o s t i c t e s t s ( 3 ^ ) . When a new a c t i v a t i o n f a c i l i t y i s planned, one s h o u l d expect t o s t a r t w i t h measurements o f a t l e a s t one o f these t h r e ^ e l e m e n t s ^ A l though the p r e f e r r e d n e u t r o n s o u r c e i s p r o b a b l y Am/Be, Cf may be more a c c e s s i b l e . Pu s o u r c e s s h o u l d not be c o n s i d e r e d u n l e s s a l r e a d y a v a i l a b l e t o the u s e r ; these s o u r c e s r e q u i r e e x t e n s i v e r e g u l a t o r y c o n t r o l and s e c u r i t y . The p r e f e r r e d method o f measuring n i t r o g e n i s undoubtedly t o use i t s neutron c a p t u r e gammas, whereas a m u l t i - e l e m e n t a l a n a l y s i s o f body sodium, c h l o r i n e , phosphorus, and c a l c i u m i s best c a r r i e d out a t p r e s e n t u s i n g the d e l a y e d s p e c t r a . Areas of f u r t h e r development a r e l i k e l y t o focus on body carbon and oxygen as measures o f body f a t and water, r e s p e c t i v e l y . At p r e s e n t , N a l d e t e c t o r s s h o u l d be used, because o f the p r o h i b i t i v e c o s t a s s o c i a t e d w i t h the number o f Ge d e t e c t o r s t h a t would be needed f o r these measurements. The N a l c r y s t a l s s h o u l d be r e l a t i v e l y l a r g e (>2000 cc volume) to have r e a s o n a b l e e f f i c i e n c y f o r d e t e c t i n g h i g h energy gammas (1-11 Mev). C o m m e r c i a l l y a v a i l a b l e e l e c t r o n i c s f o r gamma s p e c t r o s c o p y and computer-based d a t a c o l l e c t i o n systems a r e more than adequate f o r the t a s k s a s s o c i a t e d w i t h IVNAA. The commercial a n a l y t i c a l s o f t w a r e programs a r e g e n e r a l l y adequate, a l t h o u g h some a d d i t i o n a l m o d i f i c a t i o n s a r e u s u a l l y needed to conform t o the g e o m e t r i c a l d e s i g n o f the system, number o f d e t e c t o r s , and the specific i n vivo application. When p l a n n i n g IVNAA s t u d i e s o f body c o m p o s i t i o n , i t i s i m p o r t a n t t o c o n s i d e r o t h e r ' n o n i n v a s i v e ' t e c h n i q u e s which may a l s o be a v a i l a b l e . F o r example, t h e r e a r e a l t e r n a t i v e means by which t o measure bone m i n e r a l , such as r a d i o g r a p h y , photon a b s o r p t i o m e t r y , Compton s c a t t e r i n g , and CT s c a n n i n g . None o f these methods i n c l u d i n g IVNAA i s l i k e l y t o d i s p l a c e a l l o t h e r s . T o t a l body c a l c i u m measurements, however, c o n t i n u e t o p r o v i d e unique and v a l u a b l e d a t a t h a t have been the ' r e f e r e n c e s t a n d a r d ' f o r comparison w i t h these a l t e r n a t e t e c h n i q u e s . N u c l e a r magnetic resonance s p e c t r o s c o p y o f body n i t r o g e n , sodium, and phosphorus remains a c o n s i d e r a t i o n ; i t s development, however, w i l l c o n t i n u e t o be d e l a y e d u n t i l p r o t o n mapping t e c h n i q u e s f o r imaging a r e f u l l y developed.


38



ACKNOWLEDGMENTS The a u t h o r thanks E.R. K l e i n , J.D. Eastman, and S. Smith f o r e d i t o r i a l a s s i s t a n c e and p r e p a r a t i o n o f the m a n u s c r i p t . T h i s work i s a p u b l i c a t i o n o f the USDA/ARS C h i l d r e n ' s N u t r i t i o n R e s e a r c h C e n t e r , Department o f P e d i a t r i c s , B a y l o r C o l l e g e o f M e d i c i n e and Texas C h i l d r e n ' s H o s p i t a l , Houston, TX. T h i s p r o j e c t has been funded w i t h f e d e r a l funds from the USDA/ARS under C o o p e r a t i v e Agreement No. 58-7MN1-6-100. The c o n t e n t s o f t h i s p u b l i c a t i o n do not n e c e s s a r i l y r e f l e c t the views o r p o l i c e s o f the USDA, nor does mention o f the t r a d e names, commercial p r o d u c t s , o r o r g a n i z a t i o n s imply endorsement by the US Government.

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Planning In Vivo Body Composition Studies in Humans - ACS

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