CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (42,119,000)	$ (34,151,000)	$ (14,494,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	2,769,000	2,837,000	1,421,000
Depreciation and amortization	908,000	652,000	447,000
Amortization of discount on notes payable and debt issuance costs	33,000	235,000	430,000
Amortization of expenses paid in shares of common stock		956,000	239,000
Common stock issued for services		40,000
Loss on sale of property	2,000		49,000
Changes in operating assets and liabilities:
Trade and other receivables, net	(964,000)	92,000	289,000
Government contract receivables	93,000	274,000	1,577,000
Inventories, net	1,673,000	(2,161,000)	1,584,000
Prepaid expenses and other current assets, net	158,000	95,000	(777,000)
Other non-current assets	789,000	(7,000)	183,000
Accounts payable	(601,000)	608,000	(484,000)
Accrued clinical trial site and related fees	(181,000)	984,000	602,000
Accrued payroll and related expenses	1,013,000	(168,000)	43,000
Deferred revenue	(2,237,000)	3,843,000	(1,370,000)
Deferred government contract revenue		(78,000)	(3,793,000)
Customer deposits	3,106,000	(859,000)	331,000
Other accrued expenses and current liabilities	(62,000)	372,000	(232,000)
Other long-term liabilities	(258,000)	(26,000)	(6,000)
Net cash used in operating activities	(35,878,000)	(26,462,000)	(13,961,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions	(1,554,000)	(912,000)	(208,000)
Proceeds from sale of property			20,000
Decrease (increase) in other assets	383,000	(435,000)	(80,000)
Net cash used in investing activities	(1,171,000)	(1,347,000)	(268,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs of $1,151,000, $769,000, and $850,000, respectively	33,179,000	33,087,000	25,474,000
Proceeds from exercise of stock options		44,000	105,000
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	236,000	134,000
Principal payments on notes payable	(1,333,000)	(2,000,000)	(1,667,000)
Principal payments on capital leases	(75,000)	(62,000)	(20,000)
Net cash provided by financing activities	32,007,000	31,203,000	23,892,000
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(5,042,000)	3,394,000	9,663,000
CASH AND CASH EQUIVALENTS, Beginning of year	23,075,000	19,681,000	10,018,000
CASH AND CASH EQUIVALENTS, End of year	18,033,000	23,075,000	19,681,000
SUPPLEMENTAL INFORMATION:
Interest paid	68,000	301,000	535,000
SCHEDULE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Property acquired under capital lease		180,000	78,000
Accounts payable and other liabilities for purchase of property	47,000	300,000	18,000
Other asset in exchange for future services		$ 233,000